The complexes [Eu(bpcd)(tta)],
[Eu(bpcd)(Coum)], and [Tb(bpcd)(Coum)]
[tta = 2-thenoyltrifluoroacetyl-acetonate, Coum = 3-acetyl-4-hydroxy-coumarin,
and bpcd =N,N′-bis(2-pyridylmethyl)-trans-1,2-diaminocyclohexane-N,N′-diacetate] have been synthesized and characterized
from photophysical and thermodynamic points of view. The optical and
chiroptical properties of these complexes, such as the total luminescence,
decay curves of the Ln(III) luminescence, electronic circular dichroism,
and circularly polarized luminescence, have been investigated. Interestingly,
the number of coordinated solvent (methanol) molecules is sensitive
to the nature of the metal ion. This number, estimated by spectroscopy,
is >1 for Eu(III)-based complexes and <1 for Tb(III)-based complexes.
A possible explanation for this behavior is provided via the study
of the minimum energy structure obtained by density functional theory
(DFT) calculations on the model complexes of the diamagnetic Y(III)
and La(III) counterparts [Y(bpcd)(tta)], [Y(bpcd)(Coum)], and [La(bpcd)(Coum)].
By time-dependent DFT calculations, estimation of donor–acceptor
(D–A) distances and of the energy position of the S1and T1ligand excited states involved in theantennaeffect was possible. These data are useful for rationalizing
the different sensitization efficiencies (ηsens)
of theantennaetoward Eu(III) and Tb(III). The tta
ligand is an optimalantennafor sensitizing Eu(III)
luminescence, while the Coum ligand sensitizes better Tb(III) luminescence
{ϕovl= 55%; ηsens≥ 55%
for the [Tb(bpcd)(Coum)] complex}. Finally, for the [Eu(bpcd)(tta)]
complex, a sizable value ofglum(0.26)
and a good quantum yield (26%) were measured.