Simple and Versatile Platform for Air-Tolerant Photon Upconverting Hydrogels by Biopolymer–Surfactant–Chromophore Co-assembly

Exploration of triplet–triplet annihilation based photon upconversion (TTA-UC) in aqueous environments faces difficulty such as chromophores insolubility and deactivation of excited triplets by dissolved oxygen molecules. We propose a new strategy of biopolymer–surfactant–chromophore coassembly to overcome these issues. Air-stable TTA-UC with a high upconversion efficiency of 13.5% was achieved in hydrogel coassembled from gelatin, Triton X-100 and upconverting chromophores (triplet sensitizer and emitter). This is comparable to the highest UC efficiency observed to date for air-saturated aqueous UC systems. Moreover, this is the first example of air-stable TTA-UC in the form of hydrogels, widening the applicability of TTA-UC in biological applications. The keys are two-fold. First, gelatin and the surfactant self-assemble in water to give a developed hierarchical structure with hydrophobic domains which accommodate chromophores up to high concentrations. Second, thick hydrogen-bonding networks of gelatin...