Excited state dynamics and activation parameters of remarkably slow photoinduced CO loss from (η6-Benzene)Cr(CO)3 in n-heptane solution: A DFT and picosecond-time-resolved infrared study

Ian P. Clark; Michael W. George; Gregory M. Greetham; Emma C. Harvey; Conor Long; Jennifer C. Manton; Mary T. Pryce

doi:10.1021/jp106290j

Excited state dynamics and activation parameters of remarkably slow photoinduced CO loss from (η⁶-Benzene)Cr(CO)₃ in n-heptane solution: A DFT and picosecond-time-resolved infrared study

Ian P. Clark, Michael W. George, Gregory M. Greetham, Emma C. Harvey, Conor Long, Jennifer C. Manton, Mary T. Pryce

Research output: Journal Publication › Article › peer-review

17 Citations (Scopus)

Abstract

The electronic structure of (η⁶-benzene)Cr(CO)₃ has been calculated using density functional theory and a molecular orbital interaction diagram constructed based on the Cr(CO)₃ and benzene fragments. The highest occupied molecular orbitals are mainly metal based. The nature of the lowest energy excited states were determined by time-dependent density functional theory, and the lowest energy excited state was found to have significant metal to carbonyl charge transfer character. The photochemistry of (η⁶-benzene)Cr(CO)₃ was investigated by time-resolved infrared spectroscopy with picosecond time resolution. The low energy excited state was detected following irradiation at 400 nm, and this exhibited _CO bands at lower energy than the equivalent _CO bands of (η⁶-benzene)Cr(CO)₃, consistent with metal to carbonyl charge transfer character, and is formed with excess vibrational energy, relaxing to the v = 0 vibrational state within 3 ps. The resulting "cold" excited state decays to form the CO-loss species (η⁶-benzene)Cr(CO)₂ in approximately 70% yield and to reform (η⁶-benzene)Cr(CO)₃ within 150 ps. The rates of relaxation from the vibrationally hot state to the cold excited state and its subsequent reaction to yield (η⁶-benzene)Cr(CO)₂ were measured over a range of temperatures from 274 to 320 K, and the activation parameters for both processes were obtained from Eyring plots. The vibrational relaxation exhibits a negative activation enthalpy ΔH^‡ (-10 (±4) kJ mol^-1) and a negative activation entropy ΔS^‡ (-50 (±16) J mol^-1 K ^-1). A significant barrier (ΔH^‡ = +12 (±4) kJ mol^-1) was obtained for the formation of (η⁶-benzene)Cr(CO)₂ with a ΔS^‡ value close to zero. These data are used to propose a model for the CO-loss process to yield (η⁶-benzene)Cr(CO)₂ and to explain why low temperature irradiation of (η⁶-benzene)Cr(CO)₃ with light of wavelengths greater than 400 nm produced relatively minor amounts of (η⁶-benzene)Cr(CO)₂.

Original language	English
Pages (from-to)	11425-11431
Number of pages	7
Journal	Journal of Physical Chemistry A
Volume	114
Issue number	43
DOIs	https://doi.org/10.1021/jp106290j
Publication status	Published - 4 Nov 2010
Externally published	Yes

ASJC Scopus subject areas

Physical and Theoretical Chemistry

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10.1021/jp106290j

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Clark, I. P., George, M. W., Greetham, G. M., Harvey, E. C., Long, C., Manton, J. C., & Pryce, M. T. (2010). Excited state dynamics and activation parameters of remarkably slow photoinduced CO loss from (η⁶-Benzene)Cr(CO)₃ in n-heptane solution: A DFT and picosecond-time-resolved infrared study. Journal of Physical Chemistry A, 114(43), 11425-11431. https://doi.org/10.1021/jp106290j

