Aryl polysilylenes

The phosphorescence spectra of the two aryl polysilylenes studied are shown in Figure 9 and their fluorescence at room temperature in Figure 10. Although phosphorescence quantum yields for these two polymers were not measured, estimates based on comparison with the alkyl intensities indicate that these polymers emit with substantially greater yield. Todesco and Kamat (21 ) have measured the phosphorescence yield of a copolymer of a-naphthyl methyl and dimethyl silylene units to be 0.39. Our naphthyl polymer gives clearly the most intense phosphorescence and probably has a quantum yield near the 0.39 value for the copolymer. We estimate the phenyl polymer yield to be = 1/10 of the naphthyl polymer. 

Polysilanes (or polysilylenes) consist of a silicon-catenated backbone with two substituents on each silicon atom (Structure 1). The groups R and R attached to the silicon chain can be of a large variety. Polysilanes with alkyl and/or aryl substituents have been the most thoroughly investigated [1-3], whereas polysilanes having at least a heteroatom substitution such as H, Cl, OR, NR2 have received much less attention [4]. The number of silicon atoms is usually from several hundreds to several thousands. 

Soluble disubstituted polysilylenes are a class of polymers that recently has generated great interest. These polymers have the structure [-SiRR -] , in which R and R may be aryl or alkyl groups and R may be the same as R. The substituted polysilylenes exhibit a wide variety of physical properties, depending on the nature of R and R. Of particular interest is their intense UV absorption at 300-400 nm both in solution and in the solid state, a property conferred by the silicon backbone and accompanied... 

Another class of soluble polysilylenes exhibits essentially no or very weak thermochromism. This class includes poly(cyclohexylmethyl- 15, 38), poly(phenylmethyl- 15, 38), (polytrimethylsilylmethyl- 15), and poly(diarylsilylenes) 46), all of which appear to be conformationally locked over a wide range of temperatures. In terms of our theoretical perspective, this behavior would arise from the steric effects of bulky substituents, which imply a large value of e and, hence, a small coupling constant Vj /e. For aryl-substituted polysilylenes, the proximity of an aromatic group to the backbone could also stabilize a highly ordered rodlike conformation via enhanced dispersion interactions. 

We have studied the thermochromism of fluorescence and show this behavior to be consistent with the rotational isomeric state model previously proposed to explain solution thermochromism in absorption (9,10). Weak, structured phosphorescence is observed from all polymers studied. The contrast between the structured phosphorescence and the narrow fluorescence is interpreted as evidence that the triplet state is the immediate precursor to photochemistry. Finally, the change in the fluorescence character in the aryl series on going from phenyl substitution to naphthyl substitution suggests a change in the nature of the transition from one involving mixed side chain-backbone states in the phenyl case to one which is primarily side chain-like for naphthyl-substituted polysilylenes. 

We have examined the emission spectra of a variety of polysilylenes as thin films and solutions. The solution fluorescence ther-mochromism provides evidence to support the rotational isomeric state model used to interpret the absorption spectrum. The structured character and low yield of phosphorescence in the alkyl polysilylenes suggest that the triplet is the immediate precursor to photochemical scission. The change in character of both fluorescence and phosphorescence on progressing from phenyl to naphthyl in the aryl series indicates that the transitions in the naphthyl polymers are principally ir—it. ... 

Polysilanes (polysilylenes) consist of a linear chain of silicon atoms carrying two substituents, generally, either allqrl or aryl.(l,2,3) Interest in these materials stems from their unique properties, such as sigma-catenation and thermochromic behavior. They have potentid applications as photoresists, electro-optical devices, non-linear optical mateikls, and also as precursors to silicon carbide. 

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