Silylenes electronic spectra

FIGURE 1. Mesityl(neopentyl)silylene and its dimerization ------denotes electronic spectrum of... 

The fluorescence of the phenyl polymer is similar in shape to the fluorescence from the alkyl polymers and the similar shape of the phosphorescence spectrum, as well, suggests that the origins of the electronic spectrum are also much the same. The apparent increased quantum yield for phosphorescence in poly(phenyl methyl silylene) probably reflects a mixing of the ring electronic levels with the levels of the chain. Both the fluorescence and phosphorescence of the naphthyl derivative are substantially altered relative to the phenyl polymer. Fluorescence resembles that of poly(B Vinyl naphthalene) (17,29) which is attributed to excimer emission. Phosphorescence is similar to naphthalene itself. These observations suggest that the replacement of an alkyl with phenyl moiety does not change the basic nature of the electronic state but may incorporate some ir character. Upon a naphthyl substitution both the fluorescence and phosphorescence become primarily tt-tt like. 

The success of the GIAO calculations in predicting correctly the NMR spectrum of 4a and 5a suggests that this method can be used to study also the NMR spectra of transient silylenes which cannot yet be studied experimentally. Such studies can provide important ftmdamental information on the electronic structure of silylenes. 

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