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.

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A series of new cadmium complexes (dyes 1-5) were obtained by assembly of the donor-bridgeacceptor (D-π-A)-type ligand (L: 4′-(4-[4-(imidazole)styryl]phenyl) 2,2′ : 6′,2″-terpyridine) with CdX 2 (X=Cl, Br, I, NCS, ClO 4 ), in which dye 3 was characterized by single crystal X-ray diffraction. Various weak interactions, including hydrogen bonds (C-HÁ Á ÁN, C-HÁ Á ÁX) and π-π interactions, played significant roles in the final topological structures. Linear and non-linear optical properties of ligand and the complexes were investigated. The two-photon absorption cross-section of these complexes are larger than that of ligand with maximum values of 577 GM (dye 1), 242 GM (dye 2), 171 GM (dye 3), 326 GM (dye 4), and 215 GM (dye 5) in N,N-dimethylformamide. IntroductionMaterials with intense two-photon absorption (TPA) have received attention as the most promising candidates for novel optical materials; their variety of potential applications includes three-dimensional microfabrication [1], information technology [2], laser technology [3], biological system imaging [4], etc. However, the bottleneck of application of TPA materials is the generally small TPA cross-sections (δ). TPA is a third-order non-linear optical (NLO) phenomenon, and the efficiency of this process is determined by measuring δ values, which urged us to synthesize materials with large TPA cross-sections. Several strategies were proposed to improve TPA response, such as taking both intramolecular and intermolecular approaches to enhance TPA efficiency [5], connecting donor and acceptor symmetrically or unsymmetrically by π-conjugated bridges to form D-π-D, A-π-A, or D-π-A structures and the building of multibranched molecules [6], which can

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