Endowing nitro-compounds with bright and stimuli-responsive luminescence based on propeller-like AIEgens

• Published in: Journal of materials chemistry. C, Materials for optical and electronic devices Vol. 9; no. 36; pp. 12177 - 12183
• Main Authors: Ding, Riqing, Qin, Ke, Sun, Huili, Zhou, Shasha, Guo, Sidan, Feng, Hui, Ma, Huili, Qian, Zhaosheng
• Format: Journal Article
• Language: English
• Published: Cambridge Royal Society of Chemistry 28.09.2021
• Subjects: Aromatic compounds; Charge transfer; Chromophores; Crystallography; Excitons; Fluorescence; Luminescence; Pi-electrons; Steric hindrance; Stimuli; Thermochromism
• ISSN: 2050-7526; 2050-7534
• DOI: 10.1039/d1tc01713f

An electron-rich nitro group, having higher sensitivity to various environments, is attractive for constructing stimuli-responsive luminescent materials. However, it also causes the fluorescence quenching of luminogens, making a formidable challenge to achieving intense luminescence in nitro-compounds. Herein, we design a group of bright nitro-compounds with high fluorescence efficiency, long-wavelength emission and multi-stimuli-responsive behaviors by combining through-space conjugated AIEgens and nitro groups. Two bright nitro-compounds were constructed by introducing a propeller-like skeleton with the π-conjugated rings, showing a strong intramolecular spatial delocalization of π-electrons. This character not only stabilizes the (π, π*) states to enable their energy below the n → π* transitions caused by the nitro groups, enormously hindering the intersystem crossing process and promoting radiative transition, but also provides a strong steric hindrance of aromatic rings to vastly restrict the nonradiative decay of the singlet excitons, thereby enabling a high fluorescence efficiency, up to 95%. Moreover, the propeller-like chromophore and the nitro group with strong electron-withdrawing capacity work in synergy to induce an environmentally responsive conversion of local excitation and charge transfer states, endowing these nitro-compounds with stimuli-responsive luminescence, including solvatochromism, thermochromism, and mechanochromism in a reversible way, which varies from green to red. These findings outline a fundamental principle for the construction of bright nitro-compounds with stimuli-responsive behaviors, endowing traditional nitro-compounds with new features for potential applications. An electron-rich nitro group, having higher sensitivity to various environments, is attractive for constructing stimuli-responsive luminescent materials.