\makeatletter \@ifundefined{HCode} {\documentclass[screen,CRCHIM,Unicode]{cedram} \newenvironment{noXML}{}{} \def\tsup#1{$^{{#1}}$} \def\tsub#1{$_{{#1}}$} \def\thead{\noalign{\relax}\hline} \def\tbody{\noalign{\relax}} \def\endthead{\noalign{\relax}\hline} \def\botline{\\\hline} \def\ndash{\text{--}} \RequirePackage{etoolbox} \def\jobid{crchim20240466} %\graphicspath{{/tmp/\jobid_figs/web/}} \graphicspath{{./figures/}} \newcounter{runlevel} \let\MakeYrStrItalic\relax \csdef{Seqnsplit}{\\} \def\refinput#1{} \def\back#1{} \def\rmDelta{\Delta} \def\rmLambda{\Lambda} \def\rmPhi{\Phi} \def\rmalpha{\upalpha} \def\sfrac#1#2{{#1}/{#2}} \def\sbfrac#1#2{{#1}/{(#2)}} \def\0{\phantom{0}} \def\mn{\phantom{$-$}} \def\ubreak{\break} \newenvironment{inftab}{}{} \usepackage{multirow} \def\nrow#1{\@tempcnta #1\relax% \advance\@tempcnta by 1\relax% \xdef\lenrow{\the\@tempcnta}} \def\morerows#1#2{\nrow{#1}\multirow{\lenrow}{*}{#2}} \DOI{10.5802/crchim.364} \datereceived{2024-06-06} \daterevised{2024-10-07} \dateaccepted{2024-11-19} \ItHasTeXPublished } {\documentclass[crchim]{article} \def\0{\phantom{0}} \def\CDRdoi{10.5802/crchim.364} \def\sfrac#1#2{{#1}/{#2}} \def\sbfrac#1#2{{#1}/{(#2)}} \let\newline\break \let\ubreak\relax \makeatletter \def\CDRsupplementaryTwotypes#1#2{} } \makeatother %\copyeditor{RB} \usepackage{upgreek} \begin{document} \begin{noXML} \CDRsetmeta{articletype}{research-article} \title{Photophysical studies of Zn(II) tetra, \textit{tert-butyl} phthalocyanine} \alttitle{\'{E}tudes photophysiques de la T\'{e}trakis(\textit{tert}-butyl)phthalocyanine de Zn(II)} \author{\firstname{Sami} \lastname{Ayari}\CDRorcid{0000-0002-1505-1922}\IsCorresp} \address{Universit\'{e} de Lorraine, CNRS, LRGP, F-54000 Nancy, France} \address{Laboratoire Microorganismes et Biomol\'{e}cules Actives, LR03ES03, Universit\'{e} de Tunis El Manar, Facult\'{e} des Science de Tunis, 2092, Campus Universitaire, Tunis, Tunisie} \email[S. Ayari]{sami.ayari@fst.utm.tn} \author{\firstname{Philippe} \lastname{Arnoux}\CDRorcid{0000-0002-6834-9597}} \addressSameAs{1}{Universit\'{e} de Lorraine, CNRS, LRGP, F-54000 Nancy, France} \author{\firstname{Hadda Imene} \lastname{Ouzari}\CDRorcid{0000-0002-3237-554X}} \addressSameAs{2}{Laboratoire Microorganismes et Biomol\'{e}cules Actives, LR03ES03, Universit\'{e} de Tunis El Manar, Facult\'{e} des Science de Tunis, 2092, Campus Universitaire, Tunis, Tunisie} \author{\firstname{C\'eline} \lastname{Frochot}\CDRorcid{0000-0002-7659-3864}\IsCorresp} \addressSameAs{1}{Universit\'{e} de Lorraine, CNRS, LRGP, F-54000 Nancy, France} \email[C. Frochot]{celine.frochot@univ-lorraine.fr} \shortrunauthors \keywords{\kwd{UV--vis absorption} \kwd{\textit{tert}-ZnPc(II)} \kwd{Photophysical properties}} \altkeywords{\kwd{Absorption UV--vis} \kwd{\textit{tert}-ZnPc(II)} \kwd{Propri\'{e}t\'{e}s photophysiques}} \thanks{French Institute of Tunisia} \begin{abstract} Phthalocyanine derivatives have attracted significant attention due to their unique chemical properties and applications in various fields, including photodynamic therapy. However, the synthesis and purification of phthalocyanines remain challenging. Among these derivatives, zinc(II) tetra, \textit{tert}-\textit{butyl} phthalocyanine (\textit{tert}-ZnPc(II)) is noteworthy for its straightforward synthesis, making it a cost-effective option. \textit{tert}-ZnPc(II) is often synthesized as a second-generation byproduct in the synthesis of asymmetric phthalocyanines when \textit{tert}-butyl moieties are introduced to enhance the solubility of derivatives in a wide range of organic solvents. The practical applications of phthalocyanine derivatives depend mainly on their photophysical properties, which in turn influence key parameters such as absorption and fluorescence emission. This study investigates the ultraviolet--visible (UV--vis) absorption and fluorescence emission spectroscopies