The Effect of Methylation on the Triplet-State Dynamics of 2-Thiouracil: Time-Resolved Photoelectron Spectroscopy of 2-Thiothymine

Ullrich, Susanne; Qu, Yingqi; Mohamadzade, Abed; Shrestha, Sarita

doi:10.1021/acs.jpca.2c06051

Cited by 3 publications

(3 citation statements)

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“…Although this pathway leads to a thermodynamically more stable species by overcoming a small potential barrier (0.21 eV), it requires redistribution of vibrational energy from the hot sulfur 2 bending modes into initially cold sulfur 4 in-plane modes. A similar process has been reported to occur in 2-TU, but for a distinctly different triplet topography with two isoenergetic minima . The initially populated sulfur 2 out-of-plane minimum resembles Min- 3 π S2 π S2 * and barrier crossing to the ring-distorted minimum, comparable to Min- 3 π S4 π S4 * , which requires a similar vibrational mode change.…”

Section: Resultsmentioning

confidence: 99%

“…A similar process has been reported to occur in 2-TU, but for a distinctly different triplet topography with two isoenergetic minima. 57 The initially populated sulfur 2 out-of-plane minimum resembles Min-3 π S2 π S2 * and barrier crossing to the ring-distorted minimum, comparable to Min-3 π S4 π S4 * , which requires a similar vibrational mode change. This process was found to occur on ps to ns timescales.…”

Section: Journal Of the American Chemical Societymentioning

confidence: 97%

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Double Thionated Pyrimidine Nucleobases: Molecular Tools with Tunable Photoproperties

et al. 2023

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Sulfur-substituted nucleobases are DNA and RNA base derivatives that exhibit extremely efficient photoinduced intersystem crossing (ISC) dynamics into the lowest-energy triplet state. The long-lived and reactive triplet states of sulfur-substituted nucleobases are crucial due to their wide range of potential applications in medicine, structural biology, and the development of organic light-emitting diodes (OLEDs) and other emerging technologies. However, a comprehensive understanding of nonnegligible wavelength-dependent changes in the internal conversion (IC) and ISC events is still lacking. Here, we study the underlying mechanism using joint experimental gas-phase time-resolved photoelectron spectroscopy (TRPES) and theoretical quantum chemistry methods. We combine 2,4-dithiouracil (2,4-DTU) TRPES experimental data with computational analysis of the different photodecay processes, which are induced by increasing excitation energies along the entire linear absorption (LA) ultraviolet (UV) spectrum. Our results show how the double-thionated uracil (U), i.e., 2,4-DTU, appears as a versatile photoactivatable instrument. Multiple decay processes can be initiated with different ISC rates or triplet-state lifetimes that resemble the distinctive behavior of the singly substituted 2-or 4-thiouracil (2-TU or 4-TU). We obtained a clear partition of the LA spectrum based on the dominant photoinduced process. Our work clarifies the reasons behind the wavelength-dependent changes in the IC, ISC, and triplet-state lifetimes in doubly thionated U, becoming a biological system of utmost importance for wavelength-controlled applications. These mechanistic details and photoproperties are transferable to closely related molecular systems such as thionated thymines.

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Section: Resultsmentioning

confidence: 99%

Section: Journal Of the American Chemical Societymentioning

confidence: 97%

Double Thionated Pyrimidine Nucleobases: Molecular Tools with Tunable Photoproperties

et al. 2023

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“…[1][2][3][4][5][6][7][8] In contrast, single atom substitutions, such as the replacement of one or both nucleobase oxygens with sulfur atoms, have been shown to have profound impacts on relaxation pathways following photoexcitation. [9][10][11][12][13][14][15][16][17] These nucleobase derivatives are of interest owing to their potential for pharmacological applications such as phototherapy where they can act as photosensitizers. 9-11, 18, 19 For example, upon photoexcitation of sulfur substituted nucleobases, the quantum yield for relaxation to the triplet manifold nears unity, resulting in increased reactivity compared to canonical nucleobases that undergo rapid relaxation to their ground electronic states.…”

Section: Introductionmentioning

confidence: 99%

Time resolved photoelectron spectroscopy of iodide-4-thiouracil cluster: the pi/pi star state as a doorway for electron attachment

Asplund,

Koga,

et al. 2023

Preprint

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The photophysics of thiobases — nucleobases in which one or more oxygen atoms are replaced with sulfur atoms — have been shown to vary greatly depending on the location of sulfonation. Not only are direct dynamics of the neutral thiobase impacted, but also the dynamics of excess electron accommodation. In this work, time resolved photoelectron spectroscopy (TRPES) is used to measure binary anionic clusters of iodide and 4-thiouracil, Iˉ4TU. We investigate charge transfer dynamics driven by excitation at 3.88 eV, corresponding to the lowest ππ* transition of the thiouracil, and 4.16 eV, near the cluster vertical detachment energy. The photoexcited state dynamics are probed by photodetachment with 1.55 eV and 3.146 eV pulses. Excitation at 3.88 eV leads to signal from the valence-bound ion only, indicating a charge accommodation mechanism that does not utilize the dipole-bound anion as an intermediate. Excitation at 4.16 eV rapidly gives rise to dipole-bound and valence-bound ion signals, with a second rise in valence-bound signal corresponding to the decay of the dipole-bound signal. The dynamics associated with the low energy ππ* excitation of 4-thiouracil provide clear experimental proof for the importance of localized excitation and electron backfilling in halide-nucleobase clusters.

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Time-resolved photoelectron spectroscopy of iodide–4-thiouracil cluster: The ππ* state as a doorway for electron attachment

Asplund,

Koga,

et al. 2024

The Journal of Chemical Physics

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The photophysics of thiobases—nucleobases in which one or more oxygen atoms are replaced with sulfur atoms— vary greatly depending on the location of sulfonation. Not only are direct dynamics of a neutral thiobase impacted, but also the dynamics of excess electron accommodation. In this work, time-resolved photoelectron spectroscopy is used to measure binary anionic clusters of iodide and 4-thiouracil, I− · 4TU. We investigate charge transfer dynamics driven by excitation at 3.88 eV, corresponding to the lowest ππ* transition of the thiouracil, and at 4.16 eV, near the cluster vertical detachment energy. The photoexcited state dynamics are probed by photodetachment with 1.55 and 3.14 eV pulses. Excitation at 3.88 eV leads to a signal from a valence-bound ion only, indicating a charge accommodation mechanism that does not involve a dipole-bound anion as an intermediate. Excitation at 4.16 eV rapidly gives rise to dipole-bound and valence-bound ion signals, with a second rise in the valence-bound signal corresponding to the decay of the dipole-bound signal. The dynamics associated with the low energy ππ* excitation of 4-thiouracil provide a clear experimental proof for the importance of localized excitation and electron backfilling in halide–nucleobase clusters.

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The Effect of Methylation on the Triplet-State Dynamics of 2-Thiouracil: Time-Resolved Photoelectron Spectroscopy of 2-Thiothymine

Cited by 3 publications

References 25 publications

Double Thionated Pyrimidine Nucleobases: Molecular Tools with Tunable Photoproperties

Double Thionated Pyrimidine Nucleobases: Molecular Tools with Tunable Photoproperties

Time resolved photoelectron spectroscopy of iodide-4-thiouracil cluster: the pi/pi star state as a doorway for electron attachment

Time-resolved photoelectron spectroscopy of iodide–4-thiouracil cluster: The ππ* state as a doorway for electron attachment

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