Prolonging the phosphorescence lifetime of pure organic phosphorescent materials by a methyl-substitution strategy is described. We present a chemical strategy for improving the phosphorescence lifetime of triplet excitons under ambient conditions by incorporating methyl groups into the chemical structures. This is observed by a long-lived phosphorescence lifetime of up to 0.83 s detected for methylated 9-(4-(mesitylsulfonyl)phenyl)-9H-carbazole (3M), compared to 0.36 s for 9-(4-(phenylsulfonyl)phenyl)-9H-carbazole (0M) without any methyl groups. Additionally, enhanced phosphorescence efficiency can be obtained at an appropriate methylation degree, because of the smaller ΔE_ST (singlet and triplet energy gap) and ΔE_TT* (normal phosphorescence and long-lived phosphorescence energy gap). A comprehensive investigation on the packing mode in the crystalline state reveals that the methyl groups occupy the free volume and result in a suppression of non-radiative decay, accounting for the enhanced phosphorescence lifetime.

中文翻译：

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延长纯有机室温磷光寿命的甲基化效应†

描述了通过甲基取代策略延长纯有机磷光材料的磷光寿命。我们提出了一种化学策略，通过将甲基结合到化学结构中来提高环境条件下三重态激子的磷光寿命。甲基化 9-(4-(苯磺酰基)苯基)-9 H-咔唑 ( 3M )的长磷光寿命高达 0.83 秒，而 9-(4-(苯磺酰基) 的磷光寿命为 0.36 秒。苯基)-9 H-咔唑( 0M )，不含任何甲基。此外，由于 Δ E _ST较小，可以在适当的甲基化程度下获得增强的磷光效率（单重态和三重态能隙）和ΔE _TT*（正常磷光和长寿命磷光能隙）。对结晶态堆积模式的综合研究表明，甲基占据自由体积并导致非辐射衰减的抑制，从而提高了磷光寿命。