The photo and thermal cis/trans isomerization reactions are studied for 1-methyl-4-(4ʹ-aminostyryl)pyridinium iodide, Cy, which is prepared in the trans form. In a basic solution the trans form, Cytr, cannot isomerise directly to the cis form. Its protonated form, CytrH+, is active and reacts photochemically from trans to cis configuration, CycH+. The quantum yields Фtc and Фct are determined in water. Deprotonation process of CycH+ yields the cis isomer, Cyc, which can thermally back to the stable trans form. The rate constants and the activated parameters of the thermal reaction are determined. Due to irreversibility of the thermal reaction, a complete molecular reaction cycle is performed in one direction. To get more information on the spectral characteristics of protonated form, the photochromic of the title compound is studied in different fourteen solvents. The linear relationships between absorption energy with hydrogen bond acceptor ability of the solvents and fluorescence energy of CyH+ with free energy for transferring the proton to the solvent, DGto were determined.
Styryl pyridinium cyanine dye, Photochemical and thermal trans/cis isomerization, Photochromism