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\DOI{10.5802/crchim.459}
\datereceived{2026-02-06}
\daterevised{2026-05-06}
\dateaccepted{2026-06-12}
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\section*{Declaration of interests}
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\COI{The authors do not work for, advise, own shares in, or receive
funds from any organization that could benefit from this article, and
have declared no affiliations other than their research organizations.}

\begin{document}

\begin{noXML}

\CDRsetmeta{articletype}{review}

\editornote{Article submitted by invitation}
\alteditornote{Article soumis sur invitation}

\title{Fluorescent dendrimers and related branched polymers: synthetic
strategies for peripheral modification with organic fluorophores}

\alttitle{Dendrim\`{e}res fluorescents et polym\`{e}res ramifi\'{e}s
apparent\'{e}s : strat\'{e}gies de synth\`{e}se pour la modification
p\'{e}riph\'{e}rique \`{a} l'aide de fluorophores organiques}

\author{\firstname{Desislava} \lastname{Staneva}\CDRorcid{0000-0001-7556-1222}\IsCorresp}
\address{Department of Textile, Leather and Fuels, 
University of Chemical Technology and Metallurgy, 
1756, Sofia, Bulgaria}
\email[D. Staneva]{grabcheva@mail.bg}

\author{\firstname{Paula} \lastname{Bosch}}
\address{Institute of Science and Technology of Polymers, 
Spanish National Research Council (ICTP-CSIC), 
28006 Madrid, Spain}

\author{\firstname{Ivo} \lastname{Grabchev}\CDRorcid{0000-0001-7204-8183}\IsCorresp}
\address{Faculty of Medicine, Sofia University ``St. Kliment Ohridski'', 
1407, Sofia, Bulgaria}
\email[I. Grabchev]{ohig@chem.uni-sofia.bg}

\keywords{\kwd{Fluorescent dendrimers} 
\kwd{Branched polymers} 
\kwd{Organic fluorophores} 
\kwd{1,8-naphthalimides}}

\altkeywords{\kwd{Dendrim\`{e}res fluorescents}
\kwd{Polym\`{e}res ramifi\'{e}s}
\kwd{Fluorophores organiques}
\kwd{1,8-naphtalimides}}

\thanks{European Union Next Generation EU through National Recovery
and Resilience Plan of the Republic of Bulgaria (Project Nos.
BG-RRP-2.004-0008 and BG-RRP-2.004-0002), ``BiOrgaMCT'', European
Union NextGeneration EU through CSIC Interdisciplinary Thematic
Platform Salud Global$+$ (PTI-SALUDGLOBAL$+$)} 

\begin{abstract}
This review is devoted to our systematic investigations into the
synthesis of fluorescent dendrimers within the broader context of
developing functional dendrimer architectures. The main emphasis is
placed on synthetic methods for the peripheral modification of
poly(amidoamine) (PAMAM) and poly(propylene imine) (PPI) dendrimers
with organic fluorophores, enabling the creation of well-defined
photoactive macromolecules with controlled structure and properties. In
the presented studies, a series of fluorescent dendrimers and
hyperbranched polymers functionalized with various chromophoric
systems, such as 1,8-naphthalimide, benzanthrone, acridine, and
nitrobenzofurazan, has been reported. The applied synthetic approaches
provide precise control over the degree of functionalization and the
distribution of photoactive groups at the dendrimer periphery. The main
objective of this review is to highlight the synthetic methodologies
and structure--property relationships that determine the potential of
fluorescent dendrimers as platforms for developing new functional
materials with biological and sensing properties. First examples of
fluorescent hyperbranched polymers are also included, allowing a direct
comparison between strictly defined dendrimer architectures and
statistically branched macromolecular systems. Water-soluble
fluorescent dendrimers are briefly discussed as an extension of the
synthetic strategies applied. Application-oriented aspects of
fluorescent dendrimers are outlined.
\end{abstract}

\begin{altabstract}
Cette revue est consacr\'{e}e \`{a} nos recherches syst\'{e}matiques
sur la synth\`{e}se de dendrim\`{e}res fluorescents dans le cadre plus
large du d\'{e}veloppement d'architectures fonctionnelles de
dendrim\`{e}res. L'accent est principalement mis sur les m\'{e}thodes
de synth\`{e}se permettant la modification p\'{e}riph\'{e}rique de
dendrim\`{e}res de type poly(amidoamine) (PAMAM) et poly(propyl\`{e}ne
imine) (PPI) avec des fluorophores organiques, ce qui permet de
cr\'{e}er des macromol\'{e}cules photoactives bien d\'{e}finies, dont
la structure et les propri\'{e}t\'{e}s sont contr\^{o}l\'{e}es. Dans
les \'{e}tudes pr\'{e}sent\'{e}es, une s\'{e}rie de dendrim\`{e}res
fluorescents et de polym\`{e}res hyperramifi\'{e}s fonctionnalis\'{e}s
avec divers syst\`{e}mes chromophores, tels que le 1,8-naphtalimide, la
benzanthrone, l'acridine et le nitrobenzofurazane, est rapport\'{e}e.
Les approches synth\'{e}tiques appliqu\'{e}es permettent un
contr\^{o}le pr\'{e}cis du degr\'{e} de fonctionnalisation et de la
distribution des groupes photoactifs \`{a} la p\'{e}riph\'{e}rie des
dendrim\`{e}res. L'objectif principal de cette revue est de mettre en
\'{e}vidence les m\'{e}thodologies de synth\`{e}se et les relations
structure-propri\'{e}t\'{e} qui d\'{e}terminent le potentiel des
dendrim\`{e}res fluorescents en tant que plateformes pour le
d\'{e}veloppement de nouveaux mat\'{e}riaux fonctionnels dot\'{e}s de
propri\'{e}t\'{e}s biologiques et de d\'{e}tection. Les premiers
exemples de polym\`{e}res hyperramifi\'{e}s fluorescents sont
\'{e}galement inclus, permettant une comparaison directe entre des
architectures de dendrim\`{e}res strictement d\'{e}finies et des
syst\`{e}mes macromol\'{e}culaires \`{a} ramification statistique. Les
dendrim\`{e}res fluorescents hydrosolubles sont bri\`{e}vement
abord\'{e}s dans le prolongement des strat\'{e}gies de synth\`{e}se
appliqu\'{e}es. Les aspects orient\'{e}s vers les applications des
dendrim\`{e}res fluorescents sont pr\'{e}sent\'{e}s.
\end{altabstract}

%\input{CR-pagedemetas}

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\section{Introduction}\label{sec1}
Dendrimers represent a unique class of 
synthetic polymers with
precisely defined structures, 
{characterized} by high branching,
monodispersity, and well-controlled surface functionalization. Owing to
these structural features, dendrimers occupy an important position
among modern functional polymers and find applications across a wide
range of~contemporary, highly relevant scientific 
{fields~\cite{1,2,3,4,5}.}\looseness=-1

