Binding of rhodamine B and kiton red S to cucurbit[7]uril: density functional investigations

The binding of the laser dyes rhodamine B (RhB) and sulforhodamine B (kiton red S or KRS) to a cucurbit[7]uril (CB[7]) host has been investigated using density functional theory. Both guests (RhB and KRS) contain two N,N-diethylamino groups on a xanthene core. The lowest-energy structure of these host-guest complexes has one of the N,N-diethylamino groups encapsulated within the host cavity, that engenders C-H center dot center dot center dot O interactions with portals, while the remaining noninteracting diethylamino group resides outside the cavity. The H-1 NMR chemical shifts derived using the gauge-independent atomic orbital method are consistent with those observed in experiments.