Picosecond TR~3 examination of the 'light-switch' states of Ru(phen)_2dppz~(2+)

摘要

Ru(II) and Os(II) complexes with the planar aromatic ligand, dipyridophenazine (dppz), have been the subject of continuing interest, primarily due to potentially useful photophysical/redox perturbations induced by interaction with nucleic acids. The complex [Ru(phen)_2dppz]~(2+) (1) has been studied extensively, with particular interest in the 'light switch effect' exhibited by the complex in which the characteristically weak emission from the MLCT excited state in aqueous soltuion is greatly enhanced upon interaction with DNA. Emphasis has been placed on probing of the complex in solvent environments of varying polarity and hydrogen bonding ability in order to try to characterise this interesting photophysics. A mechanism for the effect has been proposed, involving interaction between two MLCT states which differ markedly in the rate of solvent-dependent radiationless decay. The use of time-resolved vibrational spectroscopy as a probe of the low-lying excited states of transition metal complexes is well recognised.