Experimental assessment of the efficacy of sensitised emission in water from a europium ion, following intramolecular excitation by a phenanthridinylgroup

The overall quantum yields for phenanthridinium sensitised emission from a europium ion have been measured in H2O and D2O for a series of five structu rally related, octadentate ligands in which the distance from the phenanthr idinium chromophore to the Eu ion varies from 2.5 to ca. 8.2 Angstrom. Over all quantum yields (pD less than or equal to 2) range from 0.25 to 0.012 su ggesting that the experimental distance for 50% efficiency of intramolecula r energy transfer lies close to 5.5 Angstrom for this system.