Biphenyl-bridged periodic mesoporous organosilicas: Synthesis and in situ charge-transfer properties

Abstract Using a novel cationic oligomer surfactant as the structure-directing agent, the fluorescent biphenyl-bridged periodic mesoporous organosilicas (BpUPMOs) were successfully synthesized through the cohydrolysis and cocondensation of 4,4′-bis(3-triethoxysilyl propylureido) biphenyl (BpUSi) and tetraethoxysilane (TEOS). The structure characterization of the samples was obtained by FT-IR spectra, small-angle X-ray scattering (SAXS), high resolution transmission electron microscopy (HRTEM), and nitrogen adsorption–desorption analyses. The results showed that ordered mesoporous structure was obtained below 40 mol% of the content of BpUSi. With the increase of the amount of BpUSi, the ordering degree of mesoporous structure of BpUPMOs decreased. Fluorescence emission spectra of BpUPMOX ( X is a mole fraction of BpUSi, 0%, 10%, 20%, 30%, 40%, 50%, respectively) showed gradually enhanced and red-shifted bands from 357 to 372 nm as X was less than 30 mol%. However, with further increase of X value, the bands at 359 nm for BpUPMO40 and at 354 nm for BpUPMO50 exhibited blue-shift compared with that of the sample BpUPMO30 (372 nm). This fluorescence phenomenon induced by the amount of organosilicone in the PMOs has not been reported. Furthermore, Charge-transfer (CT) complex composed of BpUPMO20 and decylviologen was obtained, in which the biphenyl groups were as electron donors in the pore walls and the decylviologen molecules were as electron acceptors in the mesochannels of BpUPMO. UV–vis diffuse reflectance spectra and fluorescence spectra showed the existence of CT complex. Besides, the color of CT complex was over a wide range from the salmon pink to red brown.