Temperature Dependence of Photoinduced Electron Transfer within Self-Assembled Uroporphyrin−Cytochrome c Complexes

Abstract

In this report the temperature dependence of photoinduced electron transfer between both singlet- and triplet-state uroporphyrin (1URO and 3URO, respectively) and the heme group of ferricytochrome c (Cc) has been examined. Analysis of the forward electron-transfer rate originating from 1URO as a function of temperature gives a reorganizational energy (λ) of 1.0 ± 0.02 eV with an associated electronic coupling term (HAB) of (3.7 ± 0.3) × 10-4 eV. In addition, the singlet lifetime data exhibit a temperature-dependent Gaussian distribution that narrows as the temperature increases. This suggests a conformational distribution of bound porphyrin with a narrow range of potential wells at lower temperatures. The corresponding temperature dependence of the electron transfer between 3URO/URO+ and the heme group of Cc gives a λ = 0.49 ± 0.05 eV/0.19 ± 0.03 eV and HAB ∼ 4 × 10-4 eV/1.4 × 10-4 eV, respectively. These observations are consistent with orientational dependent conformational states as well as possible ga...