Molecular aggregation and photochemical Z/E isomerization of 1-methy-2-[2-(9-phenantheryl)ethenyl] benzothiazolium iodide

The steady state absorption and fluorescence spectra of a hemicyanine dye namely, 1-methy-2-[2-(9-phenantheryl)ethenyl] benzothiazolium iodide (9-PhEBI), were measured in different solvents of various polarity including; H2O, MeOH, EtOH, CH3CN, CH2Cl2 and CHCl3. The photochemical and thermal reactivities were studied in MeOH, EtOH and CH3CN solvents. The molecular aggregation of 9-PhEBI and formation of J-aggregates was observed in the used solvents even at low concentrations. Further aggregation, with changing the color of the dye from pale yellow to violet, was observed in water. Quantum chemical calculations were employed in order to investigate the intramolecular charge transfer (ICT) process and some quantum chemical parameters. A good agreement between the experimental and theoretical results was found.