4th EucheMs chemistry congress

tuesday, 28-Aug 2012
s738
chem. Listy 106, s587–s1425 (2012)
Nanochemistry / Nanotechnology / Molecular machines, Carbon tubes, sheets, balls
Molecular devices and machines – iii
o - 2 0 6
AnALoG And diGitAL ControL of MoLeCuLAr
funCtion By PhotoChroMeS
d. GuSt 1 , t. A. Moore 1 , A.L. Moore 1
1 Arizona State University, Department of Chemistry and
Biochemistry, Tempe Arizona, USA
Photochromes can interact with covalently linked
chromophores via energy or electron transfer and modification of
electronic coupling. Because these interactions are different for
the different isomers of the photochrome, these species may act
as digital switches to turn some properties of other chromophores
on or off. Molecules constructed in this way can perform logic
operations or other binary functions. The inputs and outputs of
these molecular devices can all be photonic, which avoids product
buildup, a need for physical access for reagents, and other
limitations inherent in the use of chemical inputs and outputs.
Such molecular digital devices may also be reconfigured to
perform other operations by changes in the wavelengths of the
inputs and outputs. For example, a molecule capable of carrying
out 13 different logic operations has been reported. In addition,
ensembles of photochromic molecules can carry out analog
control functions. In one example, a photochrome controls the
quantum yield of photoinduced electron transfer in an artificial
photosynthetic antenna-reaction center, thus mimicking a natural
photoprotective mechanism found in cyanobacteria. In another,
irradiation of a photochrome with modulated long-wavelength
light in turn modulates fluorescence of an attached chromophore
at a shorter wavelength. Such function could be useful in reducing
interference in fluorescent probe applications.
Keywords: Photochemistry; Photochromism; Molecular
devices;
Molecular devices and machines – iii
4 th EucheMs chemistry congress
o - 2 0 7
LiGht-hArveStinG AntennAe BASed on
LuMineSCent dendriMerS
P. Ceroni 1 , M. BAronCini 1 , G. BerGAMini 1 ,
e. MArChi 1
1 University of Bologna, Chemistry Ciamician, Bologna, Italy
Dendrimers are ideal candidates to build up molecular
antennae since a large number of different chromophoric units can
be arranged in a nanoobject with a predetermined pattern. Because
of their tree-like multi-branched structure, they can also form
internal dynamic cavities in which small molecules or ions can be
hosted, so that supramolecular structures can be self-assembled.
The value of the resulting supramolecular systems relies not only
on the total number of self-assembled molecules, but also on the
diversity of the components and on the functions resulting from
their mutual interactions.
In this view, we have studied self-assembled supramolecular
structures, based on dendrimers and metal
complexes [1] or molecular clips, which can perform also as
sensitizers of lanthanide ions. For example, we have
investigated several families of dendrimers containing a
1,4,8,11-tetraazacyclotetradecane (cyclam) core, [2] one of the most
extensively investigated ligands in coordination chemistry, to
build up metal complexes with dendritic ligands. [2] Particularly
interesting results have been obtained in the case of a dendrimer
constituted by two cyclam units linked by a photoswitchable
azobenzene chromophore and 12 naphthalene units at the
periphery. In this dendrimer, the distance between the two
cyclam units can be modulated by light stimuli thanks to the
presence of an azobenzene moiety which can be reversibly
switched between trans and cis isomer by light irradiation.
Therefore, the trans and cis isomers display different
coordination ability toward Zn(II) ion in CH CN:CH Cl 3 2 2
solution. Moreover, upon naphthalene excitation photosensitized
azobenzene isomerization takes place. To the best of our
knowledge, this represents the first example of a dendrimer
containing photochromic, luminescent and metal coordinating
units.
references:
1. C. Giansante, P. Ceroni, V. Balzani, F. Vögtle,
Angew. Chem. Int. Ed. 2008, 47, 5422.
2. G. Bergamini, E. Marchi, P. Ceroni, Coord. Chem. Rev.
2011, 255, 2458.
Keywords: photophysics; azobenzene; metal complex; energy
transfer; photoisomerization;
AUGUst 26–30, 2012, PrAGUE, cZEcH rEPUbLIc