Fluorescence studies on phenylene moieties embedded in a framework of periodic mesoporous organosilica

Abstract

The excited state characteristics of phenylene (Ph)-bridged periodic mesoporous organosilica (PMO) powders with crystal-like and amorphous wall structures are investigated. Crystal-like Ph-PMO has a molecular ordering of the bridging organic moieties with intervals of 0.76 and 0.44 nm parallel and perpendicular to the mesochannel direction, respectively, whereas amorphous Ph-PMO has no molecular-level periodicity in the wall. Fluorescence from the exciton and excimer of the Ph moieties and the defect center in the silicate network were detected at room temperature, but fluorescence from the excimer and the defect center were not detected at 77 K for crystal-like Ph-PMO dispersed in a methanol/ethanol mixed solvent. The decay curve of the exciton fluorescence of crystal-like Ph-PMO at room temperature was analyzed successfully using a one-dimensional diffusion model quenched by the defect center and the excimer site. The results were discussed in comparison with those for the crystal-like biphenylene-bridged PMO reported in the preceding paper (Yamanaka et al., Phys. Chem. Chem. Phys., 2010, 12, 11688-11696). The existence of excited states with various conformations including ground state dimers or aggregates of the Ph moieties was suggested for amorphous Ph-PMO. It was clearly apparent that the differences in the excited state dynamics reflected the differences in the molecular-level structure in the wall.

Stabilization of nanosized MgFe2O4 nanoparticles in phenylene-bridged KIT-6-type ordered mesoporous organosilica (PMO)

“…The intense absorption bands at 270 nm (4.6 eV) and 276 nm (4.5 eV) in absorption spectra and Tauc plots (Fig. 8) can be assigned to the aromatic phenylene bridges in the PMO network [14,86,87]. The spectra confirm that the hybrid materials contain phenylene bridge units.…”

Two‐Photon‐Excited Silica and Organosilica Nanoparticles for Spatiotemporal Cancer Treatment

“…Such systems include disulfide‐ and tetrasulfide‐doped PMO NPs (for glutathione‐mediated biodegradation in cells), and degradable oxamide‐ or lysine‐doped PMO NPs. Fourth, solid nonporous BS NPs can also be constructed from bridged multi‐organoalkoxysilanes (Figure D) . The absence of specific interactions between micelles and bridged organoalkoxysilanes produces dense NPs with high organic content in the composite matrix …”

Exciton migration dynamics between phenylene moieties in the framework of periodic mesoporous organosilica powder

“…The delocalization of the Ph exciton is consistent with the reported result; the excitation spectrum of crystal-like Ph-PMO shifts to a lower energy by about 500 cm 21 compared to that of BTEB due to the excitonic interactions between the Ph moieties. 15 The diffusion length of the Ph exciton (L Ph ) is calculated to be 4 nm at the lowest estimation, which suggests that the Ph exciton can move along approximately nine Ph moieties in Ph-PMO. The value of 4 nm is more than half of that in poly(p-phenylenevinylene) (7 ¡ 1 nm) 27 and more than quarter of that in the ladder-type poly(p-phenylene) (14 nm), 28 although phenylene moieties in Ph-PMO are unconjugated with each other.…”

“…where x is the distance from the surface, c(t) is the timedependent decay rate of the exciton-exciton annihilation of the Ph exciton, k Ph is the fluorescence decay constant of the exciton, c 0 (= C + E) is the quencher concentration, and k(t) is the quenching reaction rate of the Ph exciton by fixed C and E. 15 Eqn (6) can be resolved as follows:…”

“…[6][7][8][9] PMOs with a dense accumulation of bridging organic groups in their silica network have been found to exhibit unique photophysical, photochemical and electrochemical properties, based on their intermolecular interactions, such as rapid excimer formation, 10 enhanced electron donation 11,12 and hole transportation. 13,14 In our preceding paper, 15 we investigated the excited-state dynamics of the phenylene (Ph) moieties in Ph-PMO powder and obtained unique results regarding an excitation energy migration in the PMO framework. In detail, Ph-PMO had three emission bands due to the exciton of the Ph moieties (295 nm), the defect center in the silica network (303 nm) and the excimer of the Ph moieties (340 nm) upon excitation at 266 nm.…”