Synthesis of mesoporous aromatic silica thin films and their optical properties

Various aromatic-bridged periodic mesoporous organosilica (PMO) thin films were prepared from 100% organosilane precursors containing bridging organics of 1,4-phenylene (Ph), 4,4'-biphenylylene (Bp), 2,6-naphthylene (Nph), and 9,10-anthrylene (Ant) by an evaporation-induced self-assembly approach. Structural and optical properties of the films were characterized. Transparent films with periodic mesostructures were successfully obtained for all the compositions. The absorption spectra of the PMO films were similar to those of their precursors, indicating little interaction between the aromatic groups in the frameworks in the ground state, whereas the fluorescence spectra of the PMO films significantly red-shifted and also broadened compared with those of their precursors, suggesting excimer formation in the excited state. The quantum yields of the Ph-, Nph-, and Ant-PMO films were lower than those of their precursors by solid-state quenching. Exceptionally, the quantum yield increased above that of the precursor for the Bp-PMO film in spite of excimer formation. The high absorption coefficient (87000 cm-1) and high quantum yield (0.45) of the Bp-PMO film indicate its great potential for use as fluorescent materials.