Flexible Alkylene Bridges as a Tool To Engineer Crystal Distyrylbenzene Structures Enabling Highly Fluorescent Monomeric Emission

Abstract

To design ultrabright fluorescent solid dyes, a crystal engineering strategy that enables monomeric emission by blocking intermolecular electronic interactions must be developed. We introduced propylene moieties in distyrylbenzene (DSB) as a bridge between the two phenyl rings around its C=C bonds. The bridged DSB derivatives formed compact crystals and exhibited emission colors similar to those of dilute solutions with high quantum yields. The introduction of flexible seven-membered rings into the DSB core resulted in moderate distortion and steric hindrance in the π-plane of DSB. However, the molecular arrangement could be controlled with almost no decrease in the crystal density relative to that of DSB, and the electronic interactions were suppressed. The crystal structure of bridged DSB was different from those of other DSB derivatives, indicating that bridging afforded novel crystalline systems. This design strategy has important implications in many fields and is more effective than conventional photofunctional crystal design strategies.