DONOR-ACCEPTOR ENERGY-TRANSFER IN CHOLEIC ACID CRYSTALS

Direct donor-acceptor triplet excitation energy transfer is characterized in 4,4'-dibromobenzophenone/1,4-dibromonaphthalene choleic acid crystals by monitoring the phosphorescence spectra as a function of acceptor concentration. The energy-transfer efficiency does not show an abrupt change unlike the case for a polystyrene host. This difference reveals that the energy-transfer rate is significantly slower in the choleic acid system and is attributed to the intrinsically larger intermolecular distances imposed by the choleic acid lattice. The results indicate that 4,4'-dibromobenzophenone, 1,4-dibromonaphthalene, and deoxycholic acid form a single-phase structure even when mixed nonstoichiometrically and that no composition-related structural phase transition occurs.