Substitution Position and Vinylene Bond Geometry Modulating the Fluorescence Solvatochromism and Aggregation-Induced Emission of (9-Anthryl)vinyl(1-pyrenyl)vinylbenzene Isomers

Despite the lack of typical electron donor and acceptor in the molecule structure, a pure aromatic hydrocarbon, trans,trans-1-(9-anthryl) vinyl-4-(1-pyrenyl)-vinylbenzene (trans,trans-1,4-AVPVB), shows unusual fluorescence solvatochromism with emission shift over 80 nm. In addition, it displays an aggregation-induced emission (AIE) activity. For comparison, other three isomers, trans,trans-1,2-AVPVB, trans,trans-1,3-AVPVB, and trans,cis-1,4-AVPVB, were also synthesized. The effects of substitution position and vinylene bond geometry on solvatochromism, temperature-induced phase transition and AIE activity were systematically studied. Different from the other isomers, the as-prepared sample of trans,trans-1,2-AVPVB shows an endothermic peak and an exothermic peak before the melting point in the DSC curve. They correspond to a solid-to-gas transition and a solid-to-solid transition, respectively. Theoretical calculation indicates that the fluorescence solvatochromism may be related to the conformational change from the ground to the excited states. The solvatochromic degree is determined by conjugative effect. Trans,trans-1,2-AVPVB and trans,cis-1,4-AVPVB display moderate fluorescence solvatochromism. In contrast, the solvatochromic effect of trans,trans-1,3-AVPVB is weak due to meta-substitution. However, the conjugation interruption by meta-substitution is beneficial for solution emission, and trans,trans-1,3-AVPVB emits most efficiently in solution. Similar to trans,trans-1,4-AVPVB, trans,trans-1,2-AVPVB, and trans,cis-1,4-AVPVB also display an AIE behavior.