Expected and unexpected photoreactions of 9-(10-)substituted anthracene derivatives in cucurbit[n]uril hosts

By arranging substrates in a “reaction ready” state through noncovalent interactions, supramolecular nanoreactors/catalysts show high selectivity and/or rate acceleration features. Herein, we report the host–guest complexation of 9-(10-)substituted anthracene derivatives (G1–G3) with cucurbitn]uril (CBn], n = 8, 10), and the photoreactions of these derivatives in the presence of CBn] hosts. Both CB10] and CB8] showed no obvious effects on the photoreaction of 9,10-disubstituted derivative G1. For G2 and G3, CB10] operated as either a nanoreactor or catalyst (10%) for the photodimerization of two compounds with high selectivity and high yield. However, although CB8] formed a 1 : 2 complex with G2, as also observed with CB10], the photosolvolysis product (9-anthracenemethanol) was obtained quantitatively after photoirradiation of the CB8]·2G2 complex. This unexpected photosolvolysis was rationalized by a plausible catalytic cycle in which anthracene acts as a photoremovable protecting group (PPG) and the carbonium ion intermediate is stabilized by CB8].

The photodimerization of 9-substituted anthracene derivative was tremendously promoted by a catalytic amount of cucurbit10]uril (CB10]) in water. While CB8] exclusively induced the photosolvolysis of the anthracene derivative.