A re-evaluation of the photophysical properties of 1,4-bis(phenylethynyl)benzene: A model for poly(phenyleneethynylene)

Photophysical measurements, recorded in aerated cyclohexane at 283 K, indicate that 1,4-bis-(phenylethynyl) benzene behaves in a conventional manner, undergoing emission from the lowest vibrational level of the first excited singlet state; there is no evidence for aggregation of this material in cyclohexane solution in the concentration range (1-250) x 10(-6) mol dm(-3). However, in highly viscous, low-temperature glasses, the material does exhibit inhomogeneous fluorescence behavior, and wavelength-dependent excitation and emission spectra, indicative of a slow rate of relaxation of conformers of the excited states compared to the rate of fluorescence.