Photoelectric properties based on photo-induced electron transfer processes in flavin–porphyrin hetero-type Langmuir–Blodgett films

• Published in: Thin solid films Vol. 441; no. 1; pp. 277 - 283
• Main Authors: Isoda, Satoru, Hanazato, Yoshio, Akiyama, Kouichi, Nishikawa, Satoshi, Ueyama, Satoshi
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 22.09.2003; Elsevier Science
• Subjects: Charge separation; Chemistry; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Electron transfer; Electronic structure and electrical properties of surfaces, interfaces, thin films and low-dimensional structures; Electronic transport in interface structures; Exact sciences and technology; General and physical chemistry; Langmuir blodgett films; Metal-insulator-metal structures; Photocurrent; Physics; Surface physical chemistry; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties); Langmuir–Blodgett films; Electron transfer; Photocurrent; Charge separation; MIM devices; Flavin derivatives; Nitrogen heterocycle; Tunnel effect; Polycyclic compound; Aluminium; Photocurrents; Ruthenium complexes; Experimental study; Macrocycle; Thin films; Langmuir-Blodgett films; Metalloporphyrin; IV characteristic; Organic compounds
• ISSN: 0040-6090; 1879-2731
• DOI: 10.1016/S0040-6090(03)00924-6

The photo-induced electron transfer processes were investigated in flavin–porphyrin hetero-type Langmuir–Blodgett (LB) films to clarify the photoelectric properties of metal-insulator-metal (MIM) devices composed of LB films sandwiched within aluminium electrodes. A hetero-type MIM device with a flavin and porphyrin molecular heterojunction (MHJ) showed highly efficient photovoltaic effects and high photoconductivity. In contrast, a homo-type MIM device with flavin and porphyrin LB films exhibited low photovoltaic effects and a short-circuit photocurrent density less than a tenth of that of the MHJ device. Furthermore, the transient photocurrent of the MHJ device showed that the time constant for the charge separation (CS) process in the MHJ device was of a sub-nanosecond order. This was more than two orders of magnitude shorter than the time constant for the CS process in the flavin homo-type MIM device. We concluded that the highly efficient photoelectric properties of the MHJ device were mainly attributable to the fast CS process from the photo-excited flavin to the porphyrin at the MHJ. Considering the long distance between the flavin and porphyrin at the MHJ and the moderate free energy difference, the mechanism underlying the fast CS process might be based on the quantum electron tunneling.