Transient resonance Raman investigation of excited states of [Rn(phen)(2)dppz](2+) and deuterated analogues in aqueous and non-aqueous environments

Transient resonance Raman (TR2) spectroscopy was used to investigate the co mplex [Ru(phen)(2)dppz](2+) (phen = 1,10-phenanthroline; dppz = dipyridophe nazine) following nanosecond pulsed laser excitation in three types of medi a: aqueous solution, DNA and acetonitrile. Studies were carried out at seve ral excitation wavelengths spanning the absorption range of the metal-ligan d charge-transfer (MLCT) excited state populated by the pulsed laser. In ad dition to the complex with the natural abundance dppz ligand, studies were also conducted with the complex containing the dppz ligand isotopically sub stituted at the phenanthroline hydrogens (i.e, d(6)-dppz). The intensity va riations observed for some of the prominent bands of the dppz(-.) radical a nion in the TR2 spectra as a function of excitation wavelength show that se veral distinct transitions contribute to the excited-state absorption. Whil e many of the bands observed can most readily be attributed to vibrations w hich involve the entire dppz ligand skeleton, the behaviour of a few featur es upon isotopic substitution suggests the involvement also of more confine d vibrational modes. The results of the transient resonance Raman studies a re discussed in the context of recent proposals concerning the nature of th e MLCT excited states possibly involved in the well-known use of the [Ru(ph en)(2)dppz](2+) complex as a 'light-switch reporter' for DNA, Copyright (C) 2000 John Whey & Sons, Ltd.