Structural Characterization of Mixed-Stack Charge Transfer Films of 2-Octadecyl-7,7,8,8-tetracyanoquinodimethane and 5,10-Dimethyl-5,10-dihydrophenazine Prepared by the Langmuir−Blodgett Technique and Donor Doping. 1. Molecular Orientation and Structure Investigated by Ultraviolet−Visible−Near-Infrared and Infrared Spectroscopies and X-ray Diffraction

Abstract

Molecular orientation and structure in mixed-stack charge transfer (CT) films of 2-octadecyl-7,7,8,8-tetracyanoquinodimethane (octadecyl-TCNQ) doped by 5,10-dimethyl-5,10-dihydrophenazine ((Me)2P) have been investigated by using ultraviolet−visible−near-infrared (UV−vis−NIR) and infrared (IR) spectroscopies and X-ray diffraction. The degree of charge transfer (ρ) was determined to be 0.5 by a shift of a b1u C⋮N stretching band of the TCNQ chromophore, suggesting that the complex is close to the neutral−ionic boundary. An X-ray diffraction pattern indicates that the CT films consist of a highly ordered multilayered structure in which donor ((Me)2P) and acceptor (octadecyl-TCNQ) molecules are periodically arranged. The d value was calculated to be 3.3 nm, implying that each layer of the CT films comprises bimolecular layers. Comparison of IR intensities of b1u, b2u, and ag C⋮N stretching bands of the acceptor (A) and a totally symmetric band at 1255 cm-1 of the donor (D) between the transmission and reflectance absorption (RA) IR spectra indicates that the chromophores of D and A are almost perpendicular to the substrate surface with their long molecular axes being nearly parallel to the surface normal in the one-layer mixed-stack CT films. The hydrocarbon chain of octadecyl-TCNQ was evaluated to lie on the substrate. In the multilayer CT films the D and A chromophoric planes seem to be slightly tilted with respect to the substrate surface.