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.
Six D-π-A model compounds (compounds 1-6) were conveniently synthesized and characterized by H NMR,C NMR, MS and single crystal X-ray diffraction. One photon absorption and emission properties were studied by using a series of UV-visible and fluorescence spectra and theoretical calculations were applied to investigate the structure-property relationships, which showed that all six compounds possessed an obvious intramolecular charge transfer process which could be attributed to their optical properties. We simultaneously investigated their fluorescence emission performance in water/acetonitrile mixtures and found that they all have outstanding aggregation induced emission properties. Scanning electron microscopy testing illustrated that orderly aggregation was the main reason for their aggregation induced emission properties. Cytotoxicity tests indicated that all these compounds had good biocompatibility for living cells, and bio-imaging studies highlighted the potential application of the six compounds in one-photon fluorescence microscopy imaging domains.
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