synthesis of ruthenium(52,100,101), rhenium- ( 102 ), and iron-
based amphiphiles ( 103 ). Further, Bruceet al. have correlated
the shape and chemical nature of the ligand coordinated to the
ruthenium ion with the resulting structure of the aggregates.
Ruthenium metallosurfactants as the polar head group, which
contains a single alkylated bipyridine as hydrophobic part,
namely, [Ru(bpy) 2 (R 2 -bpy)]^2 þ, have been also investigated
(50,51,100,104). Even though these aggregates are potentially
luminescent, particularly, ruthenium(II) complexes incorporating
bipyridyl units stand out for their robustness, reactivity, as well as
rich electro- and photochemical properties (105,106), no informa-
tion on the variation of the photophysical properties were reported
for most of the systems.
Going from small molecules to macromolecules-based systems
and taking advantage from the well-known tendency of amphi-
philic block copolymers to aggregate in micelles in aqueous media,
Gohy and coworkers showed the possibility to aggregate metal-
losupramolecular amphiphilic block copolymers consisting of a
core formed by hydrophobic and insoluble poly(styrene) (PS) or
poly(ethylene-co-butylene) (PEB) blocks, surrounded by a hydro-
philic poly(ethylene oxide) (PEO). These two blocks are held
together by bis-2,2^0 :6^0 ,2^00 -terpyridine-ruthenium moieties, namely,
[Ru(R^0 -tpy)(R^00 -tpy)], which are thought located at the corona
core-corona interface( 107 – 110 ). The metallosupramolecular block
copolymer micelles have been recently reviewed by Gohy; thus no
more room will be dedicated to this topic hereafter ( 111 ).
However, Sleiman and coworkers investigated the synthesis of
homopolymers block copolymers containing dense arrangement
of ruthenium bipyridyl complexes by using ring-opening metath-
esis polymerization (ROMP). In this case, the hydrophobic poly-
meric tails face the solvent and act as protecting shield for the
polar head, while the core of these aggregates is expected to be
formed by the ruthenium moieties. Thus, the block copolymers
organized in such a way that the ruthenium moieties displayed
a lack of interchromophore interactions with consequent preser-
vation of the redox and photophysical properties(112,113).
As already mentioned, to rationalize the shape and size of the
aggregate is difficult and also the number of studies on the rela-
tionship between structure and the physicochemical properties of
these luminescent metalloaggregates remain limited so far
(50,104,114,115), and mostly dealing with spherical micelles,
even though few vesicular systems have been also reported ( 116 ).
In addition, these aggregates have been studied mainly in aqueous
solutions, while there are only few known metallosurfactants
which aggregate in organic solvents (116,117).
PHOTOPHYSICS OF MOLECULAR ASSEMBLIES 61