Aggregation-Induced Fluorescence Behavior of Triphenylamine-Based Schiff Bases: The Combined Effect of Multiple Forces

Eight triphenylamine (TPA)-based
Schiff bases that exhibit different
aggregation-induced emission (AIE) or aggregation-caused quenching
(ACQ) behavior in tetrahydrofuran (THF)/water mixtures have been synthesized
and characterized. The photophysical properties in solution, aqueous
suspension, film, and the crystalline state along with their relationships
were comparatively investigated. The single-crystal structures of 1–8 indicate that compact π···π
stacking or excimers induce fluorescence quenching of 1, 2, 5, and 7. However, the
existence of J aggregates or multiple intra- and
intermolecular interactions restrict the intramolecular vibration
and rotation, enabling compounds 3, 4, 6, and 8 to exhibit good AIE character. The size
and growth process of particles with different water fractions were
studied using scanning electron microscopy, which demonstrated that
smaller uniformly dispersed nanoparticles in the THF/water mixtures
favor fluorescence emission. The above results suggest that the combined
effects of multiple forces caused by structural variation have a great
influence on their molecular packing, electronic structure, and aggregation-induced
fluorescence properties. In addition, piezofluorochromic experiments
verified the potential applications of 4 and 6.