Conformational Equilibria in Trans 1,2‐Diarylethylenes Manifested In Their Emission Spectra. Part III. (1a). Pyridyl and quinolyl derivatives

Abstract

AbstractThe emission spectra of four 1,2‐diarylethylenes, in which at least one aryl is 3‐pyridyl or 7 or 8‐quinolyl, vary with the wavelength of excitation, indicating the existence of two or three species of each compound with slightly‐shifted emission (and absorption) peaks, in analogy to our earlier reports (1). At temperatures below ‐70°C in solutions in aliphatic hydrocarbons the normal fluorescence is gradually replaced by a broad and almost structureless emission band in the range 400‐550 nm. The conversion takes time, it is virtually complete at ‐120°C. No similar phenomena were observed in toluene/methylcyclohexane mixtures. The results at temperatures above ‐70°C are ascribed to the existence of an equilibrium mixture of rotamers, while those below ‐70°C are suggested to reflect association phenomena.