of \textit{tert}-ZnPc(II), focusing on the impact of solvent polarity and the effect of different concentrations of water on UV--vis absorption behavior. \end{abstract} \begin{altabstract} Les d\'{e}riv\'{e}s de phtalocyanine ont suscit\'{e} un int\'{e}r\^{e}t consid\'{e}rable en raison de leurs propri\'{e}t\'{e}s chimiques uniques et de leurs applications dans divers domaines, notamment la th\'{e}rapie photodynamique (PDT). Cependant, la synth\`{e}se et la purification des phtalocyanines restent difficiles. Parmi ces d\'{e}riv\'{e}s, la phtalocyanine de zinc(II) t\'{e}tra-\textit{tert}-butyle (\textit{tert}-ZnPc(II)) se distingue par sa synth\`{e}se simple, en faisant une option rentable. Le \textit{tert}-ZnPc(II) est souvent synth\'{e}tis\'{e} comme sous-produit de deuxi\`{e}me g\'{e}n\'{e}ration lors de la synth\`{e}se de phtalocyanines asym\'{e}triques, lorsque des groupes \textit{tert}-butyles sont introduits pour am\'{e}liorer la solubilit\'{e} des d\'{e}riv\'{e}s dans une large gamme de solvants organiques. Les applications pratiques des d\'{e}riv\'{e}s de phtalocyanine d\'{e}pendent principalement de leurs propri\'{e}t\'{e}s photophysiques, qui influencent \`{a} leur tour des param\`{e}tres cl\'{e}s tels que l'absorption et l'\'{e}mission de fluorescence. Cette \'{e}tude examine les spectroscopies d'absorption UV--visible et d'\'{e}mission de fluorescence du \textit{tert}-ZnPc(II), en se concentrant sur l'impact de la polarit\'{e} du solvant et sur l'effet de diff\'{e}rentes concentrations d'eau sur le comportement d'absorption UV--vis. \end{altabstract} \maketitle \vspace*{11pt} \twocolumngrid \end{noXML} \section{Introduction} Phthalocyanines (Pcs) and their derivatives represent aromatic macrocycles with an 18-${\uppi}$-electron delocalization system characterized by high chemical and thermal stability. These compounds possess diverse coordination properties, exhibit low toxicity, and have the ability to absorb within the visible region (600--800~nm). The versatility of Pcs is featured in a wide range of applications~\cite{1,2,3,4,5}, such as semiconductor devices~\cite{6}, liquid crystals~\cite{7,8,9}, sensors~\cite{10,11,12}, catalysts~\cite{13}, and dye-sensitized solar cells~\cite{14,15}. Furthermore, Pcs have emerged as highly promising photosensitizers in the context of photodynamic therapy (PDT)~\cite{16,17,18,19,20,21,22}. The photophysical characteristics of Pcs are notably influenced by the central metal ion, with zinc (Zn) proving particularly valuable due to its ability to confer Pcs with enhanced fluorescence and singlet oxygen production properties. These attributes make them suitable for applications in tumor detection and treatment~\cite{23}. The solubility of Pcs is a pivotal factor for diverse applications. Introducing functional groups such as alkyl, tertiary butyl groups, crown ethers, alkoxy, alkylthio, and amide groups into peripheral benzene rings of the Pc structure enhances solubility in both protic and non-protic solvents~\cite{24,25,26,27,28,29,30,31,32}. Notably, water solubility assumes a crucial role in PDT applications~\cite{33,34,35}. While sulfonates~\cite{36},\unskip\break carboxylates~\cite{37,38}, and quaternized amino groups~\cite{39,40,41} are commonly employed to achieve water solubility in dyes, \textit{tert}-butyl groups confer Pcs with hydrophobic properties~\cite{42}. An important consideration in the study of Pcs is their tendency to form aggregates, especially in aqueous solutions~\cite{43}. This property proves unfavorable as it reduces solubility and adversely impacts photophysical characteristics, such as shortening the triplet state lifetime and hindering the efficient generation of singlet oxygen. In the context of in vivo activity as photosensitizers, aggregation not only diminishes photoactivity but also restricts access to neoplastic cells~\cite{44}. The degree