First Polymer System Perylene in Polyethylene

The success of the fluorescence spectroscopy of pentacene in p-terphenyl crystal immediately suggests including pentacene in a different, disordered matrix such as polyethylene. Several attempts in this direction failed, first because of the photoreactivity of pentacene [42] and second because the matrix can greatly influence the photophysical properties of pentacene [66]. As discussed in Section 1.2, the intersystem crossing rate from the excited singlet of pentacene strongly depends on the local site structure. Different environments around pentacene sites in p-terphenyl crystal lead to hundredfold increases of the triplet yield [74]. It is therefore likely that the highly flexible pentacene molecule has an unfavorable triplet yield when included in a polymer. 

In 1991, Basche and Moerner included perylene in polyethylene [71]. The small and rigid perylene molecule has good emission and triplet properties, but absorbs in a difficult spectral region, around 445 nm. Because the spectral jumps we discuss here are mainly consequences of matrix dynamics, we must shortly discuss sample preparation. The samples of [71] were made from low-density polyethylene (crystallinity 25%), doped at low concentration with perylene, and were quickly quenched from the melt to liquid nitrogen temperature to reduce light scattering. The thin films thus obtained were 10 to 20 pm thick. The polymer structure is thus expected to be dominantly amorphous. 

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