@article{18c12d473b6b49ca9a3a6763930cee33,

title = "Excited state dynamics and activation parameters of remarkably slow photoinduced CO loss from (η6-Benzene)Cr(CO)3 in n-heptane solution: A DFT and picosecond-time-resolved infrared study",

abstract = "The electronic structure of (η6-benzene)Cr(CO)3 has been calculated using density functional theory and a molecular orbital interaction diagram constructed based on the Cr(CO)3 and benzene fragments. The highest occupied molecular orbitals are mainly metal based. The nature of the lowest energy excited states were determined by time-dependent density functional theory, and the lowest energy excited state was found to have significant metal to carbonyl charge transfer character. The photochemistry of (η6-benzene)Cr(CO)3 was investigated by time-resolved infrared spectroscopy with picosecond time resolution. The low energy excited state was detected following irradiation at 400 nm, and this exhibited CO bands at lower energy than the equivalent CO bands of (η6-benzene)Cr(CO)3, consistent with metal to carbonyl charge transfer character, and is formed with excess vibrational energy, relaxing to the v = 0 vibrational state within 3 ps. The resulting {"}cold{"} excited state decays to form the CO-loss species (η6-benzene)Cr(CO)2 in approximately 70% yield and to reform (η6-benzene)Cr(CO)3 within 150 ps. The rates of relaxation from the vibrationally hot state to the cold excited state and its subsequent reaction to yield (η6-benzene)Cr(CO)2 were measured over a range of temperatures from 274 to 320 K, and the activation parameters for both processes were obtained from Eyring plots. The vibrational relaxation exhibits a negative activation enthalpy ΔH‡ (-10 (±4) kJ mol-1) and a negative activation entropy ΔS‡ (-50 (±16) J mol-1 K -1). A significant barrier (ΔH‡ = +12 (±4) kJ mol-1) was obtained for the formation of (η6-benzene)Cr(CO)2 with a ΔS‡ value close to zero. These data are used to propose a model for the CO-loss process to yield (η6-benzene)Cr(CO)2 and to explain why low temperature irradiation of (η6-benzene)Cr(CO)3 with light of wavelengths greater than 400 nm produced relatively minor amounts of (η6-benzene)Cr(CO)2.",

author = "Clark, {Ian P.} and George, {Michael W.} and Greetham, {Gregory M.} and Harvey, {Emma C.} and Conor Long and Manton, {Jennifer C.} and Pryce, {Mary T.}",

year = "2010",

month = nov,

day = "4",

doi = "10.1021/jp106290j",

language = "English",

volume = "114",

pages = "11425--11431",

journal = "Journal of Physical Chemistry A",

issn = "1089-5639",

publisher = "American Chemical Society",

number = "43",

}

Clark, IP, George, MW, Greetham, GM, Harvey, EC, Long, C, Manton, JC & Pryce, MT 2010, 'Excited state dynamics and activation parameters of remarkably slow photoinduced CO loss from (η⁶-Benzene)Cr(CO)₃ in n-heptane solution: A DFT and picosecond-time-resolved infrared study', Journal of Physical Chemistry A, vol. 114, no. 43, pp. 11425-11431. https://doi.org/10.1021/jp106290j

Excited state dynamics and activation parameters of remarkably slow photoinduced CO loss from (η⁶-Benzene)Cr(CO)₃ in n-heptane solution: A DFT and picosecond-time-resolved infrared study. / Clark, Ian P.; George, Michael W.; Greetham, Gregory M. et al.
In: Journal of Physical Chemistry A, Vol. 114, No. 43, 04.11.2010, p. 11425-11431.

Research output: Journal Publication › Article › peer-review

TY - JOUR

T1 - Excited state dynamics and activation parameters of remarkably slow photoinduced CO loss from (η6-Benzene)Cr(CO)3 in n-heptane solution

T2 - A DFT and picosecond-time-resolved infrared study

AU - Clark, Ian P.

AU - George, Michael W.

AU - Greetham, Gregory M.

AU - Harvey, Emma C.

AU - Long, Conor

AU - Manton, Jennifer C.

AU - Pryce, Mary T.

