Hypercoordinate silicon and phosphorus acetylene compounds:: crystal structure determinations and fluorescence spectroscopic study

The steady-state fluorescence, fluorescence excitation spectra and fluorescence lifetime of pentacoordinate [8-(dimethylaminoic-kappaN)-1-naphthalenyl-kappaC]diethynylmethylsilicon as a function of excitation and emission wavelengths were investigated in solvents of various polarities at room temperature. Inhomogeneous spectral broadening and biexponential decay-times (tau(1) similar to 1 ns and tau(2) similar to 15 ns) were associated with the existence of two types of electronic states created as a result of the interaction of the amino group with the pi-conjugated system and the CH3Si(C drop CH)(2) group. The crystal structure of the silicon monomer shows a monocapped tetrahedral geometry in which the N atom is opposite one of the acetylene groups. An interaction between the N and Si atoms is evident, the N-Si distance being less than the sum of the van der Waals radii of the 2 atoms. The crystal structure of the analogous hypercoordinate acetylene phosphorus compound [8-(dimethylamino-kappaN)-1-naphthalenyl-kappaC]diphenylethynylphosphorus is similar, the short P-N distance and only slight distortion of the naphthalene ring reflecting the P-N interaction. Oxidation of the phosphorus compound to the corresponding oxide readily occurs on treatment with hydrogen peroxide. (C) 2004 Elsevier Ltd. All rights reserved.