Oxygen heterocyclic coumarin-based hybridized local and charge-transfer deep-blue emitters for solution-processed organic light-emitting diodes

Abstract

Hybridized local and charge-transfer (HLCT) emitters have raised great expectations in organic light-emitting diodes (OLEDs) on account of their capability to enhance light-emitting efficiency via the employment of “hot excitons”. Herein, three novel blue HLCT materials, 6-(bis(4-(3,6-di-tert-butyl-9H-carbazol-9-yl)phenyl)amino)-3-phenyl-1H-isochromen-1-one (BCz-6P), 6-([1,1′-biphenyl]-4-yl(9,9-dimethyl-9H-fluoren-2-yl)amino)-3-phenyl-1H-isochromen-1-one (pPh-6P), and 6-([1,1′-biphenyl]-2-yl(9,9-dimethyl-9H-fluoren-2-yl)amino)-3-phenyl-1H-isochromen-1-one (oPh-6P), employing oxygen-containing heterocyclic coumarin derivatives as electron acceptors with good thermal stability and solubility, were designed and synthesized for the first time. The HLCT properties of these emitters were demonstrated through density-functional theory (DFT) calculations and natural transition orbital (NTO) analyses, combined with the photophysical properties of the materials. The films with 10 wt% emitters doped in the host material mCP exhibited blue emission at 448, 451, and 441 nm, respectively. The solution-processed deep-blue OLEDs based on oPh-6P achieved a maximum external quantum efficiency (EQE_max) of 5.78%, with Commission Internationale de L’Eclairage (CIE) coordinates of (0.16, 0.09). The best device with BCz-6P as the dopant achieved a maximum current efficiency (CE_max) of 7.37 cd A⁻¹, an EQE_max value of 6.80%, and an exciton utilization efficiency (EUE) of 64% through the “hot exciton” channel. The results reveal that coumarin derivatives serve as outstanding acceptors for constructing high-performance blue HLCT materials to develop solution-processed efficient deep-blue OLEDs.