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Photoexcitation of iodide ion-pyrimidine clusters above the electron detachment threshold: Intracluster electron transfer versus nucleobase-centred excitations.
J Chem Phys. 2018 Feb 28; 148(8):084304.JC

Abstract

Laser photodissociation spectroscopy of the I-·thymine (I-·T) and I-·cytosine (I-·C) nucleobase clusters has been conducted for the first time across the regions above the electron detachment thresholds to explore the excited states and photodissociation channels. Although photodepletion is strong, only weak ionic photofragment signals are observed, indicating that the clusters decay predominantly by electron detachment. The photodepletion spectra of the I-·T and I-·C clusters display a prominent dipole-bound excited state (I) in the vicinity of the vertical detachment energy (∼4.0 eV). Like the previously studied I-·uracil (I-·U) cluster [W. L. Li et al., J. Chem. Phys. 145, 044319 (2016)], the I-·T cluster also displays a second excited state (II) centred at 4.8 eV, which we similarly assign to a π-π* nucleobase-localized transition. However, no distinct higher-energy absorption bands are evident in the spectra of the I-·C. Time-dependent density functional theory (TDDFT) calculations are presented, showing that while each of the I-·T and I-·U clusters displays a single dominant π-π* nucleobase-localized transition, the corresponding π-π* nucleobase transitions for I-·C are split across three separate weaker electronic excitations. I- and deprotonated nucleobase anion photofragments are observed upon photoexcitation of both I-·U and I-·T, with the action spectra showing bands (at 4.0 and 4.8 eV) for both the I- and deprotonated nucleobase anion production. The photofragmentation behaviour of the I-·C cluster is distinctive as its I- photofragment displays a relatively flat profile above the expected vertical detachment energy. We discuss the observed photofragmentation profiles of the I-·pyrimidine clusters, in the context of the previous time-resolved measurements, and conclude that the observed photoexcitations are primarily consistent with intracluster electron transfer dominating in the near-threshold region, while nucleobase-centred excitations dominate close to 4.8 eV. TDDFT calculations suggest that charge-transfer transitions [Iodide n (5p6) → Uracil σ*] may contribute to the cluster absorption profile across the scanned spectral region, and the possible role of these states is also discussed.

Authors+Show Affiliations

Department of Chemistry, University of York, Heslington, York YO10 5DD, United Kingdom.Department of Chemistry, University of York, Heslington, York YO10 5DD, United Kingdom.Department of Chemistry, University of York, Heslington, York YO10 5DD, United Kingdom.Department of Chemistry, University of California, Berkeley, California 94720, USA and Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.Department of Chemistry, University of York, Heslington, York YO10 5DD, United Kingdom.

Pub Type(s)

Journal Article

Language

eng

PubMed ID

29495768

Citation

Matthews, Edward, et al. "Photoexcitation of Iodide Ion-pyrimidine Clusters Above the Electron Detachment Threshold: Intracluster Electron Transfer Versus Nucleobase-centred Excitations." The Journal of Chemical Physics, vol. 148, no. 8, 2018, p. 084304.
Matthews E, Cercola R, Mensa-Bonsu G, et al. Photoexcitation of iodide ion-pyrimidine clusters above the electron detachment threshold: Intracluster electron transfer versus nucleobase-centred excitations. J Chem Phys. 2018;148(8):084304.
Matthews, E., Cercola, R., Mensa-Bonsu, G., Neumark, D. M., & Dessent, C. E. H. (2018). Photoexcitation of iodide ion-pyrimidine clusters above the electron detachment threshold: Intracluster electron transfer versus nucleobase-centred excitations. The Journal of Chemical Physics, 148(8), 084304. https://doi.org/10.1063/1.5018168
Matthews E, et al. Photoexcitation of Iodide Ion-pyrimidine Clusters Above the Electron Detachment Threshold: Intracluster Electron Transfer Versus Nucleobase-centred Excitations. J Chem Phys. 2018 Feb 28;148(8):084304. PubMed PMID: 29495768.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Photoexcitation of iodide ion-pyrimidine clusters above the electron detachment threshold: Intracluster electron transfer versus nucleobase-centred excitations. AU - Matthews,Edward, AU - Cercola,Rosaria, AU - Mensa-Bonsu,Golda, AU - Neumark,Daniel M, AU - Dessent,Caroline E H, PY - 2018/3/3/entrez PY - 2018/3/3/pubmed PY - 2018/6/27/medline SP - 084304 EP - 084304 JF - The Journal of chemical physics JO - J Chem Phys VL - 148 IS - 8 N2 - Laser photodissociation spectroscopy of the I-·thymine (I-·T) and I-·cytosine (I-·C) nucleobase clusters has been conducted for the first time across the regions above the electron detachment thresholds to explore the excited states and photodissociation channels. Although photodepletion is strong, only weak ionic photofragment signals are observed, indicating that the clusters decay predominantly by electron detachment. The photodepletion spectra of the I-·T and I-·C clusters display a prominent dipole-bound excited state (I) in the vicinity of the vertical detachment energy (∼4.0 eV). Like the previously studied I-·uracil (I-·U) cluster [W. L. Li et al., J. Chem. Phys. 145, 044319 (2016)], the I-·T cluster also displays a second excited state (II) centred at 4.8 eV, which we similarly assign to a π-π* nucleobase-localized transition. However, no distinct higher-energy absorption bands are evident in the spectra of the I-·C. Time-dependent density functional theory (TDDFT) calculations are presented, showing that while each of the I-·T and I-·U clusters displays a single dominant π-π* nucleobase-localized transition, the corresponding π-π* nucleobase transitions for I-·C are split across three separate weaker electronic excitations. I- and deprotonated nucleobase anion photofragments are observed upon photoexcitation of both I-·U and I-·T, with the action spectra showing bands (at 4.0 and 4.8 eV) for both the I- and deprotonated nucleobase anion production. The photofragmentation behaviour of the I-·C cluster is distinctive as its I- photofragment displays a relatively flat profile above the expected vertical detachment energy. We discuss the observed photofragmentation profiles of the I-·pyrimidine clusters, in the context of the previous time-resolved measurements, and conclude that the observed photoexcitations are primarily consistent with intracluster electron transfer dominating in the near-threshold region, while nucleobase-centred excitations dominate close to 4.8 eV. TDDFT calculations suggest that charge-transfer transitions [Iodide n (5p6) → Uracil σ*] may contribute to the cluster absorption profile across the scanned spectral region, and the possible role of these states is also discussed. SN - 1089-7690 UR - https://www.unboundmedicine.com/medline/citation/29495768/Photoexcitation_of_iodide_ion_pyrimidine_clusters_above_the_electron_detachment_threshold:_Intracluster_electron_transfer_versus_nucleobase_centred_excitations_ L2 - https://doi.org/10.1063/1.5018168 DB - PRIME DP - Unbound Medicine ER -