Rational Synthesis of Tetrahydrodibenzophenanthridine and Phenanthroimidazole as Efficient Blue Emitters and their Applications

Abstract

Ten luminophores based on tetrahydrodibenzophenanthridine (THDP) and phenanthroimidazole (PI) were designed, synthesized and characterized for their thermal, electrochemical, electro‐optical, charge‐transporting characteristics and electroluminescent properties. The blue luminophores exhibited high photoluminescence quantum yields of 66–93 % in toluene solutions and of 5–59 % in solid films. The highest values were observed for the derivative of THDP and PI containing methoxy group. The compounds showed close values of ionization potentials (5.74–6.11 eV) and electron affinities (2.71–3.06 eV). The selected compounds were tested in electroluminescent devices for the preparation of non‐doped light‐emitting layers. The best device fabricated using derivative of THDP and PI with methoxy groups showed blue electroluminescence with brightness of 10000 cd/m2 at high applied voltages. We performed DFT calculations and observed lowest singlet–triplet gap (ΔEST) values of 0.33 and 0.03 eV, oscillator strength (f) values of 0.034 and 0.008 for CN and NO2 derivatives. Interestingly, we also observed that compounds 3g and 3i showed HOMO and LUMO levels with similar energy gap (Eg) of 3.60 eV and deeper HOMO values of –5.30, –5.33 eV and LUMO values of –1.94, –2.77 eV.