Highly efficient deep-red/near-infrared D-A chromophores based on naphthothiadiazole for OLEDs applications

Donor-acceptor (D-A) chromophores are an important class of deep-red/near-infrared (DR/NIR) materials. However, efficient D-A DR/NIR fluorescent emitters are rare due to the intrinsic charge-transfer excited-state. In this paper, two novel D-A-type DR/NIR fluorescent emitters with triphenylamine (TPA, donor), naphthothiadiazole (NZ, acceptor), pyrimidine (2TPA-NZN) and benzene (2TPA-BZN) as the π-bridge, are designed and synthesized. The photophysical study and theoretical analysis revealed that the emissive-state of the two materials has hybridized local and charge-transfer (HLCT) characters. This characteristic caused high photoluminescent quantum yield (PLQY) both in solution and doped film. The 2TPA-BZN with a more rigid molecular structure exhibits a lower non-radiative rate constant (knr), resulting in relatively higher PLQY as compared with the 2TPA-NZN. The doped organic light-emitting diodes (OLEDs) devices based on these materials demonstrated excellent maximum external quantum efficiency (EQEmax > 5.0%) and the emission peak around 665 nm.