Host-guest complexes of cucubit[8]uril with phenanthrolines and some methyl derivatives

The host-guest relationship between cucurbit[8]uril, phenanthrolines and some methyl substituted 1,10-phenanthrolines has been investigated by using H-1 NMR spectroscopy and fluorescence spectroscopy. The results showed that phenanthrolines as molecular guests bind in the cavity and portal of cucurbit[8]uril in a ratio of 2: 1 (guest to host). The phenanthroline isomers 1,10-,1,7- and 4,7- showed red shifts between 47 and 108 nm and pronounced increases in fluorescent intensity. These same isomers produced inclusion complexes with cucurbit[8]uril which had moderate to fast exchange rates on the H-1 NMR time scale. The methyl substituted 1,10-phenanthrolines studied gave stable inclusion complexes in a ratio of 2:1 which showed slow exchange rates. These guests formed pi-pi stacked pairs which were cavity bound but also partly protruded from only one portal forming unsymmetrical host-guest complexes. In addition, these pi-pi stacked pairs formed orientation isomers within the confines of the cucurbit[8]uril cavity.