The phenomenon of photon upconversion, in which a system absorbs two or more photons of lower energy and emits a photon of higher energy, has been used in numerous applications, including non-destructive bioimaging, deep-penetrating photodynamic therapy, catalysis, and photovoltaic devices. To date, photon upconversion has been observed typically in inorganic nanocrystals, nanoparticles, metal-organic frameworks (MOFs), supramolecular assemblies, and organic dyads. Herein, we have demonstrated a new strategy for harnessing photon upconversion-supramolecular upconversion-based on host-guest chemistry. We have identified a box-like fluorescent tetracationic host incorporating a thiazolothiazole emitter, which can accommodate a guest-sensitizer, 5,15-diphenylporphyrin inside its cavity and demonstrated that the host-guest inclusion complex displays triplet-fusion upconversion when the guest is excited with low energy light. The strategy of supramolecular upconversion has been employed successfully in two other host-guest complexes-with hosts comprised of anthracene emitters and a 5,15-diphenylporphyrin guest-corroborating the fact that this strategy is a general one and can be applied in designing a new family of host-guest complexes for photon upconversion. More importantly, supramolecular upconversion is accessible in solution under dilute conditions (μM) compared to most of the existing approaches that require significantly higher concentrations (mM) of emitters and/or sensitizers. Transient absorption spectroscopy and density functional theory have been employed in order to confirm a triplet-fusion upconversion mechanism. Host-guest complexation-mediated supramolecular photon upconversion eliminates multiple issues in relation to the existing systems related to high working concentrations, high incident laser power, and low optical penetration depths.

中文翻译：

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主客体复合介导的超分子光子上转换

光子上转换现象，其中系统吸收两个或多个较低能量的光子并发射较高能量的光子，已被用于许多应用，包括非破坏性生物成像、深穿透光动力疗法、催化和光伏器件. 迄今为止，通常在无机纳米晶体、纳米粒子、金属有机框架 (MOF)、超分子组装和有机二元组中观察到光子上转换。在此，我们展示了一种基于主客体化学的利用光子上转换-超分子上转换的新策略。我们已经确定了一种盒状荧光四阳离子主体，它包含一个噻唑噻唑发射体，可以容纳客体敏化剂 5，15-二苯基卟啉在其腔内，并证明当客体受到低能量光激发时，主客体包合物显示三重态融合上转换。超分子上转换策略已成功应用于另外两种主客体复合物——主体由蒽发射体和 5,15-二苯基卟啉客体组成——证实了这一策略是通用的，可用于设计新的用于光子上转换的主客体复合物家族。更重要的是，与需要显着更高浓度 (mM) 的发射体和/或敏化剂的大多数现有方法相比，在稀释条件 (μM) 下的溶液中可以进行超分子上转换。瞬态吸收光谱和密度泛函理论已被用来确认三重态融合上转换机制。主客体络合介导的超分子光子上转换消除了与现有系统相关的多个问题，这些问题与高工作浓度、高入射激光功率和低光学穿透深度有关。