Anisotropy of Absorption and Photoluminescence Spectra of Stretched Poly(3-alkylthiophene)

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Abstract
The remarkable anisotropy of absorption and photoluminescence spectra has been observed in stretched poly(3-alkylthiophene). Upon stretching at room temperature, the absorption spectral peak shifts to a higher energy and the photoluminescence is enhanced. The absorption spectral shape depends on the polarization of light relative to the stretching direction. The luminescence intensity polarized parallel to the stretching direction is enhanced upon stretching but that of perpendicular polarization is suppressed. That is, intrachain excitation and intrachain recombination are mainly responsible for photoluminescence. The excitation spectrum is also found to be dependent on the observed wavelength of luminescence. These results can be explained in terms of the formation of new twisted bonds between neighboring thiophene rings and the confinement of excited species in the narrow excited region on the main polymer chains.