of this effect is significantly influenced by the molecular structure, particularly the nature of the central metal ion and functional groups present in the peripheral substituents~\cite{45,46}. Since photochemical activity is important only for Pc monomers, assessing aggregation parameters becomes essential for accurately determining the photophysical properties of these compounds. The formation of aggregates is primarily driven by ${\uppi}\ndash {\uppi}$ stacking between the nearly planar Pc macrocycles and van der Waals forces. Depending on their geometry, H-type (sandwich) and J-type (head-to-tail) aggregates can be distinguished, exhibiting significant differences in optical properties according to Kasha's exciton model~\cite{47,48}. Considering the cost-effectiveness and commercial availability of \textit{tert}-ZnPc(II), it emerges as an intriguing compound with a vast field of applications. In this study, we aim to explore the impact of solvent polarity on the photophysical properties (absorption and fluorescence emission spectroscopies) of \textit{tert}-ZnPc(II). This work explores its photophysical properties, with special attention given to the effect of different concentrations of water on absorption behavior and aggregation in homogeneous\unskip\break solutions. \section{Results and discussion} The most important properties of Pcs as materials lie in their exceptional thermal, chemical, and photochemical stabilities. Typically, unsubstituted Pc complexes exhibit low solubility across a wide range of solvents. Solubility in organic solvents is crucial for exploring the diverse applications of these molecules. Enhancing solubility in water or common organic solvents can be effectively achieved through peripheral modifications of Pcs, particularly by introducing the right substitutions on benzene rings\unskip\break \cite{49a,49b,49c}. In contrast to unsubstituted Pc metal complexes, \textit{tert}-ZnPc(II), despite existing as a mixture of four positional isomers~\cite{50a,50b,51a,51b,51c,51d}, stands out due to the incorporation of bulky \textit{tert}-butyl substituents. This modification mitigates the aggregation tendencies of Pcs and enables an increase in their solubility across various common organic solvents without causing a significant shift in their ultraviolet--visible (UV--vis) spectra~\cite{52}. The chemical structure of \textit{tert}-ZnPc(II) is shown in Figure~\ref{fig1}. \begin{figure} \includegraphics{fig01} \vspace*{-4pt} \caption{\label{fig1}Chemical structure of \textit{tert}-ZnPc(II).} \vspace*{-2pt} \end{figure} \vspace*{-2pt} \subsection{Effect of the solvent} \vspace*{-2pt} \subsubsection{Ground-state electronic absorption spectra} The photophysical characteristics of Pc macrocycles are primarily influenced by their molecular structure and their interaction with the surrounding environment~\cite{53}. The UV--vis absorption spectra of \textit{tert}-ZnPc(II), as illustrated in Figure~\ref{fig2}, were measured in various solvents. Solvent polarity is quantified by the $\mathrm{E}_{\mathrm{T}}$(30) parameter, with higher $\mathrm{E}_{\mathrm{T}}$(30) values indicating increased solvent polarity ($\mathrm{E}_{\mathrm{T}}$(30) water ${=}$ 63.1, $\mathrm{E}_{\mathrm{T}}$(30) glycerol ${=}$ 57, $\mathrm{E}_{\mathrm{T}}$(30) methanol ${=}$ 55.4, $\mathrm{E}_{\mathrm{T}}$(30) ethanol ${=}$ 51.9, $\mathrm{E}_{\mathrm{T}}$(30) acetonitrile ${=}$ 45.6, $\mathrm{E}_{\mathrm{T}}$(30) DMF ${=}$ 43.8, $\mathrm{E}_{\mathrm{T}}$(30) chloroform ${=}$ 39.1, $\mathrm{E}_{\mathrm{T}}$(30) ethyl acetate ${=}$ 38.1, $\mathrm{E}_{\mathrm{T}}$(30) toluene ${=}$ 33, $\mathrm{E}_{\mathrm{T}}$(30) FBS ${=}$ unknown)~\cite{54,55}. \begin{figure} \includegraphics{fig02} \caption{\label{fig2}Absorption spectra of \textit{tert}-ZnPc(II) in 10 different solvents ($7.5\times 10^{-6}~\mathrm{mol}{\cdot}\mathrm{L}^{-1}$).