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

• Published in: Journal of the American Chemical Society Vol. 140; no. 34; pp. 10848 - 10855
• Main Authors: Bharmoria, Pankaj, Hisamitsu, Shota, Nagatomi, Hisanori, Ogawa, Taku, Morikawa, Masa-aki, Yanai, Nobuhiro, Kimizuka, Nobuo
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 29.08.2018
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/jacs.8b05821

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 backbone prevent O2 inflow to the hydrophobic interior, as evidenced by long acceptor triplet lifetime of 4.9 ms. Air-stable TTA-UC was also achieved for gelatin with other nonionic surfactants (Tween 80 and Pluronic f127) and Triton X-100 with other gelling biopolymers (sodium alginate and agarose), demonstrating the versatility of current strategy.