General Synthetic Approach toward Geminal-Substituted Tetraarylethene Fluorophores with Tunable Emission Properties: X-ray Crystallography, Aggregation-Induced Emission and Piezofluorochromism

A general approach to the design and synthesis of a new series of geminal-substituted tetraarylethene (g-TAE) chromophores with aggregation-induced emission (AIE) properties has been developed via Corey–Fuchs reaction and subsequent Suzuki/Stille coupling reactions. To demonstrate the synthetic simplicity and versatility of this approach, fluorophores with diverse electronic characteristics have been synthesized. The validation of the geminal structure and bulky steric effect on the bond lengths and dihedral angles is further confirmed by the X-ray crystallography of three chromophores. With respect to single crystals of 2,2′-(2,2-diphenylethene-1,1-diyl)-dinaphthalene (DPDN 2 ), 1,1′-(2,2-diphenylethene-1,1-diyl)-dinaphthalene (DPDN 1 ), and 9,9′-(2,2-diphenylethene-1,1-diyl)dianthracene (DPDAn), intensive cofacial π–π stacking is absent in their molecular packing. The pseudopolymorphism of DPDAn crystals associated with different photoluminescence properties is investigated. In comparison to the solvent-free DPDAn crystal, the solvated DPDAn with embedded methanol or dichloromethane leads to some non-negligible conformational and packing alterations, which accounts for its distinct fluorescence properties. The AIE phenomena and optical properties of g-TAEs are probed with respect to steric and electronic effects. Along with their electrochemical characteristics and piezofluorochromism, our work has elucidated that this general approach can be utilized to develop a promising class of TAE materials for systematic investigations of its optoelectronic properties and crystal engineering.