Department of Chemistry and Biochemistry, Graduate School of Engineering, Center for Molecular Systems (CMS), Kyushu University , 744 Moto-oka, Nishi-ku, Fukuoka 819-0395, Japan.
J Am Chem Soc. 2015 Feb 11;137(5):1887-94. doi: 10.1021/ja511061h. Epub 2015 Jan 30.
Efficient triplet-triplet annihilation (TTA)-based photon upconversion (UC) is achieved in supramolecular organogel matrixes. Intense UC emission was observed from donor (sensitizer)-acceptor (emitter) pairs in organogels even under air-saturated condition, which solved a major problem: deactivation of excited triplet states and TTA-UC by molecular oxygen. These unique TTA-UC molecular systems were formed by spontaneous accumulation of donor and acceptor molecules in the gel nanofibers which are stabilized by developed hydrogen bond networks. These molecules preorganized in nanofibers showed efficient transfer and migration of triplet energy, as revealed by a series of spectroscopic, microscopic, and rheological characterizations. Surprisingly, the donor and acceptor molecules incorporated in nanofibers are significantly protected from the quenching action of dissolved molecular oxygen, indicating very low solubility of oxygen to nanofibers. In addition, efficient TTA-UC is achieved even under excitation power lower than the solar irradiance. These observations clearly unveil the adaptive feature of host gel nanofiber networks that allows efficient and cooperative inclusion of donor-acceptor molecules while maintaining their structural integrity. As evidence, thermally induced reversible assembly/disassembly of supramolecular gel networks lead to reversible modulation of the UC emission intensity. Moreover, the air-stable TTA-UC in supramolecular gel nanofibers was generally observed for a wide combination of donor-acceptor pairs which enabled near IR-to-yellow, red-to-cyan, green-to-blue, and blue-to-UV wavelength conversions. These findings provide a new perspective of air-stable TTA-UC molecular systems; spontaneous and adaptive accumulation of donor and acceptor molecules in oxygen-blocking, self-assembled nanomatrixes. The oxygen-barrier property of l-glutamate-derived organogel nanofibers has been unveiled for the first time, which could find many applications in stabilizing air-sensitive species in aerated systems.
超分子有机凝胶基质中实现了高效的三重态-三重态湮灭（TTA）基上的上转换（UC）。即使在空气饱和的条件下，有机凝胶中的供体（敏化剂）-受体（发射器）对也观察到强烈的 UC 发射，这解决了一个主要问题：受激三重态和 TTA-UC 被分子氧失活。这些独特的 TTA-UC 分子体系是由供体和受体分子在凝胶纳米纤维中自发聚集形成的，这些纳米纤维由发达的氢键网络稳定。通过一系列光谱、微观和流变学特性的研究，表明这些在纳米纤维中预组织的分子显示出高效的三重态能量转移和迁移。令人惊讶的是，纳米纤维中掺入的供体和受体分子受到溶解的分子氧淬灭作用的显著保护，表明氧气对纳米纤维的溶解度非常低。此外，即使在低于太阳辐照度的激发功率下，也能实现高效的 TTA-UC。这些观察结果清楚地揭示了主体凝胶纳米纤维网络的自适应特性，它允许供体-受体分子的高效和协同包含，同时保持其结构完整性。作为证据，超分子凝胶网络的热诱导可逆组装/解组装导致 UC 发射强度的可逆调制。此外，在超分子凝胶纳米纤维中观察到了空气稳定的 TTA-UC，对于广泛的供体-受体对组合都是如此，这使得近红外到黄色、红色到青色、绿色到蓝色和蓝色到紫外线的波长转换成为可能。这些发现为空气稳定的 TTA-UC 分子体系提供了一个新的视角；供体和受体分子在氧气阻断、自组装纳米基质中的自发和自适应积累。首次揭示了 L-谷氨酸衍生的有机凝胶纳米纤维的氧气阻隔性能，这在稳定充气系统中空气敏感物质方面可能有很多应用。
