Solvent-induced polymorphism, thermally activated delayed fluorescence, and mechanochromic luminescence of a single compound

Abstract

A newly synthesized organic compound, 4,5,6,7-tetrakis-carbazol-9-yl-2-methyl-isoindole-1,3-dione (4CzPTANMe) exhibits polymorphism, mechanochromic luminescence, and thermally activated delayed fluorescence (TADF), simultaneously. 4CzPTANMe exists six solvent-induced aggregation states including five crystalline forms with fluorescence emission from green to red. Interestingly, 4CzPTANMe shows typical TADF characteristics in crystalline states while no TADF property in disordered amorphous state. Crystal structure analysis together with photophysical measurements reveal that the polymorph-dependent TADF of 4CzPTANMe can be facilely tuned by the solvents in the crystals. In addition, a doped light-emitting device based on 4CzPTANMe as an emitter exhibits greenish-yellow emission with a peak at 538 nm, a maximum current efficiency of 15.9 cd/A and a decent external quantum efficiency of 5.96%.