Spectral and Quantum-Chemical Studies of the Band Shape in Absorption of Merocyanine Derivatives of Cyclohexadienone

A combined study of dyes from the merocyanine series was performed. The chemical constitution of variable donor terminal groups was shown to have an important influence on the electronic structure of merocyanine molecules and their electron transitions. It was established that the long-wavelength band in the visible absorption spectra is inherent to the first electron transition. The resolution of the band into its vibrational components allows pinpointing the position of the 0 -> 0' transition, comparing it with the calculated wavelength of the first electron transition, and performing a correct estimate of the Stokes shift in the fluorescence spectra. Resolved spectra indicate that the position and shape of the absorption band in merocyanines with similar effective donor group lengths are determined by the asymmetry of the chromophore, while spectral properties depend on the competing factors of effective length and basicity.