An important characteristic of dendrimers is the ability to modify
their periphery, allowing the introduction of various functional groups
without compromising the integrity of the dendrimer structure. This
approach is particularly advantageous for the development of
fluorescent dendrimers, where the peripheral attachment of photoactive
chromophores combines the benefits of the dendrimer matrix with the
optical properties of low-molecular-weight fluorophores, with
applications in sensing, catalysis, optics, and materials 
science~\cite{6,7,8,9,10}. Fluorescent dendrimers are of interest both
from a fundamental perspective, for investigating structure--property
relationships, and for their potential to develop new functional
materials. Compared to low-molecular-weight fluorophores,
dendrimer-based systems often exhibit enhanced stability, multivalency,
and improved control over the spatial distribution of photoactive
centers. These features make them promising platforms for the rational
design of photoactive macromolecular  systems~\cite{11,12,13}. In
addition, fluorescent dendrimers are employed as contrast agents in
fluorescence microscopy and other bioimaging techniques, facilitating
the diagnosis of various  
\mbox{diseases~\cite{14,15}.}


Fluorescent dendrimers can be designed to act as carriers of
therapeutic agents while enabling monitoring of their 
distribution~\cite{16,17,18,19}. Furthermore, by conjugating specific
fluorophores and recognition units to dendrimers, fluorescent sensors
can be designed to monitor changes in environmental and biological
systems, including pH, ionic strength, 
temperature, the presence of
metal ions, biomolecules, or toxins. In these cases, the role of
dendrimers is to provide a stable platform and a unique
\mbox{microenvironment} that enhances sensor 
performance~\cite{20,21,22,23,24,25}.

Fluorophores can be incorporated into dendrimer structures through
covalent attachment to 
\mbox{peripheral} functional groups or by
encapsulation, where the fluorophores are located within internal
cavities or the dendrimer core. Alternatively, fluorophores may be
integrated as structural elements within the dendrimer core or
branching  units~\cite{26,27}. Peripheral covalent attachment ensures
high stability of the resulting systems and prevents undesired
aggregation or migration of the fluorophores. In such systems,
dendrimers contain a large number of closely spaced chromophores that
may act 
\mbox{independently} or 
\mbox{interact} with each other. This phenomenon is
commonly referred to as the ``dendrimer effect'', which has been
extensively discussed in the  
\mbox{literature~\cite{28,29}.}

Among the wide variety of organic fluorophores, 1,8-naphthalimides (NI)
have emerged as a particularly useful class of fluorophores, owing to
their high fluorescence quantum yields, excellent photostability, and
the possibility for facile functionalization at the C-4 position and
the imide nitrogen atom, which facilitates their covalent attachment to
dendrimers~\cite{30,31}. The polarization of the 1,8-naphthalimide
molecule arises from donor--acceptor interactions between the
electron-accepting carbonyl groups of the imide moiety and substituents
at the C-4 position of the naphthalene  ring~\cite{32}. Amino
substituents (--NH\tsub{2}, --NHR, --NR\tsub{2}) and alkoxy substituents
(--OR) act as effective electron donors, giving rise to internal charge
transfer (ICT) processes. Because nitrogen is less electronegative than
oxygen, its lone electron pair is more efficiently delocalized toward
the 1,8-naphthalimide acceptor compared to alkoxy substituents. In
solution, 4-alkoxy-substituted 1,8-naphthalimides typically absorb in
the ultraviolet spectral region and emit violet--blue fluorescence,
whereas amino-substituted 1,8-naphthalimides absorb in the visible
region and emit yellow--green fluorescence. Thus, by varying the
electron-donating ability of substituents at the C-4 position, the
synthesis of 1,8-naphthalimide derivatives with predefined and tunable
emission colors and fluorescence intensities can be rationally 
designed~\cite{32}.
\looseness=1

In recent years, the biological activity of 1,8-naphthalimide
derivatives has been intensively investigated for applications in
biomedicine and  biology~\cite{33,34,35,36,37}. The planar core of the
1,8-naphthalimide molecule enables intercalation between DNA base
pairs, disrupting the normal double-helical structure. This process
inhibits DNA replication and transcription during cancer cell
proliferation, ultimately inducing cell death, including through
autophagy. In addition, 1,8-naphthalimides and their metal complexes
exhibit significant potential as antibacterial and antifungal 
agents~\cite{38,39,40}. Certain 1,8-naphthalimide derivatives have also
been employed as photosensitizers in antibacterial photodynamic 
therapy~\cite{41,42,43}. Upon light irradiation, they generate reactive
oxygen species (ROS), which are highly cytotoxic toward both
Gram-positive and Gram-negative bacteria.

Owing to their favorable photophysical and biological properties,
1,8-naphthalimides represent a highly attractive chromophoric system
for the modification of dendrimers bearing peripheral primary amino
groups. Their synthesis is based on covalent attachment via
condensation of 1,8-naphthalimide anhydrides with primary amines, which
constitutes a typical example of ``peripheral modification''. This
approach provides a high degree of control over the number and nature
of the functional groups introduced, forming the basis for the
multifunctionality of the resulting  dendrimers~\cite{44,45,46}.

Studies on fluorescent dendrimer systems modified with
1,8-naphthalimide fluorophores have focused on biomedical applications,
cell and tissue  imaging~\cite{47}, detection of metal ions and
protons~\cite{24}, and investigation of dendrimer interactions with
bacterial cell  membranes~\cite{48,49}, among others. By enabling
control over the number and spatial distribution of fluorophores within
the dendrimer structure, these hybrid nanomaterials allow fine tuning
of optical properties and selectivity toward specific molecules or
environmental 
\mbox{conditions.}

This review presents a comprehensive overview of our investigations
into the synthesis of fluorescent dendrimers with different
architectures and peripheral modifications. Particular emphasis is
placed on the synthetic strategies and methodologies employed for the
modification of poly(amidoamine) and poly(propylene imine) dendrimers
with various organic fluorophores, as well as on the first syntheses of
hyperbranched polymers with related photoactive functionalities.
Biological and sensing applications are addressed only briefly to
emphasize their direct relationship with the synthetic design of the
dendrimer systems presented.

\section{Design principles of fluorescent PAMAM and PPI 
dendrimers}\label{sec2}
The design of fluorescent dendrimers is based on combining a
well-defined dendrimer architecture with deliberately introduced
photoactive groups. A major advantage of dendrimer systems is the
possibility of controlling the number, distribution, and chemical
nature of functional groups at the macromolecular periphery,
particularly in systems with a high or complete degree of
functionalization. This enables systematic investigation of
structure--photophysical property relationships and opens pathways
toward the development of fluorescent materials with predefined
characteristics.

In the development of fluorescent dendrimers, the choice of dendrimer
matrix is crucial. Poly(amidoamine) (PAMAM) and poly(propylene imine)
(PPI) dendrimers are distinguished by their well-defined structures,
reactive terminal amino groups, and high synthetic reproducibility.
These features make them suitable platforms for peripheral
functionalization with organic fluorophores without significantly
perturbing the dendrimer core 
\mbox{structure.}

\subsection{Synthesis of PAMAM dendrimers modified with
1,8-naphthalimides}\label{sec2.1}
For the first time, PAMAM dendrimers of  zero~\cite{44} and
second~\cite{45} generations, peripherally modified with
1,8-naphthalimide chromophores, were synthesized, enabling precise
control over the degree of functionalization and the distribution of
fluorophores on the macromolecular surface. The objective of this
modification was to investigate their ability to detect metal ions and
protons via a photoinduced electron transfer (PET) 
mechanism~\cite{50}. These initial studies demonstrated the potential
of dendrimers as highly sensitive optical fluorescent sensors for the
detection of metal ions and protons, using dendrimer-bound
1,8-naphthalimide units as signal transducers.

