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 AIE 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 intramolecular 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.