| Abstract: | The polarized excitation and fluorescence spectra of lowcrystalline, isotropic poly(ethylene terephthalate) (PET) film samples were measured in the glassy state at room temperature. Whereas the emission anisotropy r0 of the excitation spectrum, recorded at the fluorescence maximum, changes sharply from 0.35 to 0 with decreasing wavelength in the region around 317 nm, the polarization of the fluorescence spectrum of PET is independent of wavelength. The fluorescence polarization of PET remains constant, if the temperature is increased up to 22 °C above Tg until the light scattering due to the crystallization causes complete depolarization. The photophysical behaviour supports the existence of a dilute solution of groundstate - stable sandwich dimers in the non-crystalline regions of PET. |
