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Photon upconversion is a process that combines low-energy photons to form useful high-energy photons. There are potential applications in photovoltaics, photocatalysis, biological imaging, etc. Semiconductor quantum dots (QDs) are promising for the absorption of these low-energy photons due to the high extinction coefficient of QDs, especially in the near infrared (NIR). This allows the intriguing use of diffuse light sources such as solar irradiation. In this review, we describe the development of this organic-QD upconversion platform based on triplet-triplet annihilation, focusing on the dark exciton in QDs with triplet character. Then we introduce the underlying energy transfer steps, starting from QD triplet photosensitization, triplet exciton transport, triplet-triplet annihilation, and ending with the upconverted emission. Design principles to improve the total upconversion efficiency are presented. We end with limitations in current reports and proposed future directions. This review provides a guide for designing efficient organic-QD upconversion platforms for future applications, including overcoming the Shockley-Queisser limit for more efficient solar energy conversion, NIR-based phototherapy, and diagnostics in vivo.
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Upconversion of Reductants
Abstract The many applications of photon upconversion—conversion of low‐energy photons into high‐energy photons—raises the question of the possibility of “electron upconversion”. In this Review, we illustrate how the reduction potential can be increased by using the free energy of exergonic chemical reactions. Electron (reductant) upconversion can produce up to 20–25 kcal mol−1of additional redox potential, thus creating powerful reductants under mild conditions. We will present the two common types of electron‐upconverting systems—dissociative (based on unimolecular fragmentations) and associative (based on the bimolecular formation of three‐electron bonds). The possible utility of reductant upconversion encompasses redox chain reactions in electrocatalytic processes, photoredox cascades, design of peroxide‐based medicines, firefly luminescence, and reductive repair of DNA photodamage.
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- Award ID(s):
- 1800329
- PAR ID:
- 10086327
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Angewandte Chemie International Edition
- Volume:
- 58
- Issue:
- 17
- ISSN:
- 1433-7851
- Format(s):
- Medium: X Size: p. 5532-5550
- Size(s):
- p. 5532-5550
- Sponsoring Org:
- National Science Foundation
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