Fluorescence polarization and dichroic spectra of stilbene derivatives

Fluorescence polarization spectra were measured by means of the single photon counting technique with the use of a setup comprising two quartz monochromators. The relative experiment error did not exceed 3% for polarizations close to the limiting value of 6% for p approx. 0.1. Dichroic spectra of stilbene derivatives were measured with a Specord UV-VIS spectrophotometer. The polarization of the fluorescence emission band for the oxazole derivatives of stilbene is practically constant exhibiting slight increases in the vibration maxima. This polarization behavior indicates that the emission is due to a single electronic transition. The absorption spectra of the oxazole derivatives of stilbene contain three broad bands in the near-UV region. The long-wavelength absorption band (A band) is due to the excitation of the entire ..pi..-electron system of the molecule. Phenyl and oxazole rings lead to the appearance of a new absorption band (R band) with the maximum near 290 nm. The short-wavelength B band is due to the ..pi..-excitation of the benzene rings.