Vibrational Spectroscopic Features of a Novel Family of Amorphous Molecular Materials Containing an Oligothiophene Moiety as Color-Tunable Emitting Materials

Abstract

In this paper, we investigate the vibrational properties of a novel family of amorphous molecular materials containing an end-capped oligothiophene backbone of variable length, α,α‘-bis-{4-[bis(4-methylphenyl)amino]phenyl}-oligothiophene, which function as color-tunable emitting materials for organic light-emitting diodes. The advantage of these amorphous oligothiophenes with respect to their crystalline parents is that the fluorescence quantum efficiencies as thin films are quite similar to those commonly found in solution. The thorough analysis of the infrared and Raman spectra of the neutral materials as solids has revealed the uselfulness and selectivity of Raman spectroscopy to determine the efficiency of the π conjugation. Density functional theory B3LYP/3-21G* calculations rendered largely distorted conformations of the 4-[bis(4-methylphenyl)amino]phenyl groups with respect to the thiophene rings least-squares plane, in full accordance with the amorphous nature of the materials. The infrared and Raman spectra of the materials recorded at different temperatures between −170 and +160 °C did not show any substantial change, thus indicating that the materials have a high thermal stability, which has significance for their use as active components in optoelectronic devices.