Optical spectroscopy of highly ordered poly(p-phenylene vinylene)

The authors report a study of the photophysical properties of poly(p-phenylene vinylene), PPV, prepared in a way that gives an especially high degree of intrachain order. Optical absorption, photoluminescence, photoinduced absorption, and photoconductivity excitation spectra are presented and compared to data reported for less well ordered PPV. Spectral red shifts, sharpening of spectral lines, and a transfer of oscillator strength into the vibronic ground states of the electronic transitions are observed. Photoinduced absorption due to long-lived charged excitations, previously reported for less ordered PPV, could not be detected in this material. Photoconductivity excitation spectra show a steep rise at the absorption edge with no appreciable offset between the onsets for photoconduction and absorption. A very slow photocurrent component is observed, which the authors associated with the trapping and subsequent thermal release of photocarriers.