Intermolecular charge transfer in Langmuir-Blodgett films: Formation of mixed and alternate-layer LB films of quinhydrone and TTF-TCNQ derivatives

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.