Inorganic-cored photoactive assemblies: synthesis, structure, and photochemical investigations on stannoxane-supported multifluorene compounds

Organostannoxanes were used as inert supports for the preparation of multichromophore assemblies. The synthesis involves a single-step procedure and allows the preparation of compounds in which the number of chromophore units can be varied from one to six. Thus, the reactions of LCOOH (1-fluorenecarboxylic acid) or L'COOH (9-fluorenecarboxylic acid) with various organostannoxane precursors afforded the fluorenyl derivatives Ph(3)SnO(2)CL] (1), Ph(3)SnO(2)CL'] (2), {nBu(3)SnO(2)CL'}(n)] (3), {nBu(3)SnO(2)CL'}(n)] (4), {tBu(2)Sn(OH)O(2)CL}(2)] (5), {tBu(2)Sn(OH)O(2)CL'}(2)] (6), {nBu(2)SnO(2)CL](2)O}(2)] (7) {nBu(2)SnO(2)CL'](2)O}(2)] (8), {nBuSn(O)O(2)CL}(6)] (9), and {nBuSn(O)O(2)CL'}(6)] (10). Interestingly, the formation of 3 is accompanied by an unusual oxo-transfer reaction. The ligand L is oxidized at the 9-position. Compounds 1, 3, 5, 7, and 8 were characterized by X-ray crystallography. The solid-state structures of these compounds reveal rich supramolecular structures owing to multiple intermolecular interactions between the various supramolecular synthons present in these molecules. The optical behavior of 1-10 is primarily dictated by the fluorenyl periphery. These compounds display strong blue fluorescent emission in solution and blue-green fluorescent emission in the solid state. Fluorescence lifetimes of all of these compounds are on the nanosecond timescale, and this suggests that the emission originates from the singlet excited state to the ground state. Intermolecular interactions in the solid state lead to considerable broadening of the emission bands.