Garain Swadhin, Shoyama Kazutaka, Ginder Lea-Marleen, Sárosi Menyhárt, Würthner Frank
Institut für Organische Chemie, Universität Würzburg, 97074 Würzburg, Germany.
Center for Nanosystems Chemistry (CNC), Universität Würzburg, 97074 Würzburg, Germany.
J Am Chem Soc. 2024 Aug 7;146(31):22056-22063. doi: 10.1021/jacs.4c07730. Epub 2024 Jul 24.
Activating delayed fluorescence emission in a dilute solution via a non-covalent approach is a formidable challenge. In this report, we propose a strategy for efficient delayed fluorescence generation in dilute solution using a non-covalent approach via supramolecularly engineered cyclophane-based nanoenvironments that provide sufficient binding strength to π-conjugated guests and that can stabilize triplet excitons by reducing vibrational dissipation and lowering the singlet-triplet energy gap for efficient delayed fluorescence emission. Toward this goal, a novel biphenyl bisimide-derived cyclophane is introduced as an electron-deficient and efficient triplet-generating host. Upon encapsulation of various carbazole-derived guests inside the nanocavity of this cyclophane, emissive charge transfer (CT) states close to the triplet energy level of the biphenyl bisimide are generated. The experimental results of host-guest studies manifest high association constants up to 10 M as the prerequisite for inclusion complex formation, the generation of emissive CT states, and triplet-state stabilization in a diluted solution state. By means of different carbazole guest molecules, we could realize tunable delayed fluorescence emission in this carbazole-encapsulated biphenyl bisimide cyclophane in methylcyclohexane/carbon tetrachloride solutions with a quantum yield (QY) of up to 15.6%. Crystal structure analyses and solid-state photophysical studies validate the conclusions from our solution studies and provide insights into the delayed fluorescence emission mechanism.
通过非共价方法在稀溶液中激活延迟荧光发射是一项艰巨的挑战。在本报告中，我们提出了一种策略，通过基于超分子工程的环番纳米环境，采用非共价方法在稀溶液中高效产生延迟荧光，该纳米环境为π共轭客体提供足够的结合强度，并通过减少振动耗散和降低单重态-三重态能隙来稳定三重态激子，以实现高效的延迟荧光发射。为了实现这一目标，引入了一种新型的联苯双酰亚胺衍生的环番作为缺电子且高效的三重态产生主体。当各种咔唑衍生的客体被封装在该环番的纳米腔内时，会产生接近联苯双酰亚胺三重态能级的发射性电荷转移（CT）态。主客体研究的实验结果表明，高达10 M的高缔合常数是在稀释溶液状态下形成包合物、产生发射性CT态和稳定三重态的先决条件。通过不同的咔唑客体分子，我们可以在甲基环己烷/四氯化碳溶液中，在这种咔唑封装的联苯双酰亚胺环番中实现可调谐的延迟荧光发射，量子产率（QY）高达15.6%。晶体结构分析和固态光物理研究验证了我们溶液研究的结论，并为延迟荧光发射机制提供了见解。
