Aggregation-induced reabsorption of p-terphenyl in Langmuir-Blodgett films: a spectral study

Abstract

Mono- and multilayers of nonamphiphilic p-terphenyl (TP) mixed with a fatty acid have been incorporated in Langmuir-Blodgett (LB) films. The surface pressure-area isotherm suggests that the molecules stand almost vertically at the air-water interface. In LB films and in ethanol-water binary mixtures, both ¹L_a and ¹L_b bands appear in absorption spectra, the latter being absent in pure ethanol. The appearence of the ¹L_b band has been attributed to the organization of TP molecules. The higher energy bands of the emission spectra in solution are not manifested in the LB films. This phenomenon has been attributed to reabsorption induced by aggregation. This has been further verified by the emission spectra in ethanol-water mixtures. The role of the ¹L_b band has the reabsobing state in LB films has been supported by exciation spectra. Comparison of the emission and exciation spectra of TP in solution, in LB films, and in ethanol-water mixtures suggests formation of low-dimensional aggregates of TP molecules in LB films. Scanning electron miroscopy also supports the existence of such aggregates in LB films.