Electronic factor for photoinduced electron transfer in porphyrin–bridge–quinone systems

Quantum-chemical calculations at a semiempirical level (CNDO/S) are used for porphyrin–bridge–quinone systems and at an ab initio and semiempirical level for CH2–bridge–CH22− systems. In both cases the bridge is constituted by a number of aromatic, saturated or mixed units. From these calculations the electronic factor (Δ) is obtained, for photoinduced reaction (PET) in the first case and for thermal reaction in the second case. The relative efficiency of the bridges is discussed. For phenylene and staffane units, a non-exponential dependence of Δ with distance is observed for PET, while for the other two bridges the exponential behavior prevails.