α-Cyanostilbene: a multifunctional spectral engineering motif

Abstract

Aggregation-induced emission (AIE) is a unique photophysical phenomenon of organic chromophores, exhibiting a significant emission enhancement in the condensed phase (aggregate/solid/film) than in the solution phase. This remarkable feature offers excellent strategies to obtain molecular materials possessing unique spectral signatures such as high fluorescence intensity, excellent quantum yield, large Stokes shift, and exquisite optoelectronic properties. Unlike a great library of articles with propeller-shaped tetraphenylethene molecular frameworks, reviews based on the mechanistic understandings of α-cyanostilbenes are relatively rare. Considering this, herein, we highlight the structure–property relationship of α-cyanostilbene-based AIE frameworks for tuning the aggregation through molecular displacement with reference to transition dipoles based on the following parameters: (i) positional substitution and orientation of the α-cyano unit, (ii) π-conjugation length (d_a or d_b), (iii) molecular size (DA_r) of the peripheral substitutions with respect to the α-cyano unit, and (iv) branching effect. In addition, we explain the utility of their unique AIE characteristics for various optoelectronic applications, including self-assembled nanostructures, chemical sensing, organogelation, white light emission, molecular switches, multiphoton absorption, liquid crystals, anion receptors, and biological probes. It is anticipated that organic materials with a cyanostilbene framework will continue to garner attention in the interdisciplinary fields of biology, chemistry, and materials science for diverse applications.