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

Ultrafast excited-state dynamics of CuBr3- complex was studied in acetonitrile and dichloromethane solutions using femtosecond transient absorption spectroscopy with 18 fs temporal resolution and quantum-chemical DFT calculations. Upon 640 nm excitation, the CuBr3- complex is promoted to the ligand-to-metal charge transfer (LMCT) state, which then shortly undergoes internal conversion into the vibrationally hot ligand field (LF) excited state with time constants of 30 and 40 fs in acetonitrile and dichloromethane, respectively. The LF state nonradiatively relaxes into the ground state in 2.6 and 7.3 ps in acetonitrile and dichloromethane, respectively. Internal conversion of the LF state is accompanied by vibrational relaxation that occurs on the same time scale. Based on the analysis of coherent oscillations and quantum-chemical calculations, the predominant forms of the CuBr3- complex in acetonitrile and dichloromethane solutions were revealed. In acetonitrile, the CuBr3- complex exists as [CuBr3 (CH3CN)(2)(-)], whereas three forms of this complex, [CuBr3CH2 Cl-2](-), [CuBr3(CH2Cl2)(2)](-), and CuBr3(CH2Cl2)(3)](-), are present in equilibrium in dichloromethane.

Automated summary

Ultrafast excited-state dynamics of CuBr3- complex in acetonitrile and dichloromethane solutions show rapid internal conversion from LMCT to LF state, followed by nonradiative relaxation back to the ground state with vibrational relaxation. Different predominant forms of CuBr3- complex were observed in acetonitrile ([CuBr3(CH3CN)2]-) and dichloromethane ([CuBr3CH2Cl2]-, [CuBr3(CH2Cl2)2]-, [CuBr3(CH2Cl2)3]-).