Recent Progress in Photon Upconverting Gels

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.

Visible‐to‐Ultraviolet Light Conversion: Materials and Applications

“…One strategy to avoid this problem is to use viscous droplets, polymers, or co‐assembly of molecular groups as oxygen barriers. [ 49,60 ] However, these methods inevitably slow the diffusion of TTA chromophores or deactivate triplet states and therefore lead to a reduced quantum yield. Third, the TTA process is unlikely to realize deep UV emission due to the limited acceptor singlet energies and strong UV absorptions of organic chromophores and solvents.…”

Photon Upconversion Hydrogels for 3D Optogenetics

“…In order to develop photoactive biomaterials that operate by TTA‐UC, it is important to consider the characteristics of the multiexciton system together with the mechanism of upconversion, which has been extensively described in the literature (schematically detailed in Figure S1, Supporting Information). [ 27,28 ] Previous studies have shown that TTA‐UC hydrogels can be synthesized, but none have reported hydrogels containing cells dispersed within a 3D scaffold. [ 15,29 ] In a recent eloquent study, Pluronic‐based gels were simply used as a light source (NIR‐to‐blue light) placed above 2D cultures of hippocampal neurons to trigger optogenetic responses.…”

“…However, we note that similar optogenetic responses can be observed in 2D cultures by direct irradiation with blue light. [ 7 ] To obtain biocompatible, cell‐laden TTA‐UC hydrogels, we sought to integrate the sensitizer/annihilator pairs within the core of oil‐in‐water emulsion droplets [ 24,25,28,30,31 ] that could be incorporated into cell‐laden hydrogel matrices (e.g., fibrin gels). Several requirements must be met so that the photoinduced processes can efficiently lead to the desired optogenetic response(s).…”

Development of the sensitizer for generating higher-energy photons under diluted condition via the triplet-triplet annihilation-supported upconversion

“…This phenomenon is called as triplet-triplet annihilation (TTA, Scheme 1). [6][7][8][9] By selecting the types of sensitizers and emitters, the wavelengths of the acceptable incident and the generated light can be tuned. [6][7][8][9] Indeed, TTA-supported upconversion systems have been applied for in vivo imaging.…”

“…[6][7][8][9] By selecting the types of sensitizers and emitters, the wavelengths of the acceptable incident and the generated light can be tuned. [6][7][8][9] Indeed, TTA-supported upconversion systems have been applied for in vivo imaging. [10][11][12][13][14][15][16] In particular, since UV light, which is favourable for inducing photo-activation into prodrugs, can be generated, TTA-supported upconversion is regarded as a promising tool for realizing phototherapy inside bodies.…”