Subsequent investigations further developed this concept by
synthesizing a series of new PAMAM and PPI dendrimers functionalized
with 1,8-naphthalimide units, which exhibit sensing 
properties~\cite{24}. The selection of 1,8-naphthalimides as
fluorophores for dendrimer modification was based on extensive prior
experience with monomeric low-molecular-weight fluorophores and their
covalent attachment to linear  polymers~\cite{51,52,53,54,55,56}. In
contrast, these fluorophores had not been previously used to modify
dendrimers. Owing to the dendrimer effect, peripheral 1,8-naphthalimide
units can induce signal amplification, as the overall fluorescence
response represents a cumulative contribution of multiple chromophoric
units. In several dendrimer 
\mbox{systems,} it has been demonstrated that the
individual photophysical properties of the chromophores are largely
preserved, without significant fluorescence self-quenching. This
behavior is attributed to the spatial separation of the chromophoric
units within the dendritic framework, which limits $\uppi$--$\uppi$
stacking  interactions~\cite{24,44,45,57}.

To investigate structure--function relationships, substituents of
different electronic nature were introduced at the C-4 position of the
1,8-naphthalimide units in low-generation dendrimers. Nitro groups and
bromine atoms exhibit pronounced electron-accepting properties, which
prevent effective polarization of the chromophoric system and
fluorescence emission. Consequently, these substituents have to be
replaced by electron-donating amino or alkoxy groups possessing a
mesomeric (${+}$M) effect. Nitro- and halogen-substituted
1,8-naphthalimides are classical activated systems for nucleophilic
aromatic substitution, allowing efficient introduction of amino and
alkoxy groups at the C-4 position, and are widely employed in the
synthesis of functional fluorescent  derivatives~\cite{58,59}.

Scheme~\ref{sch1} illustrates the condensation reaction between
4-nitro-1,8-naphthalic anhydride and the terminal amino groups of a
first-generation PAMAM dendrimer, followed by nucleophilic substitution
of the nitro group by amino substituents of different nature. In this
manner, various 4-amino-substituted 1,8-naphthalimide derivatives were
obtained, covalently attached to the dendrimer periphery 
(Scheme~\ref{sch2}).

\begin{scheme}
\vspace*{6pt}
\includegraphics{sc01}
\vspace*{12pt}
\caption{\label{sch1}Modification of first-generation PAMAM dendrimer
with 1,8-naphthalimides.}
\end{scheme}

\begin{scheme*}
\vspace*{-2pt}
\includegraphics{sc02}
\vspace*{4pt}
\caption{\label{sch2}Peripherally modified first-generation PAMAM
dendrimers bearing 1,8-naphthalimide units.}
\end{scheme*}

The first-generation PAMAM dendrimer modified with eight
4-nitro-1,8-naphthalimide units \textbf{1} was further used as a
starting material for the synthesis of \textbf{6} a blue-emitting
fluorescent dendrimer bearing an $N$,$N$-dimethylaminoethoxy
substituent (--OCH\tsub{2}CH\tsub{2}N(CH\tsub{3})\tsub{2}) at the C-4 position
of the 1,8-naphthalimide core. Its design follows the
fluorophore--spacer--receptor concept, in which the
$N$,$N$-dimethylamino group (--N(CH\tsub{3})\tsub{2}), containing a
tertiary nitrogen atom with a nonbonding electron pair, acts as the
receptor moiety for metal ions and protons and is linked to the
1,8-naphthalimide signaling unit via an ethylene spacer
(--CH\tsub{2}CH\tsub{2}--)~\cite{60}. 

\nocite{61}

The nucleophilic substitution of the nitro group by the 
$N$,$N$-dimethylaminoethoxy substituent was carried out in DMF in the
presence of alkaline agents. In addition, a dendrimer bearing a 
\mbox{primary}
amino group as a substituent at the C-4 
position of the
1,8-naphthalimide structure was obtained in a single-step synthesis via
the reaction of 4-amino-1,8-naphthalic anhydride with the PAMAM 
\mbox{dendrimer~\cite{62}.}

Using the same synthetic strategy, PAMAM dendrimers of zero and second
generation were analogously prepared, peripherally modified with four
and sixteen 1,8-naphthalimide units, respectively, bearing different
substituents at the C-4 position of the naphthalene core
(Scheme~\ref{sch3}).

\begin{scheme*}
\includegraphics{sc03}
\vspace*{4pt}
\caption{\label{sch3}PAMAM dendrimers modified with 1,8-naphthalimides
from zero and second generations.}
\vspace*{-10pt}
\end{scheme*}

\subsection{Peripheral modification of PPI\newline 
dendrimers of different
generations with\newline 
1,8-naphthalimide derivatives}\label{sec2.2}
Poly(propylene imine) dendrimers are an alternative dendrimer
architecture, characterized by a more hydrophobic internal structure
compared to PAMAM dendrimers. As with PAMAM systems, terminal primary
amino groups are used for peripheral modification with fluorophores.
Within our studies, fluorescent PPI dendrimers peripherally modified
with organic fluorophores were synthesized for the first time, using
synthetic methodologies analogous to those applied for PAMAM dendrimers
but adapted to the specific chemistry of the PPI matrix. This approach
enables a direct comparison between the two dendrimer types and allows
assessment of the 
influence of dendrimer architecture on the
photophysical properties of the resulting macromolecules.

Peripheral modification of PPI dendrimers was achieved through covalent
attachment of fluorophoric units to the terminal amino groups. Various
fluorophores were employed, including derivatives of 1,8-naphthalimide,
benzanthrone, acridine, and nitrobenzofurazan, thereby extending the
spectral range and enabling systematic investigation of the influence
of chemical structure on photophysical characteristics.

