Unique Electron Deficient Molecule for Thermally Activated Delayed Fluorescence Application

Utilizing purely organic materials with relatively highly emissive characteristics for designing organic light-emitting diodes (OLEDs) is fascinating since employing rare metals is unessential, hence, enormous research activities have been conducted in this field. Recently, additional efforts were devoted to designing special emitting materials demonstrating thermally activated delayed fluorescence (TADF). Molecular structures were ideally designed in a specific way using an electron-deficient molecule as an acceptor (A) and an electron-rich molecule as a donor (D) in order to minimize the overlapping between the highest occupied molecular orbital (HOMO) of the donor (D) and the lowest unoccupied molecular orbital (LUMO) of the acceptor (A). TADF requires a small band gap between the singlet excited and triplet excited states (ΔE_ST), usually less than (c.a 0.1 eV) of the luminescent material. This makes it possible to thermally harvest the excitons from the triplet excited state (T₁) to the singlet excited state (S₁) by a process known as reverse intersystem crossing (RISC) and then to harvest all the excitons for the fluorescence process. Thus, the design of the TADF molecular structure needs both an electron-rich segment as a donor and an electro-deficient segment as an acceptor. Up to the present, electron-deficient moieties (EDM) have been studied less than electron rich moieties (ERM) during the last few years. This review is highlighting the recent advances regarding the specific molecular designs of TADF emission materials for OLED applications, particularly, focusing on (dibenzothiophene-S,S-dioxide) as electron deficient molecule, which exhibits a strong electron-deficient unit and high ability of photo-and electroluminescence features.