Chiral Blue TADF Materials Enhance the Spin Transitions to Improve Emission Quantum Yield

Circularly polarized thermally activated delayed fluorescence materials not only possess high exciton utilization efficiency but also have the capability to emit circularly polarized light for potential information storage and sensing. In this work, chiral blue TADF enantiomers are prepared. The energy difference between singlet and triplet, ΔE_ST, increases with the strength of chirality. The chiral orbit-induced spin degeneracy elimination could enhance spin relaxation, where spin could flip easily to lead to an effective transition from triplet to singlet states. This induces a pronounced enhancement in fluorescence quantum yield. Furthermore, circularly polarized emission of chiral TADF materials under different external magnetic fields are studied. Magnetic field control of g_lum presents a mirror symmetry effect for chiral TADF enantiomers, which provides evidence for the transition between the photon spin and electron spin.