CALCULATION OF THE FORSTER ORIENTATION FACTOR FOR DONOR-ACCEPTOR SYSTEMS WITH ONE CHROMOPHORE OF THREEFOLD OR HIGHER SYMMETRY - ZINC PORPHYRIN

Three different methods of calculation of the Forster orientation fact or, K-2, for donor-acceptor systems in which one of the two chromophor es have threefold or higher symmetry are discussed. Jablonski's symmet rical planar oscillator, as well as two perpendicular linear oscillato rs have been used as models for the transition dipole moment in the hi ghly symmetrical chromophore. The methods of calculation are applied t o zinc porphyrin-free base porphyrin donor-acceptor systems. The best agreement between experimental energy transfer rates or efficiencies a nd those calculated according to Forster theory is achieved when K, no t K-2, is calculated as an average and then squared. The average is ta ken either of an infinite number of K-values or of two K-values, depen ding on the oscillator model used for the transition dipole moment in the zinc porphyrin.