TRANSIENT ABSORPTION SPECTROSCOPY OF POLYGERMANE COPOLYMER

University Of Pennsylvania, Philadelphia PA

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Abstract

In an investigation of the electronic properties of a series of copolymers, poly[methylphenyl-co-methyl-4-(dimethylamino)phenylgermane] and the corresponding homopolymers, the copolymers containing 5%, 25%, and 50% dimethylaminophenyl units show a broad emission peak at ~500 nm. This is in addition to contributions from a sharp emission peak at ~375 nm exhibited by the phenyl homopolymer and a broader peak at ~420 nm found in the emission of the dimethylaminophenyl homopolymer. In an investigation of an analogous series of polysilane copolymers, Hochstrasser and Miller observed a broad emission peak at ~420 nm, which they attributed to a "self-trapped exciton", or an excitation which is localized on ~1 dimethylaniline unit. Furthermore, literature reports of the emission spectrum of poly(phenylmethylsilane) indicate the presence of two peaks a sharp peak at ~355nm and a broader peak at ~400-500 nm. The origin of the latter peak is controversial, and has been propose d to be due to phosphorescence, impurities generated during polymerization or during photolysis, or a charge transfer state between the polymer backbone and pendant groups. Our goal is to determine the origin of the broad emission peak which we are observing at ~500 nm. It seems likely that it is due to a "self-trapped" exciton as postulated by Hochstrasser et al. However, it is necessary to rule out the possibility of phosphorescence, and transient absorption spectroscopy is a relatively quick method to detect long lived species which may be responsible for phosphorescence.