Photochemistry and Photophysics of Coordination Compounds
Photochemistry and Photophysics of Coordination Compounds
Photochemistry and Photophysics of Coordination Compounds
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Top Curr Chem (2007) 280: 215–255<br />
DOI 10.1007/128_2007_137<br />
© Springer-Verlag Berlin Heidelberg<br />
Published online: 27 June 2007<br />
<strong>Photochemistry</strong> <strong>and</strong> <strong>Photophysics</strong><br />
<strong>of</strong> <strong>Coordination</strong> <strong>Compounds</strong>: Rhodium<br />
Maria Teresa Indelli · Claudio Chiorboli · Franco Sc<strong>and</strong>ola (✉)<br />
Dipartimento di Chimica dell’Università, ISOF-CNR sezione di Ferrara, 44100 Ferrara,<br />
Italy<br />
snf@unife.it<br />
1 Introduction ................................... 216<br />
2 Mononuclear Species .............................. 218<br />
2.1 PolypyridineComplexes ............................ 218<br />
2.2 CyclometalatedComplexes ........................... 223<br />
3 Polynuclear <strong>and</strong> Supramolecular Species ................... 226<br />
3.1 HomobinuclearComplexes........................... 226<br />
3.2 Dyads....................................... 227<br />
3.2.1 Photoinduced Electron Transfer in Ru(II)-Rh(III) Polypyridine Dyads . . . 228<br />
3.2.2 Photoinduced Electron Transfer in Porphyrin-Rh(III) Conjugates . . . . . 234<br />
3.3 Triads<strong>and</strong>OtherComplexSystems ...................... 235<br />
3.4 PhotoinducedElectronCollection ....................... 239<br />
4 RhodiumComplexesasDNAIntercalators .................. 241<br />
4.1 SpecificBindingtoDNA<strong>and</strong>Photocleavage.................. 241<br />
4.2 Rh(III) Complexes in DNA-Mediated Long-Range Electron Transfer . . . . 245<br />
4.2.1 Rh(III) Complexes as Acceptors in Electron Transfer Reactions ....... 245<br />
4.2.2 Long Range Oxidative DNA Damage by Excited Rh(III) Complexes . . . . 248<br />
5 Conclusion .................................... 250<br />
References ....................................... 251<br />
Abstract Rhodium(III) polypyridine complexes <strong>and</strong> their cyclometalated analogues display<br />
photophysical properties <strong>of</strong> considerable interest, both from a fundamental viewpoint<br />
<strong>and</strong> in terms <strong>of</strong> the possible applications. In mononuclear polypyridine complexes,<br />
the photophysics <strong>and</strong> photochemistry are determined by the interplay between LC <strong>and</strong><br />
MC excited states, with relative energies depending critically on the metal coordination<br />
environment. In cyclometalated complexes, the covalent character <strong>of</strong> the C – Rh bonds<br />
makes the lowest excited state classification less clear cut, with strong mixing <strong>of</strong> LC,<br />
MLCT, <strong>and</strong> LLCT character being usually observed. In redox reactions, Rh(III) polypyridine<br />
units can behave as good electron acceptors <strong>and</strong> strong photo-oxidants. These<br />
properties are exploited in polynuclear complexes <strong>and</strong> supramolecular systems containing<br />
these units. In particular, Ru(II)-Rh(III) dyads have been actively investigated for the<br />
study <strong>of</strong> photoinduced electron transfer, with specific interest in driving force, distance,<br />
<strong>and</strong> bridging lig<strong>and</strong> effects. Among systems <strong>of</strong> higher nuclearity undergoing photoinduced<br />
electron transfer, <strong>of</strong> particular interest are polynuclear complexes where rhodium<br />
dihalo polypyridine units, thanks to their Rh(III)/Rh(I) redox behavior, can act as twoelectron<br />
storage components. A large amount <strong>of</strong> work has been devoted to the use <strong>of</strong>