} \vspace*{-1pt} \end{figure} A DMSO stock solution ($\mathrm{m}_{\mathit{tert}\text{-ZnPc} (\mathrm{II})} = 4.75~\mathrm{mg}$, $\mathrm{V}_{\mathrm{DMSO}} = 4.75~\mathrm{mL}$) was prepared, ensuring compound solubility. This stock solution was further diluted in 10 different solvents to investigate the specific impact of solvent polarity on photophysical properties. Concentration standardization was achieved in toluene by adjusting the peak absorbance at 610~nm to approximately 0.2, equivalent to $6\times 10^{-3}~\mathrm{mg}{\cdot}\mathrm{mL}^{-1}$. The solvents include toluene, ethyl acetate, ethanol, methanol, DMF, acetonitrile, chloroform, glycerol, water, and a 10\% dilution of fetal bovine serum (FBS) in a biological medium. The absorption spectra are presented in Figure~\ref{fig2}. The pronounced tendency of Pcs to form dimers and trimers in solution leads to a reduction in its photoactivity as a photosensitizer. This is attributed to the fact that the monomer structure is responsible for optimal photochemical activity~\cite{44,45,46}. In Figure~\ref{fig2}, the absorption spectra of \textit{tert}-ZnPc(II) in toluene, ethyl acetate, ethanol, methanol, DMF, and acetonitrile are depicted. The Soret and Q bands exhibit consistent shapes with minor shifts, aligning with the characteristic UV--vis spectra of Pcs. On the other hand, absorption spectra of \textit{tert}-ZnPc(II) in chloroform, glycerol, water, and FBS show a significant alteration in the shape, intensity, and split absorption peaks in comparison to the spectra in toluene, indicating an aggregation effect. \textit{tert}-ZnPc(II) exhibits two main absorption bands at 350~nm and 610~nm. These bands exhibit diminished intensity in aqueous medium, glycerol, and chloroform, coupled with a red shift. Conversely, the spectra appear quite similar in the other\break solvents. The molar extinction coefficient (${\upvarepsilon}$) is an intrinsic property of molecules depending mostly on their structure and composition. It assesses how chemical species absorb photons at specific wavelengths. The molar extinction coefficients of \textit{tert}-ZnPc(II) are calculated and depicted in Table~\ref{tab1}. \begin{table*} \caption{\label{tab1}Absorbance B and Q bands and molar extinction coefficient of \textit{tert}-ZnPc(II) in different solvents\vspace*{-1pt}} \begin{tabular}{cccccc} \thead Solvents & B band (nm) & Q band 1 (nm) & Q band 2 (nm) & ${\upvarepsilon}$350 & ${\upvarepsilon}$610 \\ \endthead Toluene & 350 & 610 & 676 & 56,802 & 29,403 \\ Ethyl acetate & 347 & 606 & 671 & 60,277 & 28,067 \\ Ethanol & 347 & 608 & 674 & 57,738 & 28,067 \\ Methanol & 346 & 608 & 673 & 55,064 & 27,933 \\ DMF & 349 & 609 & 675 & 61,079 & 31,675 \\ Acetonitrile & 346 & 606 & 672 & 56,535 & 27,933 \\ Chloroform & 357 & 679 & 718 & 30,740 & 11,494 \\ Glycerol & 349 & 633 & 685 & 17,776 & 12,162 \\ Water & 338 & 630 & 678 & 37,422 & 25,527 \\ FBS & 339 & 630 & 679 & 45,174 & 26,998 \botline \end{tabular} \vspace*{-6pt} \end{table*} {\vspace*{-2pt}} \subsubsection{Fluorescence quantum yields} The fluorescence spectra in different solvents after excitation at 610~nm are shown in Figure~\ref{fig3}. \begin{figure} \includegraphics{fig03} \caption{\label{fig3}Fluorescence spectrum of \textit{tert}-ZnPc(II) in 10 solvents excited at 610~nm ($7.5\times 10^{-6}~\mathrm{mol}{\cdot}\mathrm{L}^{-1}$).