Supramolecular photocatalysis by confinement--photodimerization of coumarins within cucurbit[8]urils.

Cucurbit[8]uril (as low as 10 mol%) acts as a supramolecular catalytic nanoreaction vessel and facilitates the photodimerization of coumarins in water leading to syn dimers. Saturation kinetics shows a sigmoidal dependence with a turnover number of 3.4 min(-1) and a Hill constant of 1.8 indicating a co-operative mechanism in the catalytic process.