PHOTOCHEMICAL BEHAVIOR OF 2-[2-(2-PYRIDYL) ETHENYL] INDOLE ON TRIPLETSENSITIZATION - SPIN MULTIPLICITY DEPENDENCE OF THE ISOMERIZATION MODES OF AN INTRAMOLECULARLY HYDROGEN-BONDED COMPOUND

Although 2-[2-(2-pyridyl)ethenyl]indole undergoes one-way E --> Z isom erization in the excited singlet state, it isomerizes between the E an d Z isomers in the excited triplet state. On the basis of the determin ation of the quantum yields of isomerization and the photostationary s tate isomer ratios, as well as transient spectroscopic measurements, t he potential energy surfaces for E-Z isomerization in the triplet stat e have been proposed. Specific rotamers of the E and Z isomers are fou nd to be responsible for the triplet state isomerization reactions.