A Quantum-Chemical Insight into the Role of Charge-Transfer States in Organic Emitters for Electroluminescence

The rapid progress of the design and development of efficient organic electroluminescent emitters without heavy transition metals has been achieved in recent experimental investigations. In this minireview, based on his recent theoretical works on purely organic emitters, the author provides a quantum-chemical insight into the role of charge-transfer (CT) electronic states in electroluminescence exploiting organic thermally activated delayed fluorescence (TADF) and radical emitters. The author discusses the electronic structure factors impacting the efficiencies of organic TADF and radical emitters, such as the characteristics of the singlet, doublet, and triplet excited states, the singlet-triplet energy gap, the spin-orbit coupling, the solid-state polarization effect, and the second-order spin-vibronic coupling mechanism in spin-flip processes. The author hopes thisminireviewwill be useful for further understanding of the photophysical mechanism and designing more novel and efficient organic electroluminescent materials (not limited to TADF and radical emitters).