\subsubsection{Synthesis of first-generation PPI\newline 
dendrimers bearing
4-amino-substituted\newline 
1,8-naphthalimide units}\label{sec2.2.1} 
In the design of fluorescent PPI dendrimers, synthetic schemes and
substituents at the C-4 position analogous to those used for PAMAM
dendrimers were employed  (Scheme~\ref{sch4}).

\begin{scheme*}
\includegraphics{sc04}
\vspace*{4pt}
\caption{\label{sch4}First-generation PPI dendrimers peripherally
modified with 1,8-naphthalimide derivatives.}
\vspace*{-10pt}
\end{scheme*}

\begin{scheme*}
\vspace*{2pt}
\includegraphics{sc05}
\vspace*{4pt}
\caption{\label{sch5}Ultrasonic synthesis of a first-generation PPI
dendrimer bearing
4-$N$,$N$-dimethylaminoethoxy-1,8-naphthalimide units
at the periphery.}
\vspace*{2pt}
\end{scheme*}

\begin{scheme*}
\includegraphics{sc06}
\vspace*{4pt}
\caption{\label{sch6}Second-generation PPI dendrimers peripherally
modified with 1,8-naphthalimide derivatives.}
\vspace*{-10pt}
\end{scheme*}

\nocite{63,64,65,66,67,68,69,70,71,74}

\subsubsection{Synthesis of PPI  dendrimer 31 bearing\newline
4-alkoxy-1,8-naphthalimide units}\label{sec2.2.2} 
Ultrasonic irradiation is a well-established sonochemical method for
synthesis, enabling reduced reaction time and increased yields in
nucleophilic substitution reactions of the nitro group in
4-nitro-1,8-naphthalimides with alkoxy substituents (alcoholate anions,
--OR)~\cite{72,73}. The reaction proceeds via a nucleophilic aromatic
substitution (S\tsub{N}Ar) mechanism, while ultrasonic
irradiation provides the energy and mechanical effects that accelerate
both the generation of reactive species and the substitution.

In contrast to conventional thermal heating, where the entire reaction
volume is maintained at elevated temperature, sonochemical conditions
allow the bulk solution to remain close to room  temperature~\cite{72}.
This significantly reduces or eliminates side reactions and product
degradation that may occur during prolonged high-temperature heating,
thereby increasing the purity and yields of 4-alkoxy-1,8-naphthalimide
derivatives. A blue-emitting fluorescent PPI dendrimer was obtained
through nucleophilic substitution of the nitro group by an
--OCH\tsub{2}CH\tsub{2}N(CH\tsub{3})\tsub{2} residue using ultrasonic
synthesis. The reaction was carried out in 
$N$,$N$-dimethylaminoethanol, which served 
\mbox{simultaneously} as both
reagent and reaction medium. Under these conditions, a blue-fluorescent
PPI dendrimer  \textbf{31} was obtained in nearly 
quantitative yield
and high purity, as shown in\unskip\break 
Scheme~\ref{sch5}~\cite{74}.

\subsubsection{Synthesis of second- and third-generation PPI dendrimers
bearing 4-amino-substituted\newline 
1,8-naphthalimide units}\label{sec2.2.3} 
Fluorescent PPI dendrimers bearing eight 4-amino-substituted
1,8-naphthalimide units were obtained via condensation of a
second-generation PPI dendrimer with 4-nitro-1,8-naphthalic anhydride,
followed by nucleophilic substitution of the nitro group by various
amines in DMF. In addition, 4-bromo-1,8-naphthalic anhydride and
1,8-naphthalic anhydride were also employed as starting materials 
(Scheme~\ref{sch6}).

\begin{scheme*}
\vspace*{2pt}
\includegraphics{sc07}
\vspace*{7pt}
\caption{\label{sch7}Third-generation PPI dendrimer \textbf{40}
peripherally modified with 4-amino-1,8-naphthalimide units.}
%\vspace*{-10pt}
\end{scheme*}

A PPI dendrimer bearing sixteen terminal primary amino groups was
reacted with 4-amino-1,8-naphthalic anhydride, yielding dendrimer 
\textbf{40} with the structure shown in  Scheme~\ref{sch7} (yield 
82\%)~\cite{71}. In contrast, peripheral modification of the same
dendrimer with 4-nitro-1,8-naphthalimide was 
\mbox{complicated} by the poor
solubility of the reaction system and the reduced reactivity associated
with this nitro-substituted precursor, leading to incomplete
functionalization and products with different degrees of substitution.
Because of the limited synthetic control achieved, this approach was
not further pursued.

The dendrimers described were isolated in the solid state and exhibit
good stability upon prolonged storage under ambient conditions. They
are readily soluble in common organic solvents but are insoluble in
water.

\subsection{PPI dendrimers modified with other\newline
fluorophores}\label{sec2.3}
In addition to 1,8-naphthalimides, fluorescent PPI dendrimers modified
with other classes of organic fluorophores---namely
benzanthrone, acridine, and nitrobenzofurazan---were
developed within our studies. The aim of this approach was to extend
the spectral range of fluorescent dendrimer systems and to demonstrate
the versatility of the synthetic methodologies applied across different
chromophoric structures.

\nocite{75,76,77,78}

\subsubsection{Synthesis of a second-generation PPI dendrimer modified
with benzanthrone \textbf{(41)}}\label{sec2.3.1}
Benzanthrone is a polycyclic aromatic ketone with an extended
$\uppi$-conjugated system, which accounts for its strong absorption and
intense fluorescence in the long-wavelength region of the visible
spectrum. A characteristic feature of benzanthrone derivatives is their
high photostability and relatively large Stokes shift, making them
suitable for applications requiring stable fluorescence signals with
minimal self-absorption. Interest in benzanthrone-based fluorophores
also arises from pronounced intramolecular charge-transfer character,
which renders their fluorescence sensitive to medium polarity and
structural  modifications~\cite{79,80,81}.

A fluorescent dendrimer modified with benzanthrone chromophores was
obtained via peripheral functionalization of a second-generation PPI
dendrimer using a  benzanthrone derivative bearing a reactive
chloromethyl group 
(2-chloro-$N$-(7-oxo-7H-benzo[de]anthracen-3-yl)acetamide) with a yield
of 82\%. The benzanthrone precursor had been previously reported and 
characterized~\cite{80}.

\begin{scheme*} 
\includegraphics{sc08}
\vspace*{6pt}
\caption{\label{sch8}Chemical structure of a second-generation PPI
dendrimer modified with benzanthrone units.}
\vspace*{-4pt}
\end{scheme*}

The modification proceeds through nucleophilic substitution of the
chlorine atom in the 
\mbox{chloroacetamide} fragment by the primary amino
groups of the dendrimer, resulting in the formation of stable amide
bonds and covalent attachment of benzanthrone units to the dendrimer
periphery  (Scheme~\ref{sch8})~\cite{82}. The structure of the
dendrimer obtained, bearing eight benzanthrone units, is supported by
MALDI-TOF mass spectrometry, elemental analysis, and NMR spectroscopy.
In particular, the \tsup{1}H NMR spectrum exhibits characteristic
NHCO signals in the region 10.92--10.56~ppm corresponding to eight
amide protons, confirming the formation of amide linkages and excluding
the formation of tertiary amine structures. The absence of
polysubstitution on a single nitrogen atom is attributed to steric
hindrance within the dendritic structure, which limits further
substitution. According to the data reported in  ref.~\cite{82}, the
incorporation of benzanthrone units into the dendrimer structure
results in fluorescent macromolecular systems in which the
photophysical properties of the chromophores are largely preserved,
without significant fluorescence quenching. These results demonstrate
the feasibility of introducing bulky fluorophores into dendrimer
architectures via peripheral modification.

