TRANS-]CIS PHOTOISOMERIZATION OF 1-(9-ANTHRYL)-2-(4-R-PHENYL)ETHYLENE, R-CH3 AND OCH3

The quantum yields of fluorescence, triplet formation and trans-->cis photoisomerization (PHI(f) PHI(T) and PHI(t-->c)) of the title compounds (H3C- and H3CO-StA) were measured in several solvents at room temperature. The respective values in acetonitrile are PHI(f) = 0.20 and 0.03, PHI(T) = 0.18 and 0.02, PHI(t-->c) = 0.12 and 0.28. A decrease in the polarity of the solvent results in a strong reduction of PHI(t-->c) for H3C-StA, whereas the other PHI values change only slightly. For H3CO-StA PHI(t-->c) = 0.10 in toluene but is virtually zero in cyclohexane or methylcyclohexane. A singlet mechanism is suggested for trans-cis photoisomerization of the two 9-StA derivatives. Intramolecular charge transfer is indicated for either electron donating or accepting groups (R) of R-StAs.