Effect of Temperature on the Spectral Fluorescent Properties of Positively Solvatochromic Merocyanines.

Fluorescence quenching of positively solvatochromic merocyanines with a bridge group in the polymethine chain increases linearly with increasing temperature and is enhanced with increased chain length. Analysis of the kinetics of the fluorescence quenching gave the activation energy of this process. The absorption and fluorescence spectra in solvents of different viscosity and polarity at room temperature and 77 K showed that the major channel for fluorescence quenching is photoisomerization of the bonds in the polymethine chain. This conclusion was supported by TDDFT quantum-chemical calculations for the bond lengths of the merocyanines in the ground and excited states. [ABSTRACT FROM AUTHOR]