Novel electro-fluorescent materials with hybridized local and charge transfer (HLCT) excited state for highly efficient deep red to near-infrared OLEDs

Abstract

Deep red (DR) and near-infrared (NIR) fluorescent emitters are often plagued by design difficulties due to the strong intramolecular interaction. Herein, two new DR and NIR molecules, 4-(7-(10-ethyl-10H-phenoxazin-3-yl)benzo[c][1,2,5]thiadiazol-4-yl)-N,N-diphenylaniline (TPAC2) and 4-(9-(10-ethyl-10H-phenoxazin-3-yl)naphtho[2,3-c][1,2,5]thiadiazol-4-yl)-N,N-diphenylaniline (TPANZC2), characteristic with hybrid local and charge transfer were achieved via iteration with a theoretical combined experimental method. Both emitters realized the reverse intersystem crossing (RISC) via the hot exciton channel. As results, the non-doped organic light-emitting diodes (OLEDs) of TPAC2 and TPANZC2 achieved the maximum external quantum efficiency (EQEmax) of 2.4% at 680 nm and 1.1% at 755 nm, respectively. Both conspicuous upward EQE curves demonstrated excellent resistance to efficiency roll-off. The ternary co-doping system further unleashed the potential in NIR emission, the co-doped device with 5 wt% TPANZC2 achieved an EQE of 4.6% with emission at 724 nm, which is among the best results of HLCT-NIR fluorescent OLEDs to date.