\subsubsection{Synthesis of a second-generation PPI dendrimer modified
with acridine \textbf{(42)}}\label{sec2.3.2}
Acridine and its derivatives represent a class of heteroaromatic
compounds with well-defined fluorescent properties arising from their
planar 
\mbox{$\uppi$-conjugated} structure. They are characterized by
relatively high fluorescence quantum yields and good photostability,
which makes them suitable for a variety of photonic and sensing
applications. Of particular interest is the ability of acridine
fluorophores to participate in proton-dependent and electron-transfer 
processes~\cite{83,84}. Protonation of the nitrogen atom in the
acridine scaffold leads to significant changes in absorption and
emission properties, rendering these compounds sensitive to pH
variations and attractive for sensing applications. 

In our studies, peripheral modification of a PPI dendrimer via covalent
attachment of acridine fragments has been  reported~\cite{85}. Acridine
fluorophores are of interest due to their favorable photophysical
characteristics and biological activity. The synthesis was carried out
by reacting 9-chloroacridine with a PPI dendrimer in a phenolic medium
at elevated temperature under an inert atmosphere. Due to the formation
of a protonated dendrimer species in the reaction medium, the isolated
solid product was converted to its neutral form by dissolution 
in a \mbox{water/ammonia} solution (approximately  pH~8)~\cite{85}.
\looseness=-1

This acridine-modified dendrimer complements the previously developed
naphthalimide- and benzanthrone-based dendrimers and further 
expands
the possibilities for the rational design of fluorescent materials with
diverse spectral 
properties.

\begin{scheme*}
\vspace*{3pt}
\includegraphics{sc09}
\vspace*{5pt}
\caption{\label{sch9}Chemical structure of a second-generation PPI
dendrimer modified with acridine \textbf{(42)} and 4-nitrobenzofurazan
\textbf{(43)}.}
%\vspace*{-10pt}
\end{scheme*}

\subsubsection{Synthesis of a second-generation PPI dendrimer modified
with 4-nitrobenzofurazan \textbf{(43)}}\label{sec2.3.3}
4-Nitrobenzofurazan is a strongly electron-deficient heteroaromatic
fluorophore distinguished by pronounced donor--acceptor
characteristics. The presence of a nitro group combined with the
benzofurazan ring leads to intense charge-transfer transitions,
resulting in high sensitivity of spectral properties to the surrounding
environment and chemical interactions. As a fluorophore,
4-nitrobenzofurazan is particularly attractive due to its ability to
respond to nucleophilic attack and changes in electron density, which
makes it suitable for sensing applications. Despite their lower
fluorescence intensity compared to other fluorophores, benzofurazan
derivatives are valuable for their high sensitivity and the possibility
of fine-tuning their properties through molecular  design~\cite{86,87}.

A new fluorescent dendrimer with a high yield of 97\% was obtained by
peripheral modification of a second-generation PPI dendrimer with
4-nitrobenzofurazan  fragments~\cite{88}. The synthesis is based on
direct nucleophilic aromatic substitution, in which the primary amino
groups of the PPI dendrimer react with 4-chloro-7-nitrobenzofurazan,
employed as a highly electrophilic chromophoric precursor 
(Scheme~\ref{sch9}). Bonding of 4-nitrobenzofurazan units into the
dendrimer structure imparts new photochemical properties, as the
chromophore becomes fluorescent upon substitution of the chlorine atom
by the electron-donating alkylamino groups of the dendrimer.

These syntheses represent the first examples of peripheral modification
of PPI dendrimers with benzanthrone, acridine, and 4-nitrobenzofurazan
chromophores, achieved by applying established synthetic methodologies
for peripheral functionalization. This approach enables the transfer of
synthetic strategies from one class of fluorophores to another, thereby
expanding the possibilities for developing fluorescent dendrimers with
tunable spectral 
\mbox{characteristics.}

\section{Water-soluble and charged fluorescent\newline 
dendrimers}\label{sec3}
Water-soluble fluorescent dendrimers represent a logical extension of
studies on hydrophobic systems and demonstrate the adaptability of
dendrimer architectures to specific environmental conditions. Their
development constitutes an important step toward expanding the
application potential of fluorescent dendrimers in biomedicine and
sensing, while simultaneously imposing specific demands on synthetic
design. Although biological and sensing applications are addressed only
briefly in the present review, the synthetic approaches and
architectural solutions described in this  section provide a foundation
for the further development of functional fluorescent dendrimer
materials.

\begin{scheme*}
\vspace*{3pt}
\includegraphics{sc10}
\vspace*{5pt}
\caption{\label{sch10}Chemical structures of dendrimers \textbf{44} and
\textbf{45} peripherally modified with four 4-sulfo-1,8-naphthalimide
units.}
%\vspace*{-10pt}
\end{scheme*}

In contrast to hydrophobic fluorescent dendrimers, water-soluble
dendrimers require careful selection of both the dendrimer matrix and
the fluorophoric units, as well as the mode of their attachment to the
dendrimer. Water solubility can be achieved by introducing negatively
charged anionic groups, such as carboxyl (--COOH) or sulfonic
(--SO\tsub{3}H) groups, into the 1,8-naphthalimide structure, by
quaternization of amino groups, or by incorporating substituents
containing polar functionalities, such as hydroxyl groups in
$N$-glucosamine derivatives. In this manner, the charge of the
dendrimers can be controlled by selecting appropriate functional
groups. This strategy allows fine-tuning of macromolecular properties
and provides a means of regulating interactions between dendrimers and
their surrounding environment. At the same time, retention of
fluorophores at the dendrimer periphery ensures good accessibility and
minimizes undesirable intramolecular interactions that could lead to
fluorescence quenching.

The synthesis of 4-sulfo-1,8-naphthalimide-modified first-generation
PPI (G1) and zero-generation PAMAM (G0) dendrimers was designed to
enhance the hydrophilicity of the resulting macromolecules and was
carried out in a one-step reaction of the potassium salt of
4-sulfo-1,8-naphthalic anhydride with the corresponding dendrimers 
(Scheme~\ref{sch10}). The resulting dendrimers absorb in the
ultraviolet region and emit blue  fluorescence~\cite{89,90}.

The presence of carboxyl groups (--COOH) on a PAMAM dendrimer was
achieved via a one-step synthesis by reacting
3-(6-nitro-1,3-dioxo-1H-benzo[de]isoquinolin-2(3H)-yl)propanoic acid
with the terminal amino groups of the dendrimer in DMF at
25~\textdegree C. The structure of dendrimer \textbf{46} is presented
in Scheme~\ref{sch11}; it exhibits yellow--green fluorescence, as
reported in Ref.~\cite{91}.

\begin{scheme*}
\includegraphics{sc11}
\vspace*{6pt}
\caption{\label{sch11}Chemical structures of a PAMAM dendrimers bearing
carboxyl groups \textbf{(46)} and PPI dendrimers containing
$N$-glucosamine units  \textbf{(47)}.}
\vspace*{-8pt}
\end{scheme*}

Dendrimers modified with $N$-glucosamine have attracted considerable
interest in nanomedicine due to their unique multivalent architecture
and ability to neutralize the high positive charge of parent
dendrimers, such as PPI and PAMAM. This charge compensation leads to
improved biocompatibility and reduced cellular toxicity. Such
dendrimers can act as ``smart'' carriers, capable of simultaneously
transporting drug molecules while also exhibiting intrinsic biological 
activity~\cite{92,93,94}.

