Bimanes. 27. Rates of intramolecular singlet-singlet and triplet-triplet energy transfer within one molecule, an anti,syn-bisbimane

Intramolecular singlet-singlet (anti → syn) and triplet-triplet (also anti → syn) energy transfer has been observed in the bisbimane 3, a syn-anti-bisbimane, in which a dimethylene bridge connects the photophysically active moieties. The rate constants for both types of energy transfer have been estimated on the basis of radiative rate constants and quantum yields of fluorescence and phosphorescence of syn-1 and anti-2 bimanes and rate constants of intersystem crossing and photochemical reaction in an anti-bimane. The efficient anti → syn energy transfer may involve exchange augmented by dipole-dipole transfer.