Phenoxazine and Phenothiazine Quinoline Conjugates Delayed Fluorescence via Endothermic and Exothermic Reverse Intersystem Crossings White Light Emission and OLEDs

Abstract

The first part of the chapter describes delayed fluorescence (DF) due to the involvement of an endothermic reverse intersystem crossing (EN-RISC) and the mechanisms involved in harvesting 100% triplet excitons utilizing these processes. Adopting the DF mechanism via EN-RISC (TADF), many organic blue-, green-, and red-TADF systems that have been designed by various researchers are discussed. The phosphorescence mechanism is described in the second section of this chapter. The spin-forbidden intersystem crossing (ISC) mechanism, spin-orbit coupling (SOC), and El-Sayed rule are briefly described and addressed in this section. Numerous approaches, for example, hetero atom (N, O, S) and halogen substitutions in the molecular backbone, aggregation-induced emission, host-guest study, crystallization, and charge transfer complexation have been described in-depth to generate room-temperature phosphorescence (RTP) at ambient conditions. The third section of the chapter discusses various reports of simultaneous emissions via TADF (via EN-RISC) and RTP at ambient conditions. In the fourth part of the introduction chapter, white light emission from single-component (SCWLE) as well as multi-component organic systems has been discussed. In this part, the examples of white light emitters with dual-TADF (multi-component), dual-RTP (SCWLE), simultaneous fluorescence, and TADF features considering Dexter energy transfer (DET) have been adopted. The last section of the chapter reveals a new DF approach (EXDF: DF via an exothermic RISC process, EX-RISC). To realize EXDF, an energy inversion of S1 and T1 with a low energy gap (IST) between the states (violation of Hund s spin multiplicity rule) is required to suppress the quenching of the sensitive T1 state. In this part, examples of some molecules (especially phenalene analogs; cyclic azine, and heptazine) with an inverted lowest singlet-triplet gap (and#61485;and#916;and#119864;and#119878;and#119879;,and#61472;theoreticaland#61472;andand#61472;experimental studies) have been adopted. newline