Synthesis and excited state modulation of organic blue light emitters based on 2,4,6-triphenyl-1,3,5-triazine and carbazole derivatives through ortho-positioned linking models

Abstract

Here, 9-(2-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)-9H-carbazole (OSTrPhCz) is used as a model emitter, and carbazole or 2-bromized carbazole is introduced into the ortho-positions of the 2,4,6-triphenyl-1,3,5-triazine framework to generate two emitters, namely OTrPhCz and OTrPhCzBr, which all show high thermal stability, obvious solvated bathochromic shift and aggregation-induced quenching. Their HOMO energy levels are determined as −5.83 eV for OTrPhCz, and −5.96 eV for OTrPhCzBr. Similarly, their LUMO energy levels are −2.88 eV for OTrPhCz and −2.71 eV for OTrPhCzBr. The introduction of bromine can widen the energy band gap of OTrPhCzBr by increasing the LUMO energy levels and decreasing the HOMO energy levels. The introduction of carbazole derivatives into the ortho-positions of the 2,4,6-triphenyl-1,3,5-triazine framework is helpful to produce single crystals, and the single crystals of OTrPhCz, OTrPhCzBr and OSTrPhCz are monoclinic, monoclinic and triclinic with space groups of P21/n, P21/n and P-1. The OTrPhCz and OTrPhCzBr solid powders are active in thermally activated delayed fluorescence. OTrPhCz and OSTrPhCz in crystal states exhibit obvious room temperature phosphorescence, and the phosphorescence lifetimes of the crystals are 47.18 ms for OTrPhCz and 463.08 ms for OSTrPhCz. The double substituted emitter OtrPhCz exhibits a higher fluorescence ability, and the single substituted emitter OSTrPhCz is a better RTP choice due to the symmetry breaking related H-aggregate of the OSTrPhCz crystal. The blue OLED of OTrPhCz as the guest shows a starting voltage, current efficiency, maximum emission brightness and external quantum efficiency of 4.2 V, 4.2 cd A⁻¹, 10389 cd m⁻² and 2.64%, respectively.