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.