Ultralong Room-Temperature Phosphorescence Induced by H‑Bonding and π–π Interactions in Halogen-Free Carbazole Derivatives

Materials having room-temperature phosphorescence (RTP) are in limelight due to their advantageous long luminescence lifespan for applications in optoelectronics, bioimaging, and security purpose devices. Development of metal- and halogen-free organics for persistent luminescence and RTP has been envisaged through aggregation, heavy atom substitution, host–guest interactions, etc. In this article, we present experimental evidence for the effect of H-bonding and other nonbonding interactions on types of emission in five carbazole derivatives. An unsubstituted carbazole showed only fluorescence in powder form, while the N-aryl-substituted carbazole having carbonyl and nitrile groups (Benzal-CN-Cbz, Acph-CN-Cbz, and Bnph-CN-Cbz) showed dual emission consisting of fluorescence and phosphorescence in powder form under ambient conditions. Acph-CN-Cbz showed the longest excited-state lifetime exceeding 1.2 ms in powder form. RTP in Benzal-CN-Cbz, Acph-CN-Cbz, and Bnph-CN-Cbz is correlated to H-bonding and nonbonding interactions evident from single-crystal analysis. H-bonding involving the carbonyl group and extensive π–π interactions caused close packing in the solid state and is associated with the long-lived triplet excited state and RTP. Further, persistent luminescence having a lifetime of up to 1.5 s at ambient temperature in air was displayed in drop-casted PVA films. To the best of our knowledge, only a few organics, without halogen and heavy atoms, are available with such long lifetimes.具有室温磷光（RTP）特性的材料因其超长发光寿命在光电子学、生物成像及安防器件等领域展现出巨大应用潜力，因此受到广泛关注。通过聚集诱导、重原子取代、主客体相互作用等策略，开发兼具长余辉发光与室温磷光性能的无金属无卤素有机材料已成为学界研究热点。本文通过实验验证了氢键及其他非共价相互作用对五种咔唑衍生物发射类型的调控作用。未取代的咔唑在粉末态下仅表现出荧光发射；而带有羰基与腈基的N-芳基取代咔唑（包括Benzal-CN-Cbz、Acph-CN-Cbz及Bnph-CN-Cbz）在常温常压下的粉末态中可实现荧光与磷光的双重发射。其中，Acph-CN-Cbz的粉末态激发态寿命最长，超过1.2 ms。单晶分析结果表明，Benzal-CN-Cbz、Acph-CN-Cbz及Bnph-CN-Cbz的室温磷光特性与氢键及非共价相互作用密切相关：羰基参与的氢键与广泛的π-π相互作用促使固态下分子紧密堆积，进而催生长寿命三重激发态与室温磷光性能。此外，滴铸制备的聚乙烯醇（PVA）薄膜在常温空气环境中可实现长达1.5 s的长余辉发光。据我们所知，目前仅有少量无卤素、无重原子的有机材料可实现如此长的发光寿命。