Relaxation Dynamics and Structural Characterization of Organic Nanobelts with Aggregation-Induced Emission

We prepared the fluorescent nanobelts of cyano-substituted 1,4-distyrylbenzene derivative (CNDSB) with the reprecipitation method. CNDSB is nonemissive in solution but with strong aggregation-induced emission (AIE) in belt-like structure. The molecular structure predicted by quantum chemical calculations indicates a twisted conformation of CNDSB monomer, while the solid-state X-ray structure of the CNDSB crystal features herringbone-type arrangement and three benzene rings arrange in nearly planar conformation. Femto- and picosecond time-resolved fluorescence spectroscopy are implemented to study the photophysics and the origin of the ME effect in CNDSB nanobelts. The fluorescence quenching of CNDSB in THF solution arises from the efficient nonradiative isomerization channel. In this study, the fluorescence decay of CNDSB embedded in poly(methyl methacrylate) matrix is slowed down due to the restriction of intra:molecular motions in the solid matrix. In nanobelt structure, the fluorescence lifetime further increases due to the intermolecular interaction between H-type aggregates. Both the steady-state and time-resolved studies suggests that there are at least two different packing structures might exist in nanobelts, and the relative composition of these two different structures gradually changes in different sizes of nanobelts.