Robust triplet–triplet annihilation photon upconversion by efficient oxygen scavenging

Abstract

We hereby present a simple method for reducing the effect of oxygen quenching in Triplet-Triplet Annihilation Upconversion (TTA-UC) systems. A number of commercially available thioethers and one thiol have been tested as singlet oxygen scavengers. Recording of the upconverted emission from a well-studied PdOEP (sensitizer)-DPA (annihilator/emitter) couple has been made over time with steady-state excitation capturing the steady-state kinetics of the TTA-UC process as the solubilized oxygen is depleted by reaction with the scavengers. The efficiency of the TTA-UC process is compared between chemical oxygen scavenging and mechanical removal by inert gas purging or the freeze-pump-thaw method. Selected methods are combined to explore the highest attainable TTA-UC quantum yield. A maximum TTA-UC quantum yield of 21% with the shortest UC onset time was obtained with dimethylthiomethane (DMTM) as the scavenger in an air-saturated solvent and slightly higher quantum yields were obtained in combination with other deoxygenation techniques. Samples containing DMTM displayed little decrease in the quantum yield over four hours of continuous high intensity irradiation, which illustrates the robustness of applying chemical oxygen removal in TTA-UC instead of more time-consuming mechanical processes that usually require specialized equipment.

Visible-to-ultraviolet (<340 nm) photon upconversion by triplet–triplet annihilation in solvents

“…2e were not considered to be governed by residual oxygen in the solvents, which was the case in previous visible-to-visible UC studies. [64][65][66][67][68] This is partly because the use of D-limonene, which scavenged residual oxygen efficiently and helped to attain stable visible-to-visible UC, 60 completely suppressed the UC emission in the present study. That the UC emission decays observed in Fig.…”

Green-to-Blue Triplet Fusion Upconversion Sensitized by Anisotropic CdSe Nanoplatelets

“…Reports by Castellano and others indicate that metal-organic complexes with strong spin-orbit coupling resulting from inclusion of heavy metal atoms can act as efficient triplet sensitizers for TTA-UC. 7,[14][15][16][17][18][19][20][21][22] While high UC efficiencies exceeding 20% have been reported in such systems, 23,24 one of the main limitations is the large energy gap between the singlet and the triplet state in these metal-organic complexes. As a result, over 300 meV energy losses can occur during the intersystem crossing (ISC) process required to create the triplet state.…”

Triplet-Triplet Annihilation PLGA-Nanoparticles for Cancer Bioimaging

“…Due to the high sensitivity of the porphyrin triplet states to oxygen quenching, the actual lifetime of the triplet state depends on the solvent, its purity and on its oxygen content 26 . To protect the optical properties of chromophores, PtOEP and DPA were dissolved in DCM.…”