Spectra and Relaxation Dynamics of the Pseudohalide (PS) Vibrational Bands for Ru(bpy)2(PS)2 Complexes, PS = CN, NCS and N3

Published

December 5, 2012

Author(s)

Edwin J. Heilweil, Ryan Compton, Helen K. Gerardi, Daniel Weidinger, Douglas J. Brown, Walter J. Dressick, Jeffrey C. Owrutsky

Abstract

The RuII cyclometalated dye complex, cis-Ru(bpy)2(N3)2 (where bpy = 2,2’-bipyridine), along with two more familiar analogs with pseudohalide (PS) ligands, cis-Ru(bpy)2(NCS)2 and cis-Ru(bpy)2(CN)2, were investigated in solution with static and transient infrared spectroscopy. The CN stretching IR band for cis-Ru(bpy)2(NCS)2 appears at higher frequency (near 2106 cm-1 in dimethyl sulfoxide, DMSO) than for the free NCS- anion (which is centered near 2066 cm-1 in the gas phase and dissolved in polar solvents). However, the bands for the PS = N3 (2027 cm−1) and cyanide (2068 cm−1) complexes are closer to that of the respective free anion. The metal-to-ligand charge transfer (MLCT) band observed in the UV – Visible spectrum is shifted to longer wavelengths for the cis-Ru(bpy)2(N3)2 species (565 nm) compared to the analogous PS = NCS (511 nm) and PS = CN (502 nm) complexes. Infrared pump – infrared probe transient spectroscopy results show that the vibrational energy relaxation (VER) lifetime for the PS = N3 complex is an order of magnitude shorter (~ 5 ps) than for either the PS = NCS or PS = CN species (which are both near 70 ps in DMSO). The VER times of the complexes are similar to those for each corresponding free anion in moderately interacting solvents (e.g., DMSO). However, there is more of a solvent dependence for the cis-Ru(bpy)2(N3)2 vibrational band frequency than for its lifetime, which suggests that intramolecular vibrational relaxation (IVR) is predominant over solvent energy-extracting interactions. The results are also compared to other similar metal complexes in solution.

Citation

Chemical Physics

Volume

422

Pub Type

Journals

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DOI Link

Keywords

Ruthenium complexes, vibrational relaxation dynamics, pseudohalide ligands, energy transfer, sensitizer dyes, solar energy, relaxation mechanisms

Citation

Heilweil, E. , Compton, R. , Gerardi, H. , Weidinger, D. , Brown, D. , Dressick, W. and Owrutsky, J. (2012), Spectra and Relaxation Dynamics of the Pseudohalide (PS) Vibrational Bands for Ru(bpy)2(PS)2 Complexes, PS = CN, NCS and N3, Chemical Physics, [online], https://doi.org/10.1016/j.chemphys.2012.11.015 (Accessed October 12, 2024)