Temperature and solvent effects on rotamer-specific photobehaviour of the cis and trans isomers of 2-styrylanthracene

The photochemical and photophysical behaviour of the two stereoisomers of 2-styrylanthracene (2-StAn) has been investigated as a function of temperature and solvent polarity. The photobehaviour of both the trans and cis isomers markedly depends on the 1Lb or 1(La–Bu) nature of the two lowest singlet excited states and on their energy gap. Furthermore, the deactivation channels of the excited states are markedly dependent on conformer geometry, which produces rotamer-specific photoreactive pathways. The excited state properties were investigated by stationary and pulsed fluorimetric techniques and by laser flash photolysis. This paper reports the photophysical and photochemical parameters of the different conformational geometries (rotamers) of trans-2-StAn and cis-2-StAn. The role played by an upper excited singlet state (S2) of the long-lived B rotamer of trans-2-StAn on the relaxation properties (radiative and reactive) of its S1 state is also discussed. The new and relevant experimental and calculation results, reported in this paper, allow a complete and revised picture of the conformational equilibria and the radiative and radiationless relaxation rate parameters of the two geometrical isomers of 2-StAn to be obtained.