Inclusion Complexes of Styryl Dyes with Cucurbiturils: Ultrafast Relaxation of Electronically Excited States

Published data on the ultrafast (in the picosecond range) relaxation of electronically excited inclusion complexes between macrocyclic cavitands consisting of n glycoluril units (n = 5–8), cucurbit[n]urils (CB[n]), and styryl dyes are considered. The relaxation process is accompanied by the translational movement of the dye cation deep into the cavity of cucurbiturils. In the 1 : 1 complexes with CB[6], this movement occurs along the central axis of the cavitand with a characteristic time of 1–2 ps at room temperature. By definition, such supramolecular systems are called molecular machines. In supramolecular 2 : 1 complexes with CB[8], the [2 + 2] photocycloaddition reaction of styryl dyes is possible. A physically clear model of the movement of electronically excited dye cations in the cavity of cucurbiturils is considered, which gives an estimate of the characteristic operating time of the molecular machine that is in good agreement with the experiment.