Photoinduced electron transport processes in hetero-Langmuir-Blodgett (LB) films composed of electron sensitizer (S), relay (R) and acceptor (A) molecules were investigated by femtosecond transient absorption technique. 7,8-Dimethyl-10-dodecyl isoalloxazine (flavin), N-allyl-N′-3-propylamido-N″, ″-di(n-octadecyl)-4,4′-bi pyridium dibromide (viologen) and N-docosilquinolinium tetracyanoquinodimethane (TCNQ) were employed as S, R and A units, respectively. Based on the time-resolved transient absorption spectra of S/R/A series hetero-LB films with different numbers of R layers, the optimum number of R layers for efficient photoinduced charge transport from S to A layers via R was determined to be two. Over two layers of R molecules in the S/R/A series LB films, the charge transport rate became slower due to an increase in the back electron transport from R to A layers. S(30 layers)/A(31 layers) (S(30)/A(31)) hetero-LB film exhibits nearly the same charge transport rate as S(30)/R(2)/A(31) hetero-LB film. But the charge recombination from A to S occurred in S(30)/A(31) hetero-LB film. In the S(30)/A(31) hetero-LB film, charge separated species were directly monitored in the transient absorption spectra. At 660 nm, a long decay component become manifest due to the contribution of bulk (TCNQ)2- species. At 740 and 840 nm, on the other hand, a slow rise and long-time decay components were observed due to the contribution of TCNQ- monomer existing at the interface between S and A layers.
Bibliographical noteFunding Information:
This work has been financially supported by the National Creative Research Initiatives of the Ministry of Science & Technology and supported by grants from the Ministry of Science & Technology (M1-0027-00-0009).
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics
- Mechanics of Materials
- Mechanical Engineering
- Metals and Alloys
- Materials Chemistry