Highly fluorescent solid-state asymmetric spirosilabifluorene derivatives

A series of four asymmetrically aryl-substituted 9,9'-spiro-9-silabifluorene (SSF) derivatives, 2,2'-di-tert-butyl-7,7'-diphenyl-9,9'-spiro-9-silabifluorene (PhSSF), 2,2'-di-tert-butyl-7,7'-dipyridin-2-yl-9,9'-spiro-9-silabifluorene (PySSF), 2,2'-di-tert-butyl-7,7'-dibiphenyl-4-yl-9,9'-spiro-9-silabifluorene (BPhSSF), and 2,2'-di-tert-butyl-7,7'-bis(2',2"-bipyridin-6-yl)-9,9'-spiro-9-silabifluorene (BPySSF) are prepared through the cyclization of the corresponding 2,2'-dilithiobiphenyls with silicon tetrachloride. These novel spiro-linked silacyclopentadienes (siloles) form transparent and stable amorphous films with relatively high glass transition temperatures (T-g = 203-228 degrees C). The absorbance spectrum of each compound shows a significant bathochromic shift relative to that of the corresponding carbon analogue as a result of the effective sigma*-pi* conjugation between the sigma* orbital of the exocyclic Si-C bond and the pi* orbital of the oligoarylene fragment. Solid-state films exhibit intense violet-blue emission (lambda(PL) = 398-415 nm) with high absolute photoluminescence quantum yields (Phi(PL) = 30-55%).