A Highly Fluorescent cis‐Stiff‐Stilbene

Abstract

AbstractBecause of the ultrafast C=C bond torsion and electrocyclic reaction in the excited state, cis‐stilbenes are generally nonfluorescent (Φf <10−4) in common solvents at ambient temperature. The known examples of highly fluorescent cis‐stilbenes are limited to those with the C=C configuration structurally locked. Herein we report a novel cis‐stiff‐stilbene c‐2 a that displays a high fluorescence quantum efficiency up to 0.47 in acetonitrile (MeCN) without sacrificing the photoisomerization ability. Through comparison with the corresponding aminostilbene c‐1 and positional isomer c‐2 b, the fluorescence turn‐on for c‐2 a takes root in two structural origins: namely, a rigid stilbene backbone that suppresses the cis→dihydrophenanthrene (DHP) photocyclization and a non‐twisted meta‐N,N‐dimethylamino (DMA) substituent that slows down the cis→trans photoisomerization. The corresponding trans isomers t‐1, t‐2 a, and t‐2 b are also investigated to gain insights into the meta‐DMA effect in stiff‐stilbene.