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 1H 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 in-creases in fluorescent intensity.These same isomers produced inclusion complexes with cucur-bit[8]uril which had moderate to fast exchange rates on the 1H 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 p-p stacked pairs which were cavity bound but also partly protruded from only one portal forming unsymmetrical host-guest complexes.In addition,these p-p stacked pairs formed orientation isomers within the confines of the cucur-bit[8]uril cavity.