The photophysics and photochemistry of 2-styryl-anthracene and related compounds: extreme variations in triplet—triplet absorption spectra with the temperature, decay anomalies and transcis photoisomerization

Abstract

Transient triplet—triplet absorption spectra and decay curves of 2-styrylanthracene and four related compounds were determined with conventional microsecond flash spectroscopy over a wide range of temperatures between room temperature and −170 °C, in decalin and methyltetrahydrofuran as solvents. The main anomalies observed were as follows: pronounced variation in the triplet absorption spectra with the temperature and, to some extent, with the wavelength of the exciting light; “growing-in”; initial fast decay stages; non-monoexponential decay; variation in the decay rate with the wavelength of measurement. All these were observed at certain temperatures and wavelengths for each compound. Some of these anomalies may be due to the fact that 2-styrylanthracene and its derivatives exist in solution as an equilibrium mixture of two modifications, possibly rotational conformers, both in the ground and in the excited state. Some trans—cis photoisomerization, both direct and sensitized, takes place in all compounds, except possibly in 2-styrylanthracene, and is more pronounced in bromobenzene solutions.