Intra- and intermolecular vibrational energy transfer in tungsten carbonyl complexes W(CO)5(X) (X=CO, CS, CH3CN, and CD3CN)

Abstract

Vibrational energy relaxation of degenerate CO stretches of four tungsten carbonyl complexes, W(CO)6, W(CO)5(CS), W(CO)5(CH3CN), and W(CO)5(CD3CN), is observed in nine alkane solutions by subpicosecond time-resolved infrared (IR) pump-probe spectroscopy. Between 0 and 10 ps after the vibrational excitation, the bleaching signal of the ground-state IR absorption band shows anisotropy. Decay of the anisotropic component corresponds either to the rotational diffusion of the molecule or to the intramolecular vibrational energy transfer among the degenerate CO stretch modes. The time constant of the anisotropy decay, tauaniso, shows distinct solvent dependence. By comparing the results for the T1u CO stretch of W(CO)6 and the A1 CO stretch of W(CO)5(CS), the time constant of the rotational diffusion, taur, and the time constant of the intramolecular energy transfer among the three degenerate vibrational modes, taue, are determined as 12 and 8 ps, respectively. The tauaniso value increases as the number of carbon atoms in the alkane solvent increases. After 10 ps, the recovery of the bleaching becomes isotropic. The isotropic decay represents the vibrational population relaxation, from v=1 to v=0. In heptane, the time constant for the isotropic decay, tau1, for W(CO)5(CS) and W(CO)6 was 140 ps. The tau1 for the two acetonitrile-substituted complexes, however, shows a smaller value of 80 ps. The vibrational energy relaxation of W(CO)5(CH3CN) and W(CO)5(CD3CN) is accelerated by the intramolecular energy redistribution from the CO ligand to the acetonitrile ligand. In the nine alkane solutions, the tau1 value of W(CO)6 ranges between 124 and 158 ps, showing the apparent V-shaped solvent dependence with its minimum in decane, while the tau1 value shows little solvent dependence for W(CO)5(CH3CN) and W(CO)5(CD3CN).

Monitoring Photochemical Reaction Pathways of Tungsten Hexacarbonyl in Solution from Femtoseconds to Minutes

“…This decay component matches the average vibrational cooling time of ∼16 ps measured from time-resolved IR of the (CO) 5 W(NCCH 3 ) photoproduct. 37,48 The emerging negative signal is attributed to stimulated emission from the solvated [(CO) 5 W•••NCCH 3 ] complex, corroborated by previous reports of the ∼530 nm luminescence from W(CO) 5 coupled to a distinct nitrogen or other n-electron donors. 2,47 To reveal detailed structural dynamics during ultrafast photochemical reaction from a fresh perspective, we performed the excited state FSRS experiment 19,21,23 using a UV (267 nm) fs excitation pulse aiming to capture the transient Raman features in S 1 .…”

Vibrational Relaxation and Redistribution Dynamics in Ruthenium(II) Polypyridyl-Based Charge-Transfer Excited States: A Combined Ultrafast Electronic and Infrared Absorption Study

“…1,[6][7][8][9][10][11][12][13] Despite its important role in excited state dynamics, detailed investigations of vibrational relaxation dynamics in transition metal-based compounds are relatively limited in number. 3,[6][7][8][9]12,[14][15][16][17][18][19][20][21] In considering the general problem of understanding the mechanism of excited-state evolution in transition metal complexes, it occurred to us that an examination of this issue must confront two critical problems. First, the use of transient electronic absorption spectra to infer processes related to vibrational dynamics in transition metal-containing systems is a largely untested paradigm.…”

Ultrafast vibrational dynamics and solvation complexes of methyl acetate in methanol studied by sub‐picosecond infrared spectroscopy

“…Hamaguchi and coworkers have studied the solvent and the ligand dependences of the VER process of tungsten carbonyl complexes by IR pumpprobe spectroscopy. 15,16 In a series of IR pump-probe spectroscopic studies, we investigated the VER processes of the CO stretching modes of acetic acid in D 2 O 17 and 9-fluorenone (FL) in methanol. 18 When carbonyl compounds are dissolved into a protic solvent, intermolecular hydrogen bonds are formed between the oxygen atom of the carbonyl group and the hydroxyl group of the solvent molecules.…”