Quantum electron tunneling in flavin–porphyrin hetero-type Langmuir–Blodgett films

Abstract Photo-induced electron transfer in flavin–porphyrin hetero-type Langmuir–Blodgett (LB) films and its temperature dependence were investigated by means of the photocurrent measurements and the transient fluorometry. From 10 K to room temperature, transient photocurrent in sub-nanosecond time region was found to be independent of the temperature for a metal–insulator–metal device composed of the hetero-type LB films with a flavin–porphyrin molecular heterojunction (MHJ). This transient photocurrent was attributed to the charge separation (CS) process from the photo-excited flavin to the porphyryin at the MHJ on the basis of the temperature dependence of the fluorescence decay profiles of the excited flavin. By integrating these results with UV–visible absorption spectra, it was deduced that the fast temperature-independent CS process at the flavin–porphyrin MHJ was mainly due to the quantum electron tunneling regulated by high-frequency quantum modes of intramolecular vibrations.