Despite most of the investigations on the ruthenium complexes
containing micelles deal with the quenching phenomena, there
are few papers in which the micelles have been used to enhance
the ruthenium emission ( 116 ). A protection from the environ-
ment and a reduction of the quenching by the dioxygen can be
achieved by shielding the metal complexes using dendritic
structures ( 118 ) and core/shell nanoparticles (119,120). Sauvage
and coworkers showed a different effect on investigating the
luminescence properties of Ru(bpy) 2 (ppz), namely, Ruppz,
where ppz¼dipyrido[3,2-a:2^0 ,3^0 -c]phenazine, in micellar SDS
solution. The complexRuppzdid not show any luminescence
in water, although it was a modest emitter in organic solvents
as ethanol. However, going from pure aqueous solution to a con-
dition in which the concentration of SDS is above its critical
micellar concentration (CMC), a dramatic enhancement of the
emission intensity was detected, the ratio being larger than a
factor of 3 ( 121 ). The quenching in such a case is not due to the
dioxygen but to the protonation of the pyrazine group in water
which turns off the emission.
Most of the micellar systems described so far are realized in
water. We recently reported on the aggregation features and
spectroscopic properties of inverted ruthenium bipyridyl
aggregates in low-polarity organic solvents( 116 ). Such systems
could help to further shed light on the role played by closely
organized metal centers. The design of molecules able to self-
organize in low-polarity solvents requires shrewd care, thus par-
ticular considerations have to be taken into account. Indeed, a
surfactant that could be able to aggregate into inverted micelles
has to match two different key aspects: a small head group and
voluminous hydrophobic substituents. As a result, a molecule
with a truncated cone architecture, where the head group
represents the narrow extreme of the cone, might be considered.
As far as a [Ru(bpy) 3 ]^2 þmoiety is concerned, the polar head
possesses a rather big volume of about 100 Å^2 , which requires
the hydrophobic tail to be voluminous enough to compensate
such a big head group. To reach this goal, we proposed
metallosurfactants containing from one to two and either linear
or branched alkyl chain substituted bipyridine, of general for-
mula [Ru(bpy) 3 n(bpyRx)n]Cl 2 withn¼1 or 2 and where bpyRx
stands for a 4,4^0 -dialkyl-2,2^0 -bipyridine ligand withxalkyl chains
(Fig. 6).
Due to the amphiphilic nature of the complex, inverted aggre-
gation in apolar organic solvents was realized, leading to the
formation or either inverted micelles or inverted vesicles.
62 CRISTIAN A. STRASSERTet al.