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.

Aggregation Behavior and High Charge-Carrier OFET-Mobility of Functionalized Phenanthro[9,10-d]imidazoles

“…Thus, it results in achieving more balanced carrier mobilities . PI acts as an electron acceptor when linked to the electron-donor moiety, thus forming bipolar materials. ,,− Deprotonation of the −NH group of the imidazole moiety allows attaching a wide variety of substituents and can modulate π–π stacking and molecular interactions in the solid state.…”

“…The packing pattern of the active layer decides the intermolecular interactions involved and thus the degree of the charge carrier . In the field of organic light-emitting diodes, phenanthro­[9,10- d ]­imidazoles (PIs) have gained immense interest with respect to high device efficiency (external quantum efficiency), low turn-on voltage, perfect color purity (CIE), and slight efficiency roll-off. − However, the OFET behaviors of PIs are not explored. Because of their unique electronic nature, they can be promising candidates for device fabrication. − The aim of the work is to functionalize PI with electron-donating groups to study the solid-state emission and OFET behavior.…”