In our studies,  $N$-glucosamine was combined with 1,8-naphthalimide to
modify a first-generation poly(propylene imine) (PPI) dendrimer
\textbf{47}  (Scheme~\ref{sch11}), resulting in significantly improved
water solubility of the PPI  dendrimer~\cite{95}.

To introduce a quaternary ammonium group into the structure of a PPI
dendrimer, the primary amino group of dendrimer \textbf{29} was first
acylated with chloroacetyl chloride to afford dendrimer \textbf{48}.
Subsequently, the chlorine atom was substituted by reaction with
pyridine, yielding dendrimer \textbf{49} with a quaternary ammonium
group. As a consequence of introducing the electron-accepting acylated
amino group, the fluorescence emission shifted from yellow--green
(dendrimer \textbf{29}) to blue, while the quaternary ammonium group
imparted excellent water solubility to the resulting dendrimer 
(Scheme~\ref{sch12})~\cite{96}.

\begin{scheme}
\includegraphics{sc12}
\vspace*{5pt}
\caption{\label{sch12}Synthesis of a water-soluble PPI dendrimer
\textbf{49} modified with a quaternized 4-amino-1,8-naphthalimide.}
\vspace*{-10pt}
\end{scheme}

\section{Photoactive dendrimers for application in antibacterial
photodynamic therapy (aPDT)}\label{sec4}
Specialized photoactive dendrimers represent a logical extension of the
concept of fluorescent dendrimers, in which macromolecular design is
directed not only toward fluorescence emission but also toward the
control of photoinduced processes. In such systems, the dendrimer
architecture serves as a platform for spatially organizing photoactive
centers, enabling purposeful modulation of their properties through
chemical modification.

In our studies, particular attention has been devoted to introducing
heavy atoms into the fluorophore structure as an effective tool for
tuning the photophysical characteristics of dendrimer systems. For the
first time, dendrimers peripherally modified with brominated
4-amino-1,8-naphthalimide units were synthesized, in which the heavy
atom was introduced directly into the chromophoric system at the C-3
position. The presence of a bromine atom in the fluorophore structure
exerts a pronounced influence on the photoactivity of the dendrimer.

Bromine can enhance spin--orbit coupling within fluorophore molecules,
thereby increasing the rate of intersystem crossing (ISC) from the
singlet excited state (S\tsub{1}) to the triplet state (T\tsub{1}). This
phenomenon is known as the \textit{heavy atom effect}~\cite{97}. The
enhancement of ISC is directly related to the efficiency of singlet
oxygen  (\tsup{1}{O}\tsub{2})  generation~\cite{98,99,100}. In
this context, the introduction of a bromine atom constitutes a key
innovation and is essential for achieving antimicrobial photodynamic
activity in 1,8-naphthalimide-based systems.

To obtain dendrimers modified with 1,8-naphthalimide units bearing both
a bromine atom and an amino substituent, a first-generation PPI
dendrimer peripherally modified with 4-nitro-1,8-naphthalimide units
(\textbf{25}) was employed as a precursor. The nitro group was replaced
by an  $N$,$N$-dimethylamino group via electrophilic substitution to
yield dendrimer \textbf{50}, followed by bromination with molecular
bromine to introduce the bromine atom, affording dendrimer \textbf{51} 
(Scheme~\ref{sch13})~\cite{101}. Compared to the non-brominated
fluorescent dendrimer \textbf{50}, dendrimer \textbf{51} exhibits
altered photophysical behavior, which is attributed to enhanced ISC and
modified deactivation pathways of the excited state. These results
demonstrate the potential of dendrimers for the rational design of
systems with controlled photoactivity.

\begin{scheme*}
\vspace*{3pt}
\includegraphics{sc13}
\vspace*{5pt}
\caption{\label{sch13}Synthesis of PPI dendrimers \textbf{50} and
\textbf{51}.}
\vspace*{10pt}
\end{scheme*}

\section{Synthesis of  fluorescent hyperbranched polymers modified with
fluorophores}\label{sec5}
Hyperbranched polymers (HBPs) constitute a distinct class of branched
macromolecules characterized by a high degree of branching and a large
number of terminal functional groups. In contrast to dendrimers, HBPs
are obtained through statistical \mbox{polymerization} processes and therefore
do not possess strictly defined, monodisperse structures. Nevertheless,
they combine several key advantages of dendrimers such as their
three-dimensional architecture and multivalency with a simpler, more
cost-effective synthetic  approach~\cite{102,103,104}.

In this review, HBPs are considered an alternative platform for the
development of fluorescent branched systems closely related to
dendrimer design. Within our studies, fluorescent HBPs modified with
organic fluorophores were synthesized employing synthetic strategies
analogous to those applied for dendrimers. Their preparation involves
the chemical modification of a commercially available hyperbranched
polyesteramide  (Hybrane\tsup{\text{\textregistered}} P 1000, HBP--OH),
containing multiple hydroxyl groups, 
\mbox{followed} by the introduction of
azide functionalities suitable for subsequent covalent attachment of
fluorophores via click chemistry. This modification does not alter the
hyperbranched architecture of the polymer but generates an
azide-functionalized HBP that can serve as a versatile platform for the
incorporation of photoactive units of different chemical nature 
(Scheme~\ref{sch14}).

\begin{scheme*} 
\includegraphics{sc14}
\vspace*{5pt}
\caption{\label{sch14}Schematic representation of the synthesis of
fluorescent hyperbranched polymers based on 
Hybrane\tsup{\text{\textregistered}} P 1000 via azide functionalization
and subsequent Cu(I)-catalyzed click attachment of fluorophores.}
\vspace*{-8pt}
\end{scheme*}

Fluorophores such as 1,8-naphthalimides~\cite{105}, dansyl 
derivatives~\cite{106}, and acridines~\cite{107} were employed, each
modified to contain a terminal alkyne group. This structural
modification renders the fluorophore molecules ``click-active''
components, capable of selectively reacting with the azide groups of
the polymer to form stable 1,2,3-triazole rings that serve as covalent
linkages between the fluorophores and the polymer backbone. The number
of incorporated fluorophore units is controlled by the predefined
number of azide groups present on the polymer platform. In the
investigated systems, this strategy resulted in polymers bearing six
covalently attached fluorophores per macromolecule 
(Scheme~\ref{sch15}).

\begin{scheme*}
\vspace*{2pt}
\includegraphics{sc15}
\vspace*{4pt}
\caption{\label{sch15}Chemical structures of the modified photoactive
HBPs \textbf{52}--\textbf{54}.}
\vspace*{-6pt}
\end{scheme*}

Comparison between fluorescent dendrimers and hyperbranched polymers
highlights both similarities and fundamental differences between these
two types of branched systems. While dendrimers offer precise control
over architecture and fluorophore distribution, hyperbranched polymers
provide enhanced synthetic accessibility and scalability. In both
cases, peripheral fluorophore modification yields photoactive
macromolecules, in which the branched structure plays a crucial role in
determining their photophysical properties.

