Photophysical behaviour of some pyrenylethylene derivatives and its implication on trans → cis photoisomerisation reactions

The fluorescence properties of some pyrenylethylene derivatives capable of exhibiting twisted intramolecular charge transfer phenomenon havebeen studied as a function of solvent polarity. The solvent polarity dependent change in the fluorescence quantum yield has been interpreted in terms of intramolecular retational relaxations. The trans → cis photoisomerization data of the compounds indicate that the twist around the ethylenic double bond is accelerated in polar solvents.