Alkyl-Substituted Carbazole/Pyridine Hybrid Host Materials for Efficient Solution-Processable Blue- and Green-Emitting Phosphorescent OLEDs

Abstract: Three new pyridine-cored alkyl-substituted carbazole derivatives of 2,6-bis(2,7-dimethyl-9H-carbazol-9-yl)pyridine (2,7-MeCzPy), 2,6-bis(3,6-dimethyl-9H-carbazol-9-yl) pyridine (3,6-MeCzPy) and 2,6-bis(3,6-di-tert-butyl-9H-carbazol-9-yl)pyridine (3,6-tBuCzPy) were synthesized by means of connecting methyl or tert-butyl substituents on the 3,6 or 2,7 positions of carbazole with pyridine ring as the core. The influence of different alkyl and linkages mode on the thermal, photophysical, electrochemical properties and devices electrolumiescent (EL) performances of the compounds were comprehensively studied. In solution-processed blue or green phosphorescent organic light-emitting diodes (PHOLEDs) with bis[2-(4,6-difluorophenyl)-pyridinato-N,C²] picolinate iridium(III) (FIrpic) or fac-tris(2-phenylpyridine)iridium (Ir(ppy)₃) as phosphorescent dopants, EL performances follow the same sequence of 2,7-MeCzPy > 3,6-tBuCzPy > 3,6-MeCzPy, the trend is consistent with the value of triplet energies (E_T). Devices hosted by 2,7-MeCzPy achieving the best EL performance, exhibited maxima 13.6 cd A⁻¹ and 7.0 lm W⁻¹ for current efficiency (CE) and power efficiency (PE) in blue PHOLEDs, maxima 26.2 cd A⁻¹ and 16.2 lm W⁻¹ for CE and PE in green PHOLEDs. Graphic Abstract: [Figure not available: see fulltext.]