TY - JOUR

T1 - Ultrafast Excited-State Dynamics of Ligand-Field and Ligand-to-Metal Charge-Transfer States of CuCl4 2- in Solution

T2 - A Detailed Transient Absorption Study

AU - Mereshchenko, Andrey S.

AU - Myasnikova, Olesya S.

AU - Olshin, Pavel K.

AU - Matveev, Sergey M.

AU - Panov, Maxim S.

AU - Kochemirovsky, Vladimir A.

AU - Skripkin, Mikhail Yu

AU - Tarnovsky, Alexander N.

PY - 2018/11/22

Y1 - 2018/11/22

N2 - Ultrafast excited-state dynamics of CuCl4 2- in acetonitrile is studied by femtosecond broadband transient absorption spectroscopy following excitation of the complex into all ligand-field (LF or d-d) states and into the two ligand-to-metal charge transfer (LMCT) states corresponding to the most intense steady-state absorption bands. The LF excited states are found to be nonreactive. The lowest-lying 2E LF excited state has a lifetime less than 150 fs, and the lifetimes of the second (2B1) and the third (2A1) LF excited states are 1 and 5 ps, respectively. All three LF states decay directly into the ground 2B2 state. Such significant differences in excited-state decay time constants were rationalized computationally through time-dependent density functional theory (TD-DFT) computations. TD-DFT mapping of the relaxation pathway along the symmetric Cl-Cu-Cl umbrella bending vibration gives evidence for a conical intersection between the 2E excited state and the ground 2B2 state. The LMCT states decay within 200 fs with the primary deactivation mode consistent to be Cu-Cl stretch. A fraction of the CuCl4 2- complexes excited into the LMCT states undergoes ionic dissociation to form products that survive longer than 1 ns. The remaining fraction undergoes internal conversion, which can be viewed as back electron transfer, populating the lower vibrationally hot LF states. The LF states populated from the LMCT states exhibit the same lifetimes as the Franck-Condon LF states and likewise decay directly into the ground state.

AB - Ultrafast excited-state dynamics of CuCl4 2- in acetonitrile is studied by femtosecond broadband transient absorption spectroscopy following excitation of the complex into all ligand-field (LF or d-d) states and into the two ligand-to-metal charge transfer (LMCT) states corresponding to the most intense steady-state absorption bands. The LF excited states are found to be nonreactive. The lowest-lying 2E LF excited state has a lifetime less than 150 fs, and the lifetimes of the second (2B1) and the third (2A1) LF excited states are 1 and 5 ps, respectively. All three LF states decay directly into the ground 2B2 state. Such significant differences in excited-state decay time constants were rationalized computationally through time-dependent density functional theory (TD-DFT) computations. TD-DFT mapping of the relaxation pathway along the symmetric Cl-Cu-Cl umbrella bending vibration gives evidence for a conical intersection between the 2E excited state and the ground 2B2 state. The LMCT states decay within 200 fs with the primary deactivation mode consistent to be Cu-Cl stretch. A fraction of the CuCl4 2- complexes excited into the LMCT states undergoes ionic dissociation to form products that survive longer than 1 ns. The remaining fraction undergoes internal conversion, which can be viewed as back electron transfer, populating the lower vibrationally hot LF states. The LF states populated from the LMCT states exhibit the same lifetimes as the Franck-Condon LF states and likewise decay directly into the ground state.

KW - COPPER(II) CHLORO COMPLEXES

KW - PUMP-PROBE

KW - FEMTOSECOND SPECTROSCOPY

KW - COOLING DYNAMICS

KW - SOLVENT EXCHANGE

KW - WILSONS-DISEASE

KW - PHOTOCHEMISTRY

KW - ACETONITRILE

KW - SPECTRA

KW - PHOTOLYSIS

UR - http://www.scopus.com/inward/record.url?scp=85056801904&partnerID=8YFLogxK

U2 - 10.1021/acs.jpcb.8b06901

DO - 10.1021/acs.jpcb.8b06901

M3 - Article

C2 - 30375871

AN - SCOPUS:85056801904

VL - 122

SP - 10558

EP - 10571

JO - Journal of Physical Chemistry B

JF - Journal of Physical Chemistry B

SN - 1520-6106

IS - 46

ER -