INFRARED SPECTROSCOPY OF CONJUGATED ORGANIC MOLECULES UNDER HIGH PRESSURE By KIRILL

By Kirill Khamidovich Zhuravlev, Ph.D. Washington State University May 2004 Chair: M. D. McCluskey Conjugated organic molecules are important components in solid-state optoelectronic devices and laser dyes. Changes in the conformations of these molecules affect the optical emission wavelengths. In order to probe the conformation of conjugated molecules, infrared (IR) spectroscopy was performed on organic solids under high hydrostatic pressures. We investigated polyphenyl molecules, such as biphenyl, p-terphenyl, and pquaterphenyl. It was shown that polyphenyl molecules experience a phase transition in which molecules change their conformation from a twisted to a planar structure. This transition manifests itself in dramatic changes in the IR spectra. Beyond a critical pressure, specific IR-active modes abruptly become IR-inactive. IR spectra have been obtained with a Bomem DA8 Fourier-Transform IR spectrometer in the 500-5000 cm spectral range. Those spectra clearly showed that when the pressure increases above the critical value some IR-peaks completely