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[Related articles/posters: 014 005 003 ] |
Peter
Koralla, Björn Åkermarka,
Per-Ola Norrbyb,*
a) Department of Chemistry, Organic
Chemistry, Royal Institute of Technology, S - 100 44 Stockholm, Sweden
b) Department of Medicinal Chemistry, Royal Danish School of Pharmacy, Universitetsparken 2, DK 2100 Copenhagen, Denmark
Abstract
Ru(II)-polypyridyl complexes are frequently
utilized as photosensitizers and photoelectron donors. This is due to a
unique combination of the chemical stability and the redox and excited
state properties of these complexes.1 Polypyridyl complexes
of Ru(II) have been used in a wide variety of applications. This includes
use as photosensitizers or photoelectron donors in diads and triads, and
for example use in metallodendrimers, use in chloride selective receptors,
and in rotaxanes. They have also been utilized in metal assisted self-assembly
of polypeptides and in DNA mediated electron transfer as DNA metallointercalators.
Several x-ray determinations of structures
have been reported for Ru(II)-polypyridine complexes. With this structural
data as a basis, together with a DFT frequency calculation on a smaller
model system, we have developed a molecular mechanics force field (MM3*).
This force field will allow extensive studies of new or existent, but less
thoroughly characterized, complexes.
Most photoinduced processes are strongly
distance dependent and most commonly also dependent on the geometries of
the photoactivated species. Comprehensive knowledge about geometries and
conformational energies will be of outmost importance in order to achieve
a better understanding of the photophysics and photochemistry of these
systems. This force field will hopefully lead to an improved design of
supramolecular devices and may also be utilized in combination with molecular
orbital calculations to predict properties of photosenitizers.
Conformationally flexible systems, composed
of photosensitizers covalently linked to electron donors or acceptors are
an important subject for this force field. Understanding the conformational
thermodynamics in these systems will be a valuable piece of information
in the analysis of the photochemistry. For an example see figure 1.
The parametrization have been performed
using automated routines recently developed.3 The parameter
refinement has been performed using various least-squares optimization
techniques, including Simplex and Newton-Raphson with numerically determined
derivatives, the latter allowing an accurate assessment of the convergence.
(See figure 2.) Two different types of substructure parameter sets have
been developed. The second set has an additional parameter, treating the
repulsive transeffect appearing in terpyidine complexes.
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1. Juris, A.; Balzani, V.; Barigelletti, F.; Campagna, S.;
Belser, P.; Von Zelewsky, A. Coord. Chem. Rev. 1988, 84, 85.
2. Sun, L.; Magnusson, A.; Berglund, H.; Korall, P.; Styring,
S.; Åkermark, B.; Hammarström, L. (to be submitted)
3. Norrby, P.-O.; Liljefors, T. submitted.
4. Ashby, M.T.;Govindan, G.N.; Grafton, A.K. Inorg.Chem.,
32, 3803,1993.