Structural change of Langmuir and Langmuir–Blodgett films of alkylDCNQI induced by charge-transfer reaction at the air–water interface

Abstract

UV-visible absorption spectrum of pure 2-methyl-5-octadecyl-N,N′-dicyanoquinonediimine (C18MeDCNQI) Langmuir films and that of C18MeDCNQI–CuI mixed Langmuir films indicated the occurrence of charge-transfer (CT) reactions at the air–water interface in the latter case. These Langmuir films were deposited onto solid substrates as Langmuir–Blodgett (LB) films by the horizontal lifting method. Polarized UV–visible–IR absorption spectra and x-ray diffraction patterns recorded for the obtained LB films revealed a drastic structural change induced by the CT reactions: An interdigitated bilayer structure was suggested for the pure films, while a monolayer structure for the CT films. Furthermore, the CT degree of the major component of the mixed LB films was estimated at −1, unlike in the case of Cu–DCNQI crystals, for which the CT degree is −2/3.