Thermal Behavior of One-Layer Langmuir-Blodgett Films of 2-Pentadecyl-7,7,8,8-Tetracyanoquinodimethane Studied by Ultraviolet-Visible and Infrared Spectroscopies

Abstract

Thermal Behavior of one-layer Langmuir-Blodgett (LB) films of 2-pentadecyl-7,7,8,8-tetra-cyanoquinodimethane (pentadecyl-TCNQ) has been investigated by use of infrared (IR) and ultraviolet-visible (UV-Vis) spectroscopies. An IR transmission spectrum of the film shows gradual temperature-dependent changes below the melting point of the film, and then gives dramatic spectral changes near the melting point. Temperature-dependent UV-Vis spectral changes of the film indicate that the morphological changes occur in domains of the film, and that absorption bands in the 320–560 nm region arising from the π-π* transition of the chromophore consist of at least three components due to different forms of chromophore aggregation. More active state of the alkyl-chain, hexagonal state, seems to be a trigger for the morphological changes in the domains.