The photophysics and electronic spectroscopy of 9,10-bis(phenylethynyl)anthracene (BPEA) were studied using absorption spectroscopy with polarized light, fluorescence anisotropy, and simple semiempirical calculations. The UV-vis spectrum of BPEA in fluid media shows a diminished vibrational resolution as compared to the fluorescence spectrum, whereas this resolution is recovered when a polyethylene film is used as the solvent. By comparison with the results of the semiempirical calculations, we conclude that the behavior in fluid media is a result of the coexistence of several conformations. In contrast, only the planar conformation exists in the polymer, giving a well-resolved spectrum. Dichroic UV-vis spectra show that the lowest energy transition is polarized along the long axis of the molecule (short axis of the anthracene frame) and shows the existence of an overlapping blue-shifted band with perpendicular polarization, which has null oscillator strength in pristine anthracene. The spectral overlap is also evidenced in both the excitation wavelength dependence of the limiting fluorescence anisotropy and the results of the semiempirical calculations.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry