Near-edge X-ray absorption fine structure spectroscopy on ordered films of an amphiphilic derivate of 2,5-diphenyl-1,3,4-oxadiazole

The surfaces of ordered films formed from an amphiphilic derivative of 2,5-diphenyl-1,3,4-oxadiazole by the Langmuir-Blodgett (LB) technique and organic molecular beam deposition (OMBD) were investigated by the use of near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. For the assignment of the spectral features of the C, N, and O K-edge absorption spectra, fingerprint spectra of poly(p-phenylene terephthalamide) (Kevlar), poly(ethylene terephthalate), poly(p-phenylene-1,3,1-oxadiazole), and 2,5-di(pentadecyl)-1,3,4-oxadiazole, which contain related chemical moieties, were recorded. Ab initio molecular orbital calculations, performed with explicit treatment of the core hole, are used to support the spectral interpretations. Angle-resolved NEXAFS spectroscopy at the C, N, and O K-edges suggests a preferentially upright orientation of the oxadiazole derivative in the outermost layer of the films. X-ray specular reflectivity data and molecular modeling results suggest a similar interpretation.