PY - 2010/11/4

Y1 - 2010/11/4

N2 - The electronic structure of (η6-benzene)Cr(CO)3 has been calculated using density functional theory and a molecular orbital interaction diagram constructed based on the Cr(CO)3 and benzene fragments. The highest occupied molecular orbitals are mainly metal based. The nature of the lowest energy excited states were determined by time-dependent density functional theory, and the lowest energy excited state was found to have significant metal to carbonyl charge transfer character. The photochemistry of (η6-benzene)Cr(CO)3 was investigated by time-resolved infrared spectroscopy with picosecond time resolution. The low energy excited state was detected following irradiation at 400 nm, and this exhibited CO bands at lower energy than the equivalent CO bands of (η6-benzene)Cr(CO)3, consistent with metal to carbonyl charge transfer character, and is formed with excess vibrational energy, relaxing to the v = 0 vibrational state within 3 ps. The resulting "cold" excited state decays to form the CO-loss species (η6-benzene)Cr(CO)2 in approximately 70% yield and to reform (η6-benzene)Cr(CO)3 within 150 ps. The rates of relaxation from the vibrationally hot state to the cold excited state and its subsequent reaction to yield (η6-benzene)Cr(CO)2 were measured over a range of temperatures from 274 to 320 K, and the activation parameters for both processes were obtained from Eyring plots. The vibrational relaxation exhibits a negative activation enthalpy ΔH‡ (-10 (±4) kJ mol-1) and a negative activation entropy ΔS‡ (-50 (±16) J mol-1 K -1). A significant barrier (ΔH‡ = +12 (±4) kJ mol-1) was obtained for the formation of (η6-benzene)Cr(CO)2 with a ΔS‡ value close to zero. These data are used to propose a model for the CO-loss process to yield (η6-benzene)Cr(CO)2 and to explain why low temperature irradiation of (η6-benzene)Cr(CO)3 with light of wavelengths greater than 400 nm produced relatively minor amounts of (η6-benzene)Cr(CO)2.

AB - The electronic structure of (η6-benzene)Cr(CO)3 has been calculated using density functional theory and a molecular orbital interaction diagram constructed based on the Cr(CO)3 and benzene fragments. The highest occupied molecular orbitals are mainly metal based. The nature of the lowest energy excited states were determined by time-dependent density functional theory, and the lowest energy excited state was found to have significant metal to carbonyl charge transfer character. The photochemistry of (η6-benzene)Cr(CO)3 was investigated by time-resolved infrared spectroscopy with picosecond time resolution. The low energy excited state was detected following irradiation at 400 nm, and this exhibited CO bands at lower energy than the equivalent CO bands of (η6-benzene)Cr(CO)3, consistent with metal to carbonyl charge transfer character, and is formed with excess vibrational energy, relaxing to the v = 0 vibrational state within 3 ps. The resulting "cold" excited state decays to form the CO-loss species (η6-benzene)Cr(CO)2 in approximately 70% yield and to reform (η6-benzene)Cr(CO)3 within 150 ps. The rates of relaxation from the vibrationally hot state to the cold excited state and its subsequent reaction to yield (η6-benzene)Cr(CO)2 were measured over a range of temperatures from 274 to 320 K, and the activation parameters for both processes were obtained from Eyring plots. The vibrational relaxation exhibits a negative activation enthalpy ΔH‡ (-10 (±4) kJ mol-1) and a negative activation entropy ΔS‡ (-50 (±16) J mol-1 K -1). A significant barrier (ΔH‡ = +12 (±4) kJ mol-1) was obtained for the formation of (η6-benzene)Cr(CO)2 with a ΔS‡ value close to zero. These data are used to propose a model for the CO-loss process to yield (η6-benzene)Cr(CO)2 and to explain why low temperature irradiation of (η6-benzene)Cr(CO)3 with light of wavelengths greater than 400 nm produced relatively minor amounts of (η6-benzene)Cr(CO)2.

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U2 - 10.1021/jp106290j

DO - 10.1021/jp106290j

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AN - SCOPUS:78049504902

SN - 1089-5639

VL - 114

SP - 11425

EP - 11431

JO - Journal of Physical Chemistry A

JF - Journal of Physical Chemistry A

IS - 43

ER -

Excited state dynamics and activation parameters of remarkably slow photoinduced CO loss from (η⁶-Benzene)Cr(CO)₃ in n-heptane solution: A DFT and picosecond-time-resolved infrared study

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