Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208-3113, United States.
J Am Chem Soc. 2022 Mar 9;144(9):3782-3786. doi: 10.1021/jacs.2c00833. Epub 2022 Mar 1.
Triplet excited state-initiated photochemistry is a mild and selective route to cycloadditions, radical rearrangements, couplings, fragmentations, and isomerizations. Colloidal quantum dots are proven visible-light photosensitizers and structural scaffolds for triplet-initiated reactions of molecules that are functionalized (with carboxylates) to anchor on the QD surface. Here, with the aid of polyaromatic energy shuttles that act as noncovalent adsorption sites for substrates on the QD surface, the scope of QD-photocatalyzed intermolecular [2 + 2] cycloadditions is extended to freely diffusing substrates (no anchoring groups). QD-shuttle complexes photocatalyze homo- and heterointermolecular [2 + 2] photocycloadditions of benzalacetone, chalcone and its derivatives with up to 94% yield; the yields for all reactions are comparable to those achieved by Ir(ppy) but with the advantages of a factor of 2.5 lower catalyst loading, superior stability, and the ability to recover the catalyst by simple centrifugation and reuse it for multiple reaction cycles. Experiments imply a two-step triplet-triplet energy transfer mechanism, one energy transfer from the QD to the energy shuttle followed by a second energy transfer from the shuttle to the transiently adsorbed substrate.
三重态激发态引发的光化学反应是一种温和且选择性的环加成、自由基重排、偶联、断裂和异构化方法。胶体量子点是可见光敏化剂和分子三重态引发反应的结构支架，这些分子经过（羧酸盐）官能化以锚定在 QD 表面上。在这里，借助多环芳烃能量穿梭物作为 QD 表面上底物的非共价吸附位点，扩展了 QD-光催化的分子间[2+2]环加成的范围，使其适用于自由扩散的底物（无锚固基团）。QD-穿梭复合物光催化苯甲醛、查尔酮及其衍生物的同分子和异分子[2+2]光环加成，产率高达 94%；所有反应的产率与 Ir(ppy)相当，但具有催化剂负载量低 2.5 倍、稳定性更好以及通过简单离心回收催化剂并可在多个反应循环中重复使用的优势。实验表明存在两步三重态-三重态能量转移机制，即从 QD 到能量穿梭物的能量转移，然后从穿梭物到瞬态吸附底物的第二次能量转移。
