Microscopic Structure and Mobility of Guest Molecules in Mesoporous Hybrid Organosilica: Evaluation with Single-Molecule Tracking

Single-molecule tracking (SMT) was applied to the evaluation of a microscopic heterogeneous structure by observing the diffusivity of guest molecules in phenyl-bridged periodic mesoporous organosilica films with one-dimensional (1D) nanoscale channels filled with template surfactant micelles. SMT clearly visualized the trajectories of individual fluorescence dyes, N,N′-dipropyl-1,6,7,12-tetrakis(4-tert-butylphenoxy)-3,4,:9,10-perylenetetracarboxdiimide (BP-PDI) and N-(2,6-diisopropylphenyl)-N′-(n-octyl)-terrylene-3,4:11,12-tetracarboxidiimide (TDI), encapsulated in the channels of the mesoporous material. The 1D trajectory indicated successful formation of bundled channel structures and encapsulation of the guest molecules into the channels. The encapsulation ratio of the guest dyes was strongly dependent on template surfactants. The difference was discussed in terms of the affinity between the guest molecules and surfactants. Statistical analysis for the diffusion of the guest molecules also revealed that diffusion coefficient in the channels was strongly dependent on the guest molecules and surfactants. The validity and applicability of the present approach for elucidation of a microscopic structure was discussed on the basis of the comparison between the trajectories of BP-PDI and TDI in the same sample.