The first syntheses presented of fluorescent HBPs demonstrate that
these systems can successfully complement dendrimer-based architectures
in the development of new fluorescent materials. The relationship
between dendrimers and hyperbranched polymers underscores the
universality of the applied synthetic approaches and expands the
possibilities for designing branched photoactive macromolecules with
diverse structural characteristics.

The differences between the three fluorescent hyperbranched polymers
arise from the chemical nature of the incorporated fluorophores rather
than from the mode of their attachment to the polymer backbone. This
confirms the universality of the applied synthetic approach and enables
direct 
\mbox{comparison} of the functional properties of the resulting
polymeric systems.

\section{Influence of substituents and dendrimer generation on the
photophysical properties}\label{sec6}
The photophysical properties of dendrimers modified with
1,8-naphthalimide chromophores depend both on the nature of the
substituents at the C-4 position of the naphthalimide core and on the
\mbox{dendrimer} architecture. It has been found that the spectral
characteristics of these systems depend mainly on the electron-donating
ability of the substituents at the C-4 position, whereas substituents
attached to the imide nitrogen have only a negligible effect.

Primary and secondary amino substituents at the C-4 position form
effective \mbox{donor--acceptor} 
\mbox{interactions,} resulting in strong
fluorescence emission, usually in the yellow--green 
region~\cite{44,61,62,64,66,69}. In contrast, cyclic or acyclic
tertiary amino groups 
often lead to reduced fluorescence intensity due
to conformational effects that disrupt the planarity of the chromophore
and promote non-radiative deactivation  pathways~\cite{45,77}.
Alkoxy-substituted 1,8-naphthalimides represent another important class
of fluorophores. Their weaker electron-donating character, compared to
amino substituents, induces hypsochromically shifted spectra and blue
fluorescence  emission~\cite{60,67,74}.

Of particular interest are systems containing remote tertiary amino
groups linked to the chromophore via ethylamino or ethoxy 
spacers~\cite{44,60,66,67,68,74,76}. In these systems, fluorescence
intensity shows a pronounced dependence on solvent polarity due to
photoinduced electron transfer (PET). In polar media, PET processes
favor fluorescence quenching, whereas in less polar solvents the
emission is enhanced.

Brominated 1,8-naphthalimide derivatives represent an additional
structural motif influencing photophysical behavior. The introduction
of a bromine atom at the C-3 position induces a hypsochromic shift of
both the absorption and fluorescence maxima and generally reduces
fluorescence quantum yields, reflecting the heavy-atom effect and
altered chromophore polarization. At the same time, bromination
facilitates ISC and population of triplet states, features particularly
important for photodynamic  applications~\cite{101}.

In addition to substituent effects, dendrimer 
architecture introduces
an additional level of control over photophysical behavior. The
modified dendrimers contain different numbers of fluorophores, which in
most cases retain the photophysical properties of the corresponding
monomers without significant self-quenching. As a manifestation of the
dendrimer effect, increased molar absorptivity was observed for all
synthesized dendrimers, proportional to the number of peripherally
attached chromophores.

This indicates that the dendrimer structure can provide sufficient
spatial separation between chromophore units while minimizing
aggregation, although at higher generations or in systems bearing bulky
substituents, partial interchromophoric interactions may occur. Both
dendrimer backbone structure and solvent polarity influence the
photophysical properties of the modified dendrimers. Structural
differences between PAMAM and PPI dendrimers affect the local
microenvironment of the chromophores, including polarity,
conformational flexibility, and possible intramolecular interactions,
which can alter emission intensity and spectral 
\mbox{position.}

Overall, the photophysical properties of 1,8-naphthalimide-modified
dendrimers result from the combined influence of substituent effects
and dendrimer architecture. The interplay of these factors provides a
basis for the rational design of fluorescent macromolecular systems
with tailored optical characteristics.

\section{Brief overview of biological and sensing properties of
fluorescent dendrimers}\label{sec7}

\subsection{Sensor activity of dendrimers modified with
1,8-naphthalimides}\label{sec7.1}
These structure--photophysical relationships are directly reflected in
the sensing behavior of the systems, as discussed in the following 
section. The fluorescent dendrimers developed within the scope of the
studies presented demonstrate significant potential for applications in
sensing systems, with these properties being directly related to the
synthetic design and architectural features of the macromolecules. The
branched structure, multivalent periphery, and controlled fluorophore
functionalization create favorable conditions for effective
interactions with analytes, including metal ions, protons, and
biological  targets~\cite{24}. The sensing properties of fluorescent
dendrimers originate from the ability to modulate the photophysical
characteristics of the fluorophores in response to changes in the
surrounding environment or the presence of specific analytes.
Peripheral localization of the photoactive units facilitates direct
access of the analytes to the fluorophore centers and allows measurable
variations in the fluorescence signal. In this context, the dendrimer
architecture does not merely serve as a carrier but actively
contributes to the amplification and stabilization of the sensing
response. A commonly employed strategy for constructing fluorescent
dendrimer-based sensors involves modifying PPI or PAMAM dendrimers with
fluorophores containing donor--acceptor systems, such as
1,8-naphthalimide derivatives bearing receptor fragments. In these
systems, the fluorophore serves as the signaling unit, while peripheral
or internal functional groups act as receptor sites for metal cations
or  protons~\cite{24}. The sensing mechanism is most frequently based
on PET which leads to fluorescence quenching or enhancement depending
on the presence of the  analyte~\cite{50}. Coordination of a metal ion
or protonation of donor atoms reduces their electron-donating ability
and suppresses PET, thereby restoring or 
\mbox{enhancing} the fluorescence
signal. For example, dendrimers containing tertiary amine receptor
groups exhibit fluorescence enhancement upon coordination with
Pb\tsup{2+} ions, while Cu\tsup{2+} ions can induce efficient quenching due
to complex formation within the dendrimer 
structure~\cite{24,59,74,75}. Similar behavior has been observed in a
number of systems based on 1,8-naphthalimide-modified dendrimers, where
fluorescence modulation upon interaction with metal ions such as
Zn\tsup{2+}, Fe\tsup{3+}, and Li\tsup{+} has been 
reported~\cite{63,65,69,108}. More recent studies on water-soluble
systems demonstrate pronounced selectivity toward Cu\tsup{2+} ions in
aqueous media, even in the presence of competing ions, confirming their
applicability as selective fluorescent  sensors~\cite{90}. The
dendrimer architecture enables the simultaneous participation of
multiple receptor sites and fluorophore units, leading to high
sensitivity and, in some cases, pronounced selectivity toward specific
metal ions. It has been shown that coordination of even a single metal
ion within the dendrimer matrix can induce a significant change in the
fluorescence response, highlighting the advantages of the multivalent
dendrimer  effect~\cite{69,109}. In addition to metal ion detection,
fluorescent dendrimers have also been employed as proton sensors, in
which changes in the medium's acidity result in distinct spectral and
colorimetric variations. For instance, protonation of internal amino
groups suppresses PET processes and leads to enhanced fluorescence
emission, whereas deprotonation restores PET and results in
fluorescence  quenching~\cite{90}. This enables their use as
fluorimetric and colorimetric pH sensors in organic solvents and
heterogeneous systems. Compared to their low-molecular-weight analogs,
dendrimer-based sensors exhibit enhanced sensitivity, tunable
selectivity achieved through molecular design, and the potential for
integration into heterogeneous materials and composite systems. These
features establish fluorescent dendrimers as promising platforms for
the development of sensing materials for metal ions and 
protons~\cite{24}.

