Regulation of excited-state properties of dibenzothiophene-based fluorophores for realizing efficient deep-blue and HLCT-sensitized OLEDs

Efficient and multifunctional deep-blue organic luminescent materials are in great demand for the development of organic light-emitting diodes (OLEDs) in the application of ultrahigh-definition displays with a wide color gamut and highly saturated color. Herein, two deep-blue hybridized local and charge-transfer (HLCT) dibenzothiophene-phenanthroimidazole fluorophores were designed and synthesized by regulating the electron-withdrawing abilities of anchoring groups (phenyl and cyanophenyl) at the phenanthroimidazole unit. Computational and photophysical investigations reveal that the introduction of a cyano-group can finely modulate the component of excited states while maintaining similar luminescence colors. Consequently, the resulting non-doped devices show electroluminescence peaks at 451 and 452 nm with the Commission Internationale de l'eclairage (CIE) coordinates of (0.152, 0.067) and (0.153, 0.064). Based on HLCT-sensitized fluorescence and phosphorescence, high external quantum efficiencies (EQEs) of 7.08% and 27.30% and low efficiency roll-off are achieved concurrently at low doping concentrations. Moreover, a high-performance hybrid warm-white OLED with an EQE of 26.56% is obtained using the incomplete energy transfer process.