Time-resolved and steady-state luminescence and transient resonance Raman measurements have been carried out on the complex [Ru(phen) 2 dppz] 2+ (1) in the presence of single-stranded (ss) DNA that is either covalently attached to or mixed in 1:1 ratio with the complex. The well-known enhancement of luminescence (the "lightswitch" effect) exhibited by (1) when intercalated to double-stranded DNA is also observed in the presence of the single-stranded material, under conditions of covalent attachment or simple mixing. The evidence from both the luminescence and the transient Raman studies suggests that the enhancement need not necessarily reflect deep intercalation of the dppz ligand between the bases of the ss material.

The spin-crossover system [Fe(btpa)](PF(6))(2) (btpa = N,N,N',N'-tetrakis(2-pyridylmethyl)-6,6'-bis(aminomethyl)-2,2'-bipyridine) and the predominantly low-spin species [Fe(b(bdpa))](PF(6))(2) ((b(bdpa) = N,N'-bis(benzyl)-N,N'-bis(2-pyridylmethyl)-6,6'-bis(aminomethyl)-2,2'-bipyridine) have been characterized by means of X-ray diffraction. The unit cell of [Fe(btpa)](PF(6))(2) contains two crystallographically independent molecules revealing octahedral low-spin and quasi-seven-coordinated high-spin structures. The unit cell of [Fe(b(bdpa))](PF(6))(2) contains two crystallographically independent molecules one of which corresponds to a low-spin structure, while the other reveals a disordering. On the basis of magnetic susceptibility and Mössbauer measurements, it has been proposed that this disorder involves low-spin and high-spin six-coordinated molecules. The structures of [Zn(btpa)](PF(6))(2) and [Ru(btpa)](PF(6))(2) have been determined also. Pulsed laser photoperturbation, coupled here with time-resolved resonance Raman spectroscopy (TR(3)), has been used to investigate, for the first time by this technique, the relaxation dynamics in solution on nanosecond and picosecond time scales of low-spin, LS ((1)A) --> high-spin, HS ((5)T) electronic spin-state crossover in these Fe(II) complexes. For the nanosecond experiments, use of a probe wavelength at 321 nm, falling within the pi-pi transition of the polypyridyl backbone of the ligands, enabled the investigation of vibrational modes of both LS and HS isomers, through coupling to spin-state-dependent angle changes of the backbone. Supplementary investigations of the spin-crossover (SCO) equilibrium in homogeneous solution and in colloidal media assisted the assignment of prominent features in the Raman spectra of the LS and HS isomers. The relaxation data from the nanosecond studies confirm and extend earlier spectrophotometric findings, (Schenker, S.; Stein, P. C.; Wolny, J. A.; Brady, C.; McGarvey, J. J.; Toftlund, H.; Hauser, A. Inorg. Chem. 2001, 40, 134), pointing to biphasic spin-state relaxation in the case of [Fe(btpa)](PF(6))(2) but monophasic in the case of [Fe(b(bdpa))](PF(6))(2). The picosecond results suggest an early process complete in 20 ps or less, which is common to both complexes and possibly includes vibrational relaxation in the initially formed (5)T(2) state.

Detailed photophysical measurements on a series of [Ru(bpy)2(L)] n + complexes, which are deuterated to varying degrees are reported, where bpy is 2,2‘-bipyridyl and L is 3-(pyrazin-2-yl)-1,2,4- triazole (Hpztr) or 3-(pyridin-2-yl)-1,2,4-triazole (Hpytr). For the pyridinyltriazole complexes, deuteration of bpy leads to a doubling of the emission lifetime, while deuteration of the triazole ligand has no effect on the emission lifetime. For the complex containing the protonated pyrazinyltriazole ligand, deuteration of bpy does not affect the emission lifetime, but the lifetime is strongly affected by the deuteration of the triazole-containing ligand. These observations indicate that in the pyridinyltriazole complexes the emitting state is bpy based, while for the complex containing the protonated pyrazinyltriazole ligand the emission is pyrazine based. For the compound containing the deprotonated pyrazinyltriazole ligand a remarkable insensitivity of the emission lifetime to deuteration is observed. Time-resolved resonance Raman data clearly indicate that the emitting triplet state is bpy based at room temperature when the triazole is deprotonated and switches to being pyrazine based on protonation. Variable temperature emission studies on the deprotonated complex reveal a remarkable dual emission between 120 and 200 K. The two emitting states exhibit different lifetime dependences on temperature. It is proposed that the presence of these two, weakly coupled emitting states, one bpy and one pyrazine based, is responsible for the relative insensitivity of the emission lifetime of the deprotonated pyrazinyltriazole complex to deuteration.