Intermolecular Charge Transfer in Langmuir-Blodgett Films: Formation of Mixed and Alternate-Layer LB Films of Quinhydrone and TTF-TCNQ Derivatives

Abstract

Intra- and interlayer charge transfer properties were examined in the mixed and the alternate-layer Langmuir-Blodgett (LB) films of 2-methyl-5-octadecyl-1,4-dihydroxybenzene (C18HQ) and 2-methyl-5-octadecyl-1,4-benzoquinone (C18Q), which is an example of the “neutral” charge transfer complex, and 2-hexadecyl-3-heptadecyl-6,7-dimethyltetrathiafulvalene (C16C17DMTTF) and 2-octadecyl-7,7,8,8-tetracyanoquinodimethane (C18TCNQ) for the “ionic” complex. In the former case, intermolecular charge transfer took place in both types of LB films. The charge transfer band between C18HQ and C18Q appeared at 590 nm even for the bilayer film. The charge transferred state should be accompanied by hydrogen bonding, although the IR spectra revealed that a certain amount of non-hydrogen bonded C˭O group exists in the film. The 1:1 mixture of C16C17DMTTF and C18TCNQ gave an ionic charge transfer complex in the form of mixed LB films. UV-visible and IR spectra revealed the strong complex formation during the film-forming process. On the other hand, the charge transfer interaction between the adjacent layer of the interleaved LB films essentially did not take place.