WAVELENGTH-DEPENDENT TRANS TO CIS AND QUANTUM CHAIN ISOMERIZATIONS OF ANTHRYLETHYLENE DERIVATIVES

Anthrylethylene derivatives 1-4 were synthesized to study their photoisomerization. Interestingly 1 and 2 displayed wavelength dependent trans to cis photoisomerization, whose origin is due to preferential light absorption and excitation of the trans isomer. Triplet sensitization studies revealed that these anthrylethylenes undergo only cis to trans isomerization and not trans to cis isomerization. UV-vis absorption, fluorescence emission, and fluorescence quantum yields were determined for all anthrylethylenes. Dual fluorescence is observed for 1, 2, and cis-1, indicating two different emissive states. The fluorescence solvatochromism displayed by 1, 2, and cis-1 is a clear indication of the involvement of a charge transfer excited state. The quantum yield of isomerization was determined in various solvents and also as a function of concentration. We report here the first ''quantum chain isomerization'' that originates from a singlet excited state. The rationale put forward for the observed quantum chain isomerization process is the involvement of adiabatic isomerization from the singlet excited state and subsequent energy transfer to a ground state molecule.