Abstract
Recent progress in the development of gels showing triplet-triplet annihilation based photon upconversion (TTA-UC) is reviewed. Among the two families of upconverting gels reported, those display TTA-UC based on molecular diffusion show performances comparable to those in solutions, and the TTA-UC therein are affected by dissolved molecular oxygen. Meanwhile, air-stable TTA-UC is achieved in organogels and hydrogels by suitably accumulating TTA-UC chromophores which are stabilized by hydrogen bonding networks of the gelators. The unique feature of the air-stable upconverting gels is that the self-assembled nanostructures are protected from molecular oxygen dissolved in the microscopically interconnected solution phase. The presence of the bicontinuous structures formed by the upconverting fibrous nanoassemblies and the solution phase is utilized to design photochemical reaction systems induced by TTA-UC. Future challenges include in vivo applications of hydrogels showing near infrared-to-visible TTA-UC.
Highlights
The excited triplet state plays pivotal roles in a variety of photofunctional systems
The triplet annihilation-based photon upconversion (TTA-UC) typically occurs in multi-chromophore systems, which is initiated by triplet energy transfer (TET) from a photo-excited donor to an acceptor via an electron exchange (Dexter energy transfer) mechanism
The performance of molecular diffusion-based in gels was found to be comparable to that performance of molecular diffusion-based triplet annihilation (TTA)-UC in gels was found to be comparable to that in in solutions
Summary
The excited triplet state plays pivotal roles in a variety of photofunctional systems. The excited triplet states are susceptible to deactivation by molecular oxygen (3 O2 ) [16,17], and their protection from oxygen is an outstanding issue in triplet-related photochemical processes [18] This holds true for TTA-UC, and it has been investigated by completely deaerating the solutions or solid materials followed by the sealing procedures. The molecular diffusion-based TTA-UC avoiding the contact between excited triplet states and oxygen molecules. The via triplet energy migration in densely inevitable oxygen quenching in air-saturated gels. The TTA-UC via triplet energy organized chromophore assemblies can be efficient even in can air-saturated gels. The structure of molecular assemblies plays a crucial role in reducing the participation and gels that areofrequired to avoid triplet diffusion molecular oxygenthe inside gelsquenching. It will contribute to the design design of gelator structures to block molecular and to achieve efficient of gelator structures to block molecular oxygen oxygen and to achieve efficient in air. in air
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