PROPERTIES AND REACTIONS OF CHARGE-TRANSFER EXCITED-STATES IN MONO-POLYNUCLEAR POLYPYRIDYL COMPLEXES OF RU, OS AND RE

Properties and reactions of different types of charge transfer excited states [metal-to-ligand (or MLCT), ligand-to-metal (or LMCT) and meta l-to-metal (MMCT)] of mono- and polynuclear polypyridyl complexes of R u, Os and Re are reviewed, with examples taken mostly from the work do ne in the authors' laboratory in the last decade. Properties and dynam ical aspects of the CT transitions are deduced from ground state absor ption, emission, transient absorption spectra, their lifetimes and aci d-base behaviour. Possible ways of tuning of the energy of the CT tran sitions art discussed followed by features of photoredox reactions. Po lynuclear complexes considered are bi- and trinuclear ones derived usi ng bis(2-pyridyl)pyrazine (dpp) or cyanide as the bridging ligand. Pro perties of mixed valence compounds formed during chemical oxidation or optical excitation are indicated and also intramolecular energy and e lectron transfer reactions involving central and peripheral chromophor es.