Conférences de :
- Arthur CAMMERS (Université du Kentucky, Lexington, USA) le
jeudi 30 avril 2009 à 16 h : «
Unveiling weak molecular interactions : the secret lives of
molecules ».
- Paola CERONI (Université de Bologne, Italie) le
jeudi 7 mai 2009 à 16 h : «
Dendrimers as new optoelectronic materials ».
Lieu : CINaM (salle Raymon Kern), Campus de Luminy, Marseille.
Résumé : Arthur CAMMERS
Aspects of canonical molecular interactions will be discussed.
Pi-stacking, crystal packing and hydrogen bonding have been the
subjects of many papers in the chemical literature, but how do
these weak interactions impact and relate to dynamic conformations
of organic molecules in solution? A few examples from our work will
be presented.
Résumé : Paola CERONI
Dendrimers are highly branched tree-like macromolecules with
well-defined composition and a high degree of order. They usually
consist of a core upon which radially branched layers are
covalently attached. By using suitable synthetic strategies it is
possible to prepare dendrimers that contain selected functional
units in predetermined sites of their structure. Such compounds can
often exhibit remarkable chemical, physical and biological
properties, with a wide range of potential applications in
different fields such as medicine, biology, chemistry, physics, and
engineering. Because of their tree-like multi-branched structure,
dendrimers can also form internal dynamic cavities in which small
molecules or ions can be hosted. In this view, we have studied
self-assembled supramolecular structures based on dendrimers that
can perform as light-harvesting antenna. For example, dendrimer D,
consisting of a 1,4,8,11 - tetraazacyclotetradecane (cyclam) core
with appended 12 dimethoxybenzene and 16 naphthyl units is able to
form a self-assembled structure in a CH3CN:CH2Cl2 solution
containing a metal complex, namely [Ru(bpy)2(CN)2] in a 1:1 molar
ratio, and Nd(III) ions. In the three-component system,
{D•Nd(III)•[Ru(bpy)2(CN)2]}, dendrimer D and the Ru(II)
complex play the role of ligands for Nd(III). Because of the
complementary properties of the three components, new functions
emerge from their assembly. Such a system behaves as an antenna
that can harvest UV to VIS light absorbed by both the dendrimer and
the Ru(II) complex and emit in the NIR region with line-like bands
and long excited state lifetime, typical of the Nd(III) ion. In
principle, the emission wavelength can be tuned by replacing
Nd(III) with other lanthanide ions possessing low-lying excited
states. Useful applications can be envisaged in the field of
imaging, and solar cells. Another interesting example is
constituted by a family of polysulfurated pyrene-cored dendrimers
that exhibit remarkable photophysical and redox properties : a
strong core-localized fluorescence band (λmax = 460 nm,
Φ = 0.6, τ = 2.5 ns), a stable and deep-blue radical
cation. The strong blue fluorescence and the yellow to deep-blue
color change upon reversible one electron oxidation might be
exploited for optoelectronic and electrochromic applications.