A Highly Efficient Propeller‐like Organic Radical with Less Solvent Sensitivity and Selective Detection of Aromatic Amines from Aliphatic Amines through Turn‐on Fluorescence

Highly efficient red luminescent organic radicals with less solvent sensitivity are much more attractive due to their wide application in various fields, especially in fluorescence sensing, and bioimaging. In this work, we synthesized a three δ‐carboline‐capped highly efficient propeller‐like organic radical TTM‐3δPyID with a D‐A structure. The radical showed pure red emission with PLQY of 77.3% in cyclohexane and kept 35.2% even in the polar solvent dichloromethane, indicating potential applications in fluorescence sensing. Radical TTM‐3δPyID also showed stepwise proton‐responsive properties and different emissions at the different states. Furthermore, by taking advantage of the nitrogen site of the radical, we have achieved a fluorescent‐quenched radical derivative TTM‐3δPyID‐AB by introducing of 2‐bromoethyl chain through a quaternary ammonium salt reaction. The radical TTM‐3δPyID‐AB showed turn‐on fluorescence in the presence of primary organic amines. Finally, this turn‐on fluorescent property is successfully used to distinguish aliphatic amines from aromatic amines.