} \vspace*{-1pt} \end{figure} The fluorescence spectra of \textit{tert}-ZnPc(II) reveal two distinct groups of solvents (Figure~\ref{fig3}). In FBS, chloroform, and glycerol, the spectra exhibit two peaks of very low intensity at 690~nm and 725~nm while no fluorescence is observed in water. Conversely, in the remaining solvents, the emission spectra show the characteristic patterns of Pc macrocycles. The first maxima spectra are situated between 680~nm and 690~nm and the second between 740~nm and 750~nm, with both peaks exhibiting higher intensity in alignment with the absorption spectra of Pcs. The fluorescence quantum yields in toluene, ethyl acetate, ethanol, methanol, DMF, and acetonitrile exhibit close values, ranging from 0.35 to 0.27 (Table~\ref{tab2}). In contrast, chloroform, glycerol, and FBS show fluorescence quantum yields less than 0.1 while as expected, the fluorescence quantum yield is zero for water. Notably, the fluorescence quantum yields at 350~nm closely mirror those at 610~nm, indicating that the quantum yield remains consistent \mbox{irrespective} of the wavelength at which it is measured. This emphasizes the wavelength-independent nature of fluorescence quantum yield. \begin{table*} \caption{\label{tab2}Emission band, fluorescence quantum yield of \textit{tert}-ZnPc(II) in different solvents\vspace*{-2pt}} \begin{tabular}{cccccc} \thead Solvents & ${\rmLambda}_{\mathrm{ext}}$ (nm) & ${\rmLambda}_{\mathrm{em}}$ Band 1 (nm) & ${\rmLambda}_{\mathrm{em}}$ Band 2 (nm) & ${\rmLambda}_{\mathrm{em}}$ Band 3 (nm) & $\rmPhi_f$ 610\\ \endthead Toluene & 610 & 689 & 749 & - & 0.35 \\ Ethyl acetate & 610 & 683 & 743 & - & 0.31 \\ Ethanol & 610 & 687 & 746 & - & 0.29 \\ Methanol & 610 & 686 & 745 & - & 0.27 \\ DMF & 610 & 689 & 746 & - & 0.29 \\ Acetonitrile & 610 & 687 & 741 & - & 0.28 \\ Chloroform & 610 & 687 & - & - & 0.03 \\ Glycerol & 610 & 692 & - & - & 0.02 \\ Water & 610 & 700 & 720 & 738 & 0 \\ FBS & 610 & 686 & - & - & ${<}$0.1 \botline \end{tabular} \vspace*{-2pt} \end{table*} \subsection{Effect of pH medium} The UV--vis spectrum of \textit{tert}-ZnPc(II) in water reveals a broader absorption profile with split peaks, exhibiting an extensive broadening of the Q band (Figure~\ref{fig4}). This is accompanied by a red shift in the absorption maximum, compared to toluene, and a blue shift in the Soret band from 350~nm to 336~nm (Table~\ref{tab3}), indicative of H-aggregate formation. The H-aggregate, characterized by a face-to-face arrangement, features a large contact area and strong ${\uppi}\ndash {\uppi}$ forces. Previous research has shown that nonaxial modified phthalocyanines, such as tetra(4-\textit{tert}-butyl)phthalocyanine (abbreviated as TbPc), tend to form H-aggregates during self-assembly~\cite{15}. \begin{figure} \includegraphics{fig04} \caption{\label{fig4}UV--vis absorption spectra of \textit{tert}-ZnPc(II) in water at different pH ($7.5 \times 10^{-6}~\mathrm{mol}{\cdot} \mathrm{L}^{-1}$).} \end{figure} \begin{table} \caption{\label{tab3}Absorbance B and Q bands of \textit{tert}-ZnPc(II) in water at different pH ($7.5\times 10^{-6}~\mathrm{mol}{\cdot}\mathrm{L}^{-1}$) \vspace*{-2pt}} \tabcolsep=2.5pt \begin{tabular}{cccc} \thead Water & B band (nm) & Q band 1 (nm) & Q band 2 (nm) \\ \endthead pH4 & 336 & 630 & 677 \\ pH7 & 337 & 630 & 677 \\ pH10 & 337 & 630 & 677 \botline \end{tabular} \vspace*{-2pt} \end{table} Moreover, pH is identified as a factor that could influence photophysical properties. UV--vis absorption and fluorescence emission of \textit{tert}-ZnPc(II) in water at a concentration of $7.5\times 10^{-6}~\mathrm{mol}{\cdot}\mathrm{L}^{-1}$ were measured under different pH conditions (pH 4, 7, and 10). The absorption spectra are relatively similar for pH 7 and 10, whereas a significant decrease in intensity is observed for pH 4. In water, $7.5\times 10^{-6}~\mathrm{mol}{\cdot}\mathrm{L}^{-1}$ exhibits no fluorescence across all pH ranges, indicating the presence of aggregation (Figure~\ref{fig5}). \begin{figure} \includegraphics{fig05} \caption{\label{fig5}Fluorescence spectrum of \textit{tert}-ZnPc(II) in water excited at 610~nm ($7.5\times 10^{-6}~\mathrm{mol}{\cdot}\mathrm{L}^{-1}$) at different pH.