Influence of pH on photophysical properties of (E)-1-(4-chlorobenzyl)-4-(4-hydroxystyryl)pyridinium chloride.

Authors:
Mateusz Gierszewski
Mateusz Gierszewski
A. Mickiewicz University
Jerzy Karolczak
Jerzy Karolczak
Adam Mickiewicz University
Poland
Dr. Igor Khmelinskii, PhD, Prof. Agregado
Dr. Igor Khmelinskii, PhD, Prof. Agregado
University of the Algarve
PhD, Prof. Agregado
physcal chemistry; spectroscopy; climate science
Faro, Algarve | Portugal
Marek Sikorski
Marek Sikorski
A. Mickiewicz University
Poland

Photochem Photobiol Sci 2012 Sep 29;11(9):1454-64. Epub 2012 Jun 29.

Faculty of Chemistry, A. Mickiewicz University, Grunwaldzka 6, 60-780 Poznań, Poland.

The protonation/deprotonation equilibrium was investigated for N-p-chlorobenzyl-substituted (E)-4'-hydroxy stilbazolium halide, namely (E)-1-(4-chlorobenzyl)-4-(4-hydroxystyryl)pyridinium chloride (EPC). Absorption, emission and synchronous scanning spectra were used to explain the observed phenomena. The excited state lifetimes of the protonated and deprotonated forms of EPC were measured and discussed. Absorption spectra were used to determine its pK(a) value in the ground state. We conclude that the protonation/deprotonation equilibrium is not attained in the first excited state of EPC, for kinetic reasons. The quinoid and benzenoid structures of EPC in the ground and excited state are discussed in acidic and basic range of pH. Aqueous solutions of EPC were yellow at pH < 7 and red at pH > 7, and addition of alcohols (methanol or 2-propanol) enhanced this change. Therefore, quaternary stilbazolium salts were investigated for application as acid-base indicators.

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September 2012
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