A Twisted Phosphor: Breaking T₁ Energy Conservation in Dopant‐Matrix Organic Phosphorescence Systems

Abstract In the exciton model of organic compounds proposed by Kasha, energy levels of T₁ states are insensitive to microenvironment because of negligibly small transition dipole moments of T₁ states. This phenomenon of T₁ energy conservation holds true in most organic systems. Here a serendipitous finding of a twisted organic phosphor that breaks T₁ energy conservation in dopant‐matrix phosphorescence systems is reported. Specifically, the twisted phosphor exhibits distinct phosphorescence colors and T₁ energy levels when doped into different organic matrices under ambient conditions. Time‐dependent density functional theory calculations reveal that, when the twisted phosphor is in its freely rotating form, the increase of twisted angle leads to the increase of its T₁ energy level. After being planarized by alkyl cyclization, the phosphor shows the recovery of T₁ energy conservation. Owing to its sensitive T₁ level, the twisted phosphor functions as label‐free and visual probe for direct observation of polymer phase separation.