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

Abstract

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 O 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.

Annihilator dimers enhance triplet fusion upconversion

“…In recent years this process has received a surge of interest for its potential in solar energy applications 8. As a result, much work has been done to optimize upconversion in highly ordered and condensed systems, where there are large numbers of annihilators in very close proximity, thus leading to high upconversion efficiencies 9. Considering that upconversion can also greatly benefit other areas, such as imaging10 and photochemistry,2,11 where lower concentrations are required, a major challenge remains to find efficient upconverting materials that are robust with respect to concentration level.…”

Hydrogels: soft matters in photomedicine

“…7b). 286 At the other end of the spectrum, photochemistry may be employed in the construction of the hydrogel backbone. E.g., photo cross-linked polymeric PEG materials with terminal anthracene moieties (26) gave photochemically prepared hydrogels upon dimerization of the anthracene groups via a [4+4] cycloaddition (Fig.…”

Aqueous Photon Upconversion by Anionic Acceptors Self-Assembled on Cationic Bilayer Membranes with a Long Triplet Lifetime

“…Triton X-100). 42 A relatively long triplet lifetime of 4.9 ms was observed in these quaternary biopolymer-surfactant donor-acceptor co-assembled gels; however, molecular-level information of those co-assembled structures in such a complex multicomponent mixture is difficult to obtain. Attaining a much longer triplet lifetime is essential to create superior TTA-UC systems that function under lower excitation light intensity, [11][12][13][14][15][16]27,28 while there is no rational means to prolong the triplet lifetimes in molecular selfassemblies.…”