} \end{figure} \subsection{Effect of water concentration on UV--vis absorption properties of \textit{tert}-ZnPc(II)} The observation of a notable change in the Q band shape within the UV--vis absorption spectrum of \textit{tert}-ZnPc(II) in a water environment motivated us to examine the impact of water on the absorption intensity for detecting trace amounts of water in diverse organic solvents, including ethanol, methanol, and acetonitrile. Indeed, water stands as an important and indispensable substance, holding significance not only in the realm of everyday human existence but also within the domain of chemistry. It serves as a \mbox{critical} impurity requiring elimination from numerous chemical and industrial production processes. Water possesses distinctive characteristics that engender specific interactions with excited molecules owing to its substantial dielectric constant and ability to donate and accept protons. This makes it a potential sensor for detecting moisture in organic solvents. Another important factor that needs to be considered is the strong tendency of \textit{tert}-ZnPc(II) to form aggregates. The probe solution of \textit{tert}-ZnPc(II) ($7.5\times 10^{-6}~\mathrm{mol}{\cdot}\mathrm{L}^{-1}$) is dissolved in each of the dry organic solvents ethanol, methanol, and acetonitrile, and various concentrations of water (0--70\%, v/v) were added. All spectra were obtained immediately after the addition of water to each solvent at 25~\textdegree C. Various concentrations of water in ethanol, methanol, and acetonitrile solutions containing \textit{tert}-ZnPc(II) did not lead to significant wavelength shifts or notable changes in spectral shape; the only difference lay in the absorption coefficient magnitudes. Dicelio and colleagues conducted a study on the aggregation of tetra, \textit{tert}-butyl phthalocyanine, revealing that both the monomer and dimer of tetra, \textit{tert}-butyl phthalocyanine exhibited nearly identical UV--vis absorption spectra~\cite{56}. Consequently, the addition of water to \textit{tert}-ZnPc(II) induced the formation of \textit{tert}-ZnPc(II) aggregates without entirely altering the UV--vis absorption spectra. Explaining the shapes and intensities of the dimer spectra accurately would necessitate a comprehensive theoretical investigation, extending Kasha's exciton theory to degenerate excited states and incorporating vibronic coupling into the model as proposed by previous research~\cite{47,57}. The UV--vis absorption spectra of \textit{tert}-ZnPc(II) in ethanol, methanol, and acetonitrile (Figures~\ref{fig6}--\ref{fig8}) exhibited a nearly identical absorption shape even after the addition of varying concentrations of water. However, the notable alteration was observed in the absorption intensity. Specifically, the introduction of small aliquots of water (0.1\%) into ethanol, methanol, and acetonitrile resulted in a decrease in absorption intensity from 1.228 to 0.593, 1.115 to 0.415, and 1.270 to 0.632, respectively. These values were 2, 2.60, and 2 times lower than those observed in pure ethanol, methanol, and acetonitrile, respectively (Tables~4--6 in Supplementary Material). \begin{figure} \includegraphics{fig06} \caption{\label{fig6}UV--vis absorption spectra as a function of water content of \textit{tert}-ZnPc(II) in ethanol at $7.5\times 10^{-6}~\mathrm{mol}{\cdot}\mathrm{L}^{-1}$.} \vspace*{-2pt} \end{figure} \begin{figure} \includegraphics{fig07} \caption{\label{fig7}UV--vis absorption spectra as a function of water content of \textit{tert}-ZnPc(II) in methanol at $7.5\times 10^{-6}~\mathrm{mol}{\cdot}\mathrm{L}^{-1}$.} \end{figure} \begin{figure} \includegraphics{fig08} \caption{\label{fig8}UV--vis absorption spectra as a function of water content of \textit{tert}-ZnPc(II) in acetonitrile at $7.5\times 10^{-6}~\mathrm{mol}{\cdot}\mathrm{L}^{-1}$.