Light-induced open-loop products from a triphenylamine-functionalized π-conjugated pillar[5]arene and radical fluorescence emission†

Pure organic luminescent radicals are of great importance in photoelectromagnetic materials. Designing and synthesizing novel radical systems with luminescence properties has always been a challenging task. Herein, we designed a pillar[5]arene-based π-conjugated macrocycle molecule (P5NA) capable of producing intriguing photochromic phenomena in chloroform solution, resulting in an open-loop biradical system (P5NA²˙) with unique fluorescence emission. The formation of the biradical luminescent system was confirmed using a range of analytical techniques, including UV/Vis absorption and fluorescence spectroscopy, electron paramagnetic resonance (EPR) spectroscopy, ¹H NMR, and density functional theory (DFT) calculations. This study provides a new paradigm for the design and synthesis of macrocycle molecule-based radical systems with luminescent properties.