A cucurbit[8]uril-mediated host–guest complex for red-light photocatalysis

A red-light supramolecular photocatalytic system was developed by fabricating a cucurbit[8]uril-mediated 3 : 2 host–guest complex. Two-step host–guest complexation occurs between 4,4′-(thiazolo[5,4-d]thiazole-2,5-diyl) bis(6-(pyrrolidin-1-yl)-[1,3-bipyridin]-1-ium) chloride (TPP), an elongated molecule, and cucurbit[8]uril (CB[8]), leading to the formation of two host–guest complexes, namely CB[8]@2TPP and 3CB[8]@2TPP, sequentially. The formation of CB[8]@2TPP and then 3CB[8]@2TPP was indicated to lead to a continuously enhanced intermolecular interaction between TPPs, with 3CB[8]@2TPP eventually exhibiting a considerable ability to absorb red light and a long-lived triplet state. In addition, the electron transfer as well as energy transfer between 3CB[8]@2TPP and oxygen were determined to proceed smoothly. As a result, 3CB[8]@2TPP can serve as an efficient red-light photocatalyst for the oxidation of boronic acids.