} \end{figure} This diminished intensity, attributed to the addition of a minimal quantity of water, emphasizes the high sensitivity of \textit{tert}-ZnPc(II) to water content. The absorption intensity at 674~nm, 673~nm, and 672~nm in ethanol, methanol, and acetonitrile progressively decreased with increasing water \mbox{content} from 0.1\% to (30\%, 10\%, and 70\%), reaching a plateau at each respective concentration. At the 30\%, 10\%, and 70\% water content levels, the absorption intensity at 674~nm, 673~nm, and 672~nm were approximately 7-, 4.62-, and 12-fold lower than in pure ethanol, methanol, and acetonitrile, respectively (Figures~\ref{fig6}--\ref{fig8}). Evidently, a linear decrease in absorption intensity was observed across all wavelengths with increasing percentage of water\unskip\break content. It is noteworthy that despite the likely occurrence of aggregation, the spectra maintained their consistent absorption shapes even when incorporating 30\%, 10\%, and 70\% water into homogeneous solvents of ethanol, methanol, and acetonitrile, respectively. \section{Conclusion} This study focuses on the exploration of \textit{tert}-ZnPc(II) photophysical properties. The investigation highlights the influence of solvent polarity on ground-state electronic absorption spectra and fluorescence capability. It is noteworthy that \textit{tert}-ZnPc(II) exhibits typical UV--vis spectra in all organic solvents examined except chloroform, water, glycerol, and FBS. In these specific solvents, a significant alteration in the shape of absorption spectra is observed coupled with a notable absence of fluorescence, likely attributed to well-known aggregation phenomena inherent in phthalocyanines. Additionally, the UV--vis spectra of \textit{tert}-ZnPc(II) in water demonstrate high sensitivity to water content, maintaining consistent absorption shapes even with the incorporation of a substantial amount of water into the solvents. \section{Materials and methods} All solvents and reagents were of reagent grade quality and obtained commercially from Aldrich, TCI, Fluka, and Merck. \subsection{Photophysical properties} Absorption spectra were recorded on a UV-3600 UV--visible double beam spectrophotometer (Shimadzu, Marne la Vall\'{e}e, France). Fluorescence spectra were recorded on a Fluorolog FL3-222 spectrofluorometer (HORIBA Jobin Yvon, Longjumeau, France) equipped with a 450~W xenon lamp, a thermostated cell compartment (25~\textdegree C), a UV--visible photomultiplier R928 (HAMAMATSU, Japan), and an InGaAs infrared detector (DSS-16A020L, Electro-Optical Systems Inc, PA, USA). The excitation beam and the emission beam were diffracted by a double-ruled grating SPEX monochromator with 1200 grooves/mm blazed at 330~nm and 1200 grooves/mm blazed at 500~nm, respectively. All spectra were measured in four-face quartz cuvettes. All the emission spectra have been displayed with the same absorbance (less than 0.2) with the lamp and photomultiplier correction. \subsection{Parameters for fluorescence quantum yields} The fluorescence quantum yields of \textit{tert}-ZnPc(II) ($\Phi_{f}$) were calculated in different solvents by Equation~(\ref{eq1})~\cite{58}: {\begin{eqnarray}\label{eq1} \Phi_f = \Phi_{f_o} \cdot \frac{I_f}{I_{f_o}} \cdot \frac{DO_o}{DO} \cdot \left(\frac{n}{n_o}\right)^2, \end{eqnarray}}\unskip where ${\Phi}_{f}$ and $\Phi_{f_o}$, $I_{f}$ and $I_{f_o}$, $DO$ and $DO_{o}$, and $n$ and $n_{o}$ are the quantum yields, fluorescence intensities, optical densities, and refractive indices respectively of the sample and the standard. \section*{Funding} The authors thank the French Institute of Tunisia for providing financial support. \section*{Declaration of interests} 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. \section*{Supplementary data} Supporting information for this article is available on the journal's website under \printDOI\ or from the author. \CDRsupplementaryTwotypes{supplementary-material}{\cdrattach{crchim-364-suppl.pdf}} \back{} \bibliographystyle{crchim} \bibliography{crchim20240466} \refinput{crchim20240466-reference.tex} \end{document}