SELF-ASSEMBLED HETERODINUCLEAR EUROPIUM(III)-LANTHANIDE(III) CHELATESOF N,N-BIS(CARBOXYMETHYL)AMINOMETHYL]-4-BENZOYLPHENOL AND THEIR RADIATIVE D-5(0)-]F-7(J) TRANSITIONS OF EU-III

A photochemical study has been conducted (i) to shed light on the intr amolecular T-1-relaxation pathways of N,N-bis(carboxymethyl)aminomethy l]-4-benzoylphenol (L) to initiate the radiative D-5(0) --> F-7(j) tra nsitions of Eu-III and (ii) to elucidate the effects of different aqua -bridged non-radiative Ln(III) cations on these Eu-III-specific radiat ive transitions, using the self-assembled heterodinuclear LEu(III)Ln(I II)L chelates where the Eu-III and Ln(III) cations are coordinated to each other by the aqua bridge inside the chelating cage consisting of two deprotonated phenolic hydroxy groups and four partially deprotonat ed 2,2'-(methylenenitrilo)bis(acetic acid) moieties. Depending on its non-radiative Ln(III) cation, the encapsulated aqua-bridged Eu(III)Ln( III) pair may be (i) as in the case of Ln(III) = Er-III, Ho-III, Nd-II I or Pr-III, a double-nuclear triplet relaxation centre where the T-1- relaxation occurs mainly to the excited state of Ln(III), (ii) as in t he case of Ln(III) = Gd-III or Y-III, a single-nuclear triplet relaxat ion centre where the T-1-relaxation is energetically capable of occurr ing only to the excited state D-5(j) of Eu-III, so that the resulting radiative D-5(0) --> F-7(j) transitions of Eu-III are to some extent e nhanced and, finally, (iii) as in the case of Ln(III) = Yb-III a singl e-nuclear triplet relaxation centre where the T-1-relaxation occurs on ly to the excited state of Eu-III, so that the resulting excited state of D-5(0) Eu-III is strongly destabilized by the aqua-bridged Yb-III: however, our present experimental results do not exclude the possibil ity of the aqua-bridged Yb-III cation occurring also as the T-1-relaxa tion centre despite the large energy gap Delta E(T-1 - F-2(7/2)) = 115 60 cm(-1).