Rapid construction of bicyclic triazoline skeletons with dual-state emission via cycloaddition reaction of 4-phenyl-1,2,4-triazoline-3,5-dione with vinyl azides

Abstract

Herein, a novel metal-free strategy for the construction of deep-blue emissive bicyclic triazolines has been developed that utilizes a cycloaddition reaction (rate constants up to 134 M⁻¹ s⁻¹) of 4-phenyl-1,2,4-triazoline-3,5-dione with vinyl azides. The resulting bicyclic triazoline frameworks possess remarkable photophysical properties, including high photoluminescent quantum yields (PLQYs) and fluorescence enhancement. Strong blue emissions are easily observed under UV light illumination both in solution and the solid state, giving high PLQYs of 78% and 87%, respectively. Moreover, the bicyclic triazolines have Commission Internationale de l'Eclairage coordinates of (0.15, 0.10), which possess great potential for the development of new blue luminescent materials. Time-dependent density-functional theory calculations revealed that the S₁ → S₀ transition with a large oscillator strength had a vital effect on the high fluorescence quantum yields of the bicyclic triazolines. Furthermore, crystallographic analysis elucidated that the differences in the quantum yield of the bicyclic triazolines in the solid state was related to molecular π-stacking in different conformations. Meanwhile, the excellent stability and low cytotoxicity of the bicyclic triazolines also allowed them to be utilized as a fluorescent probe for live-cell imaging, broadening the bio-imaging toolkits available to researchers.