Free energy and entropy changes in vertical and nonvertical triplet energy transfer processes between rigid and nonrigid molecules. A laser photolysis study

Article abstract of DOI:10.1021/ja00062a036

The free energy and entropy changes associated with intermolecular triplet energy transfer (TT) processes were determined by direct measurement of the equilibrium constant using a laser flash photolysis technique. 10,10-Dimethylanthrone and 9,9-dimethylfluorene were synthesized and used as a "rigid" donor and acceptor, respectively, in comparison with 4-methylbenzophenone, a "nonrigid" donor, and 4-methylbiphenyl, a "nonrigid" acceptor, in the TT reactions. Both the nonrigid donor and the nonrigid acceptor lose entropy while going from the twisted ground state to the planar triplet state. The ΔS values for 4-methylbenzophenone and 4-methylbiphenyl are 0.5-1.0 and 2.5-3.0 gibbs/mol, respectively.