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    Influence of water on photophysical properties of N-bromobenzyl- or nitrobenzyl derivatives of substituted 4-hydroxystilbazolium hemicyanines.
    Photochem Photobiol Sci 2011 Oct 1;10(10):1670-9. Epub 2011 Aug 1.
    Faculty of Chemistry, Adam Mickiewicz University, Grunwaldzka 6, 60-780, Poznań, Poland.
    Absorption, steady-state and timed-resolved fluorescence spectra of nine N-p-bromobenzyl substituted (E)-4'-hydroxy-4-stilbazolium bromides and N-p-bromo- (or nitro-) benzyl substituted (E)-4'-hydroxy-3'methoxy-4-stilbazolium bromides, belonging to the hemicyanine class of compounds, were studied in dry and water-containing polar solvents and in water. All of the studied compounds displayed negative solvatochromism. In solvents with small amounts of water the solutions of each of the compounds change color to red, blue-green or blue, while in extra dry solvents they are all yellow. The new band causing the change in color is interpreted as belonging to the deprotonated form of the respective compound. The absorption and emission spectra of protonated and deprotonated forms of hemicyanines in solvents are presented in comparison with those of selected, isolated deprotonated forms (merocyanines) of the same compounds. The discrimination between the quinoid and zwitterionic deprotonated forms was achieved based on the absorption band location. Time-resolved fluorescence measurements in selected dry and water-containing solvents were also performed.

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    Laboratory of Applied Photochemistry, Faculty of Chemistry, A. Mickiewicz University, Grunwaldzka 6, 60-780 Poznań, Poland.
    Absorption and steady-state fluorescence spectra of nine N-p-(m- and o-) chlorobenzyl substituted (E)-2'-(3' and 4')-hydroxy-4-stilbazolium chlorides belonging to the hemicyanine class of compounds were studied in extra dry alcohols of different polarity. Derivatives with 2'-hydroxy or 4'-hydroxy substituent in the benzene moiety of stilbazol molecule displayed negative solvatochromizm. On the other hand, the excited state decay of compounds with a 3'-hydroxy group in the benzene moiety was dominated by non-radiative processes in protic solvents. Read More
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    Faculty of Chemistry, A. Mickiewicz University, Grunwaldzka 6, 60-780 Poznań, Poland.
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    Photochem Photobiol 1993 Apr;57(4):616-28
    Department of Chemistry, University of Illinois, Urbana 61801.
    A tetrahydrochrysene system that embodies a hydroxy- and nitro-substituted stilbene chromophore held rigidly near planarity by the tetracyclic nature of the compound was prepared as a fluorescent ligand for the estrogen receptor. It shows strong solvent-dependent fluorescence at long wavelengths. The solvent polarity dependence suggests that the fluorescence arises from an excited state with much n pi * character in cyclohexane; stronger emission comes from an intramolecular charge transfer state that has lower energy in more polar solvents, and finally progressive quenching of the charge transfer state occurs in solvents of higher polarity. Read More
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    Departamento de Quimica Inorganica, Instituto de Ciencia de Materiales de Aragon, Facultad de Ciencias, Universidad de ZaragozaCSIC, Plaza S. Francisco s/n 50009 Zaragoza, Spain.
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