Raman probing of excited states of the tris(2,2′-bipyridine)Cr(III) complex having lifetimes in the micro-and picosecond regions

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Abstract
Population and Raman scattering of the 2E and 4T2 electronic excited states with lifetimes of τE?60 μs and τT?10 ps of the complex tris(2,2′‐bipyridine)Cr(III) is achieved by exposing the complex Cr(bpy)3 (ClO4)3 in H2O to radiation at 457.9 nm from tunable pulsed and cw fixed wavelength lasers. The spectra for 2E and ground state Cr(bpy)33+ are very similar but differences of intensities, FWHM and shifts of corresponding vibrational Raman bands of 4T2 and 4A2:Cr(bpy)3+ are more pronounced. The differences in FWHM are attributed to the contribution to the overall Raman intensity for the former of vibrational scattering in vibrational states in the top as well as in the bottom of the 4T2 electronic surface of some of the modes of the complex. This because the wavelength of the pumping source is in resonance with vibrational states in the top of that surface and the cascading process reveals itself in the time resolved Raman studies at the nanosecond level.