Ultrafast Photochemistry of the [Cr(NCS)₆]^3– Complex in Dimethyl Sulfoxide and Dimethylformamide upon Excitation into Ligand-Field Electronic State

Abstract

The ultrafast photochemistry of the [Cr­(NCS)6]3– complex upon excitation to the 4T2 ligand-field (LF) state was studied in dimethyl sulfoxide (DMSO) and N,N-dimethylformamide (DMF) in a wide temporal range (100 fs to 9 ms) by a combination of femtosecond and nanosecond transient absorption spectroscopy techniques and supported by quantum-chemical DFT/TD-DFT calculations. The initially excited 4T2 state undergoes intersystem crossing to the vibrationally hot 2E state with time constants of 1.1 ± 0.2 and 1.8 ± 0.1 ps in DMSO and DMF, respectively. Vibrational relaxation occurs in the same time scale and takes 1–5 ps. A major part of the [Cr­(NCS)6]3– complex in the 2E state undergoes intersystem crossing to the ground state with time constants of 65 ± 5 and 85 ± 5 ns in DMSO and DMF, respectively. A minor part of electronically excited [Cr­(NCS)6]3– undergoes irreversible photochemical decomposition. In DMSO, the photolysis of the [Cr­(NCS)6]3– complex results in single or double isothiocyanate ion release followed by the coordination of the solvent molecules with a time constant of 1 ± 0.2 ms.

Ultrafast Excited-State Dynamics of CuBr3–Complex Studied with Sub-20 fs Resolution

“…To quantify the VR and IC time constants, we analyzed the transient absorption peak integrated over the absorption band. The integrated transient absorption peak area as a function of delay time is expected to consist of the vibrational relaxation and the excited-state population decay components. ,− We integrated the Δ A spectra over the 660–930 nm absorption band (Figure ), and the resulting function was fitted by the double exponential decay: fast rise (τ 1 ) and the slow decay (τ 2 ); τ 1 = 27 ± 1 fs and τ 2 = 2.58 ± 0.02 ps for ACN and τ 1 = 37 ± 1 fs and τ 2 = 7.3 ± 0.2 ps for DCM. As mentioned above, the fast rise component τ 1 corresponds to the population rise of the LF state formed from the initially excited LMCT state.…”

“…The UV−vis spectra were measured using a Lambda 1050 (Perkin Elmer) UV−vis−NIR spectrophotometer. 34 We used a set of 0.1, 1, and 10 mm quartz cuvettes. All measurements were performed at room temperature, 21 °C.…”

High Surface Area of Polyhedral Chromia and Hexagonal Chromium Sulfide by the Thermolysis of Cyclohexylammonium Hexaisothiocyanatochromate(III) Sesquihydrate

“…4 T 1g (F) transition. [22,23,32,82,83,85,88,89] The UV-visible and FTIR absorbance spectra confirmed the binding of the thiocyanate ligand via its N-terminal to the Cr(III) ion centre.…”

Virtual Issue on Ultrafast Spectroscopy

“…19 Studies of the ultrafast to millisecond excited state evolution in [Cr(NCS) 6 ] 3− showed multiple pathways for relaxation and photochemistry. 20 simulations of ultrafast decay rate constants for Ru complexes were presented. It was shown how relaxing the assumption of sequential exponential decay can lead to new mechanistic information.…”

“…Ultrafast transient absorption (TA) of CuCl 4 2– revealed state dependent photochemistry, with a low lying ligand field energy level being photoinactive, while a higher energy LMCT state was dissociative . Studies of the ultrafast to millisecond excited state evolution in [Cr­(NCS) 6 ] 3– showed multiple pathways for relaxation and photochemistry . Kinetic simulations of ultrafast decay rate constants for Ru complexes were presented.…”