Regioselective synthesis of multifunctional dibenzo-heterocyclic dihydrophenazine derivatives: tunable excited-state structural relaxation and efficient red OLED host materials

Abstract

Heteroatom incorporation is a key strategy for tuning optoelectronic properties via electronic structure modulation. This study demonstrates that integrating spatial orientation and steric effects further extends this tunability. We report the regioselective C–N oxidative coupling of dihydrophenazine derivatives, yielding DPAC-h and DPAC-w series with distinct intramolecular environments. Condensed Fukui Function (CFF) analysis reveals that regioselectivity is driven by the preferential coupling of NH groups with electron-rich sites. We found that heterocyclic electronic effects, steric hindrance, and heteroatom orientation collectively govern excited-state structural relaxation, directly influencing the number of emission (single or dual) and energy levels. This mechanism is supported by fs-TA spectroscopy and theoretical calculations. Finally, guided by the principle of energy level matching, the optimized host DPAC-w-3,4-DBT enabled pure red OLEDs (624 nm) with a narrow FWHM of 48 nm and an EQE_max of 10%. This work transcends conventional heteroatom doping by synergizing electronic effects with spatial orientation, providing a predictive framework to manipulate excited-state dynamics and high-purity red OLEDs.