Photoinduced electron transfer in a MIM device composed of ferrocene-flavin-viologen-TCNQ molecular heterojunctions

A molecular photodiode was fabricated with the hetero-type Langmuir-Blodgett (LB) film consisting of two electron accepters (A(1), A(2)). a sensitizer (S) and an electron donor (D). N-Docosylquinolinium TCNQ, N-Allyl-N'-[3-propylamido-N",N"-di(n-octadecyl)]-4,4'-bipyridinium dibromide, 7,8-dimethyl-10-dodecyl isoalloxazine and 1-1'ferrocene-N-dioctadecyl carboxamide were used as A(2), A(1), S and D units, respectively. One-way electron transfer from D to S was observed with cyclic voltammetry for the modified electrode containing complex S/D LB layers. Also, one-way electron transfer in S/A(1), S/A(2) and S/A(1)/A(2) was observed based on the fluorescence quenching measurement in the complex LB layers. By aligning hetero-type LB films of A(2)/A(1)/S/D four units on ITO glass with an aluminum thin film, a molecular photodiode with the metal/insulator/metal (MIM) structure was constructed. Due to excitation by irradiation with a 460 nm monochromatic light source, the photoinduced unidirectional flow of electrons in the MN device could be achieved and was detected as photocurrents. The direction of energy flow was in accordance with the energy level profile across the LB films. The photoswitching function was achieved and the rectifying characteristic was observed in the molecular device. (C) 1998 Elsevier Science S.A. All rights reserved.