Graduate Student Amanda Prascsak

"Efficiency of InP-Based Quantum Dots as Photocatalysts in Triplet-State Reactions"

Colloidal quantum dots (QDs) are particles, typically smaller than 5 nm, that are used as photocatalysts for organic reactions. These particles are exceedingly versatile. Despite their small overall size, QDs possess a large catalytic surface area. Therefore, they can support triplet-triplet energy transfer (TT EnT) by absorbing photons from the visible portion of the electromagnetic spectrum and passing that energy to the respective substrate or another co-catalyst. Moreover, this versatility is enhanced by their inherent dual nature. QDs have the electronic/optical tunability of homogeneous catalysts and the separation/surface templating ability of heterogeneous catalysts. Due to this range of advantageous properties, QDs make particularly effective photosensitizers while serving in their broader capacity as organic photocatalysts because they produce small singlet–triplet energy splitting, which leads to narrow emission line widths, and thus high photostability.1 Lead halide perovskite is one of the leading materials for these colloidal QDs because of its robust visible light absorption, high quantum yield (QY), and fair stability/recovery as a photosensitizer catalyst. However, an overarching problem with using Pb-based QDs is its innate toxicity that naturally raises the question of environmental hazards and their associated health risks. Nontoxic indium phosphide (InP) has been proposed as a “green” alternative to these QDs composed with lead or other heavy metals. InP-based QDs have shown to be rather effective photosensitizers, for they boast high efficiency and adequate photon upconversion quantum yields during triplet energy transfers.2 Hence, low-toxicity InP QDs can be harnessed to drive bright-state, thermally activated delayed photoluminescence (TADPL). Specifically, when InP QDs are functionalized with 8-quinolinecarboxylic acid (QCA), they demonstrate prolonged light emission in the blue region of the visible spectrum. The conjugation in the heterocyclic aromatic structure of QCA detours the triplet energy generated at the higher-lying bright state so that it avoids the electron trap states in InP QDs. The result is persistent light generation that can then be used to catalyze photochemical organic reactions more efficiently.3 This seminar will serve as a broad introduction to colloidal QDs, an exposition of “green” chemistry, for low-toxicity InP QDs will be compared with the traditional Pb QDs, and an exploration of application regarding the highly specialized role InP QDs play as photosensitizers in bright-state, TADPL triplet energy transfers.

References:
1. Jiang, Y.; Weiss, E. A. Colloidal Quantum Dots as Photocatalysts for Triplet Excited State Reactions of Organic Molecules. J. Am. Chem. Soc. 2020, 142 (36), 15219–15229. https://doi.org/10.1021/jacs.0c07421.
2. Lai, R.; Sang, Y.; Zhao, Y.; Wu, K. Triplet Sensitization and Photon Upconversion Using InP-Based Quantum Dots. J. Am. Chem. Soc. 2020, 142 (47), 19825–19829. https://doi.org/10.1021/jacs.0c09547.
3. Zhang, X.; Castellano, F. N. Thermally Activated Bright-State Delayed Blue Photoluminescence from InP Quantum Dots. J. Phys. Chem. Lett. 2022, 13 (16), 3706–3711. https://doi.org/10.1021/acs.jpclett.2c00582.