FOURIER-TRANSFORM INFRARED-SPECTROSCOPY STUDY OF THIN LANGMUIR-BLODGETT-FILMS OF 2-OCTADECYL-7,7,8,8-TETRACYANOQUINODIMETHANE

Fourier transform infrared (FT-IR) transmission and reflection-absorption (RA) spectra have been measured for Langmuir-Blodgett (LB) films of 2-octadecyl-7,7,8,8-tetracyanoquinodimethane (octadecyl TCNQ) deposited on CaF2 (for transmission measurements) and Au (for RA measurements) substrates with various monolayers. Splitting of the CH2 scissoring band near 1465 cm-1 suggests that the hydrocarbon chains of octadecyl TCNQ in the LB films are in an orthorhombic subcell packing. Polarized infrared transmission measurements of the LB films indicate an uniaxial orientation of the hydrocarbon chains with respect to the surface normal. A comparison of the infrared transmission and RA spectra reveals that the hydrocarbon chains are inclined to some extent with respect to the surface normal. As for the TCNQ part, the infrared transmission and RA measurements suggest that the TCNQ plate in the LB films thicker than two monolayers is oriented nearly perpendicular to the surface while its molecular axis, which is defined as shown in Figure 1, is inclined considerably with respect to the surface normal. Examination of the RA spectra of "head-on" and "tail-on" type one-monolayer films indicates that the TCNQ plate in the "head-on" type one-monolayer film is tilted to a certain degree due to the interaction between the TCNQ part and Au substrate.