Electrochemical and photophysical properties of a series of group-14 metalloles

A series of six group-14 dimethyl- or diphenyl-tetraphenylmetallacyclopenta dienes were synthesized and characterized by their spectroscopic and electr ochemical properties. The group-14 elements investigated were silicon, germ anium, and tin. (The compounds are designated according to the heteroatom a nd the substituent on the heteroatom, i.e., SiMe, SiPh, ..., SnPh.) Five of the six compounds luminesce in both the solid state and in solution. The e mission maxima of SiPh, GePh, and SnPh are invariant to a change in the het eroatom, while for SiMe, GeMe, and SnMe there is a strong dependence of the emission maxima on the identity of the heteroatom. SiMe emits at a longer wavelength than GeMe, while SnMe is not luminescent. The dramatic luminesce nce difference between the two tin compounds was investigated. C-13 NMR cou pling to Sn-119/117, observed in both SnMe and SnPh, was used to make C-13 NMR resonance assignments. Qualitative results of semiempirical molecular o rbital calculations support the C-13 NMR assignments. The crystal structure data for SnPh was obtained at 20 degrees C: a = 10.353(2) Angstrom, b = 16 .679(2) Angstrom, c = 9.482(1) Angstrom, alpha = 99.91(1)degrees, beta = 10 6.33(1)degrees, gamma = 77.80(1)degrees with Z = 2 in space group <P-(1)ove r bar>. It is proposed that the increased electron density at tin in SnMe i s responsible for the deactivation of the emissive state. The presence of p henyl substituents in SnPh serves to stabilize the emissive state and lumin escence is observed.