Applications and Prospects for Triplet-Triplet Annihilation Photon Upconversion

Abstract

Triplet-triplet annihilation photon upconversion (TTA-UC) is a photophysical process in which the energy of two photons are combined into a single photon of higher energy. While this strategy has been recognized in applications ranging from bioimaging to solar energy conversion, its uses in synthetic organic chemistry have not been extensively developed. Here, we present a short tutorial on the theoretical underpinnings and the design principles of TTA-UC systems. Selected applications are then discussed to highlight key features of the TTA mechanism, along with a prospective discussion of the potential of these mechanisms to enable innovation in photocatalysis, methods development, and synthetic organic chemistry.

Fig. 1.

Energy diagram illustrating the mechanism of TTA-UC as described in the text.

Fig. 2.

In vivo bioimaging using TTA-UC nanocapsules in the liver 1 of a mouse compared to its spleen 2 and the ex vivo kidney 3. Reprinted (adapted) with permission from Liu, Q., Xu, M., Yang, T., Tian, B., Zhang, X., Li, F., ACS Appl. Mater. Interfaces 2018, 10, 9883. Copyright 2018 American Chemical Society.

Fig. 3.

TTA-UC followed by FRET to promote photodissocation of Ru prodrugs. P - perylene

Fig. 4.

Cell-targeting nanoparticles activated through TTA-UC. Reprinted (adapted) with permission from Wang, W., Liu, Q., Zhan, C., Barhoumi, A., Yang, T., Wylie, R., Armstrong, P., Kohane, D., Nano Lett. 2015, 15, 6332. Copyright 2015 American Chemical Society.

Fig. 5.

Hydroxyl radical formation with sub-bang-gap photons.

Fig. 6.

Photodeformable films activated by red light through TTA-UC. Reprinted (adapted) with permission from Jiang, Z., Xu, M., Li, F., Yu, Y., J. Am. Chem. Soc. 2013, 135, 16446. Copyright 2013 American Chemical Society.

Fig. 7.

Proposed catalytic cycle for photoreduction of aryl halides.

Fig. 8.

Substrate scope of intragel photoreduction of aryl halides.

Fig. 9.

Catalytic cycle propsed by König for the sensitization-induced electron transfer reaction.