Fluorescent hybrid with electron acceptor methylene viologen units inside the pore walls of mesoporous MCM-48 silica.

A fluorescent material with methylene viologen units bonded into the pore walls of the mesoporous MCM-48 silica is synthesized using the method of periodic mesoporous organosilicas with bridging groups (PMOs), in which the methylene viologen units are located within the channel walls through the cohydrolysis and cocondensation of dichloride of N,N'-bis(triethoxysilylmethyl)-4,4'-bipyridinium (VP) and tetraethoxysilane (TEOS). It is found that the suspension of the hybrid emits fluorescence at ca. 380 and 420 nm, which is attributed to the S(1) state (pi* --> pi) of the viologen and the charge-transfer complex between the bipyridinium units as electron acceptor and accompanying halide (Br(-), Cl(-)) as donor components, respectively. The fluorescent emission intensity increases with increasing the amount of the VP covalently bonded to MCM-48 framework. The fluorescent intensity of VP adsorbed on the surface of the pore channel of MCM-48 was greatly weaker than that of the hybrid MCM-48-VP at the same molar ratio of TEOS to VP. No fluorescence was observed for pure VP. The different fluorescent intensity is ascribed to the fact that restricted degree of the rotation between two pyridine rings is different. It could be prospected that this material is potentially applied in drug delivery and fluorescence probing for medical diagnosis and synchronous therapy.