\subsection{Antibacterial and photodynamic\newline
activity of dendrimers
modified with\newline 
1,8-naphthalimides}\label{sec7.2}
Fluorescent dendrimers represent a promising class of antimicrobial
agents in which biological activity arises from the combined effect of
the dendrimer architecture and the incorporated photoactive
fluorophores. The multivalent nature of dendrimers enables efficient
interactions with microbial cell membranes, particularly in systems
possessing cationic or amphiphilic surfaces, leading to membrane
destabilization and cellular dysfunction, as widely described for
antimicrobial  dendrimers~\cite{110}.

The antibacterial activity of dendrimers modified with
1,8-naphthalimide derivatives is governed by a complex interplay
between the dendrimer architecture, the nature of the substituents at
the C-4 position of the chromophore, and the presence of metal ions or
light  activation~\cite{78,101,111,112,113}. In these systems, the
dendrimer acts not only as a carrier but also as an active structural
element that enhances the local concentration of photoactive units and
promotes interactions with microbial targets. From a
structure--activity relationship perspective, the nature of the C-4
substituent plays a decisive role by modulating the electron-donating
ability, fluorescence efficiency, and capacity for photoinduced
electron transfer, which in turn directly influences both sensing and
antimicrobial performance.

The basic antimicrobial mechanism involves interactions with the
bacterial membrane, followed by disruption of its integrity and
increased permeability. This effect is more pronounced for
Gram-positive bacteria, while Gram-negative strains exhibit higher
resistance due to the presence of an outer  membrane~\cite{48,49}. In
addition, experimental studies show that modified dendrimers can bind
to and penetrate bacterial membranes, facilitating subsequent
photodynamic action.

Complexation with metal ions, particularly Cu(II), significantly
enhances antimicrobial efficiency. For example, a PAMAM dendrimer
modified with 1,8-naphthalimide units and its copper complex exhibit
stronger antibacterial activity than the corresponding ligand, with
minimum inhibitory concentrations (MIC) as low as 6.96~$\upmu$M against
\textit{Bacillus cereus} under light  irradiation~\cite{61}. The
increased activity of the metallodendrimer is attributed to both
improved membrane interactions and enhanced generation of reactive
oxygen species  (ROS)~\cite{61}.

Photoactive dendrimers show a pronounced increase in antimicrobial
activity upon light irradiation. Under illumination, these systems
generate ROS, predominantly singlet oxygen 
(\tsup{1}{O}\tsub{2}), which 
\mbox{induces} oxidative damage to
bacterial membranes and intracellular components. Quantitative
experiments demonstrate that bacterial growth inhibition can increase
from approximately 50\% in the dark to over 80\% under light
irradiation for metallodendrimer systems. This synergistic effect
between intrinsic antimicrobial properties and photodynamic activity
makes these systems highly effective for antimicrobial photodynamic
therapy\unskip\break  
(aPDT)~\cite{101,113}.

Furthermore, the ability of these dendrimers to generate singlet oxygen
is preserved after immobilization onto solid substrates. Dendrimers
deposited onto cotton fabrics retain their photodynamic activity and
exhibit strong antibacterial effects under irradiation, leading to
nearly complete inhibition of bacterial growth in some cases. This
enables the development of functional self-disinfecting materials and
textile-based antimicrobial  systems~\cite{114,115}.
\looseness=1

In addition to dendrimers, structurally related hyperbranched polymers
exhibit similar behavior, combining multivalency and photodynamic
activity, which further broadens the range of applications of such 
systems~\cite{62}. Overall, dendritic and hyperbranched architectures
functionalized with 1,8-naphthalimide units provide an effective
platform for the design of multifunctional antimicrobial systems, in
which membrane interactions, metal ion effects, and photodynamic
mechanisms act synergistically to enhance biological performance.

\section{Conclusions and outlook}\label{sec8} 
This review summarizes our systematic research on the synthesis of
fluorescent dendrimers and other branched polymers based on peripheral
modification with organic fluorophores. The main emphasis is on
applying universal synthetic approaches to prepare well-defined
branched macromolecules with tunable photophysical properties. In our
work, a series of fluorescent poly(amidoamine) and poly(propylene
imine) dendrimers modified with different classes of fluorophores,
including 1,8-naphthalimides, brominated naphthalimides, benzanthrone,
acridine, and 4-nitrobenzofurazan, has been reported. It has been shown
that dendrimer architecture, together with the nature of the
fluorophore substituents, plays a key role in 
\mbox{controlling} the spatial
distribution of photoactive groups and their photophysical behavior,
enabling targeted study of structure--property relationships. The first
examples of fluorescent hyperbranched polymers obtained via synthetic
strategies inspired by dendrimer design are also presented. The
comparison between strictly defined dendrimers and statistically
branched polymers highlights both the advantages of dendrimer
architecture for structural control and the practical advantages of
hyperbranched systems for synthetic accessibility and efficiency.
Water-soluble fluorescent dendrimers showed potential in adapting to
specific environmental conditions without compromising structural
integrity. In addition to their sensing potential, the fluorescent
dendrimers presented exhibit antimicrobial photodynamic activity
directly related to molecular design, peripheral functionalization, and
the photoactivity of the incorporated fluorophores. The combined
influence of substituent effects, dendrimer generation, and multivalent
architecture provides versatile opportunities for tuning photophysical
properties and functional performance.

Future perspectives include expanding the diversity of fluorophore
systems, achieving finer control over dendrimer architecture and
photophysical behavior, and integrating photoactivity with additional
functional properties, particularly sensing and antimicrobial
photodynamic activity.

In conclusion, peripheral modification of dendrimers and hyperbranched
polymers with organic fluorophores represents a versatile strategy for
designing photoactive macromolecules with tunable optical properties
and promising applications in sensing, biomedicine, and functional
materials.

\section*{Funding} 
This study is financed by the European Union Next Generation EU,
through the National Recovery and Resilience Plan of the Republic of
Bulgaria, project No~BG-RRP-2.004-0008 and European Union Next
Generation EU, through the National Recovery and Resilience Plan of the
Republic of Bulgaria, project No~BG-RRP-2.004-0002, ``BiOrgaMCT'',
European Union (Nextgeneration EU), through CSIC Interdisciplinary
Thematic Platform Salud Global$+$ (PTI-SALUDGLOBAL$+$). 

\CDRGrant[EU]{BG-RRP-2.004-0008}
\CDRGrant[EU]{BG-RRP-2.004-0002}

\printCOI

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\end{document}