a drop of ethanol into then-hexane was added to disassemble
the aggregates. The biexponential decays turned in a
monoexponential lifetime (Fig. 6).
The nature and the structure of such aggregates were also
investigated by means of dynamic light scattering and atomic
force microscopy.
We discussed how the numbers, size, and nature of the akyl
chain(s) can influence the formation of inverted vesicles or
micelles which could open new perspective toward the synthesis
of nanomaterials and, in particular, of photocatalysts. Multi-
chromophoric aggregates can also have an important role as
light-harvesting units or for the constitution of multicolor
emitting materials.
To exploit this last appealing possibility, we have investigated
energy transfer processes in self-assembled aggregates and, in
particular, in vesicles constituted of two different (in energy)
luminescent metallosurfactants ( 122 ). Both complexes
are charged and contain long chains dialkyl-bipyridine, as the
hydrophobic part of the structure. For the electronic energy,
acceptor and donor metallosurfactants bis(2,2^0 -bipyridine)(4,4^0 -
diheptadecyl-2,2^0 -bipyridine)ruthenium(II) dichloride (1) and bis
(4,6-difluorophenyl)pyridine
iridium(III) chloride ( 2 ) were chosen, respectively (Fig. 7).
The photophysical properties of these metallosurfactants,
namely 1 and 2 , were investigated in air-equilibrated aqueous
solution at room temperature, and the results compared with
the nonsurfactant analogues, namely, [Ru(bpy) 3 ]Cl 2 and
[Ir(dfppy) 2 (bpy)]Cl (where bpy¼2,2^0 -bipyridine and dfppy is 2,4-
difluorophenylpyridine). Also, the steady-state and time-resolved
emission properties of 1 and 2 were investigated in the presence
of a conventional cationic surfactant, as cetyltrimethylammonium
bromide (CTAB).
Below the CMC, both the compounds 1 and 2 showed
photophysical properties resembling their parental species with
a differentiated emission in the red region (lmax¼635 nm) for the
ruthenium complex and a green emission (lmax¼544 nm) for the
iridium compound. Both emissions display monoexponential
decays.
However, above the CMC, biexponential lifetime profiles and
enhanced emission quantum yields are observed for both
complexes. Comparison with the excited lifetime of the parental
complexes showed that the longer component can be assigned
to the aggregated species. Such findings could be explained in
terms of smaller nonradiative rate constant, as consequence of
64 CRISTIAN A. STRASSERTet al.