Intersystem crossing dynamics in singly substituted thiouracil studied by time-resolved photoelectron spectroscopy: Micro-environmental effects due to sulfur position

Mohamadzade, Abed; Bai, Shuming; Barbatti, Mario; Ullrich, Susanne

doi:10.1016/j.chemphys.2018.08.011

Cited by 21 publications

(32 citation statements)

References 58 publications

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“…Eventually, the population is trapped in the lowest triplet state in each channel ( 3 ππ*/ 3 ππ*′). Our calculations strongly suggest the involvement of the dark nπ*/nπ*′ states in the non‐adiabatic decay, in agreement with a previous dynamical calculation and time‐resolved photoelectron spectroscopy experiments in the gas phase . Nonetheless, the fingerprint PA signals of the nπ*/nπ*′ states are either weak in intensity (e.g., 24TU; for more details see Figures S6 and S7 in the Supporting Information) or coincide with more intense PA signals coming from the ππ*/ππ*′ states and the triplet manifold (e.g., 2TU; Figure S4, Supporting Information).…”

Section: Resultsmentioning

confidence: 99%

“…[8,9,[18][19][20] To date, transienta bsorption (TA) spectroscopy experiments, with approximately 200-fs time resolution,f or 2-thiouracil (2TU), 4-thiouracil (4TU) and 2,4-dithiouracil (24TU) have shown an ultrafastI SC occurringw ithin hundreds of femtoseconds. [7,10,21] For 2TU [21][22][23][24][25][26][27] and 4TU, [28,29] high-level calculations have pointed out two possible energyr elaxation pathways from the lowestb right exciteds inglet state:d irect ISC to the triplet manifold or at wo-step process, whereby the population of the triplet state is mediated by ad ark singlet state of np*s ymmetry. [18,20,21,23,24,26,[28][29][30][31][32][33] However,c omprehensive experimental data with high enough time resolution and calculations mappinga ll the simultaneously populated decay paths are still lacking for this class of compounds,p reventing ad etailed picture of the ultrafast triplets tate formationm echanisms.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

A Unified Experimental/Theoretical Description of the Ultrafast Photophysics of Single and Double Thionated Uracils

Teles-Ferreira

Conti

Borrego-Varillas

et al. 2019

Chemistry A European J

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Photoinduced processes in thiouracil derivatives have lately attracted considerable attention due to their suitability for innovative biological and pharmacological applications. Here, sub‐20 fs broadband transient absorption spectroscopy in the near‐UV are combined with CASPT2/MM decay path calculations to unravel the excited‐state decay channels of water solvated 2‐thio and 2,4‐dithiouracil. These molecules feature linear absorption spectra with overlapping ππ* bands, leading to parallel decay routes which we systematically track for the first time. The results reveal that different processes lead to the triplet states population, both directly from the ππ* absorbing state and via the intermediate nπ* dark state. Moreover, the 2,4‐dithiouracil decay pathways is shown to be strongly correlated either to those of 2‐ or 4‐thiouracil, depending on the sulfur atom on which the electronic transition localizes.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

A Unified Experimental/Theoretical Description of the Ultrafast Photophysics of Single and Double Thionated Uracils

Teles-Ferreira

Conti

Borrego-Varillas

et al. 2019

Chemistry A European J

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“…12 Particular attention has been devoted to thiobases analogues—in which oxygen atoms are replaced by sulfur—because, unlike their canonical counterparts, intersystem crossing results in high quantum yields of triplet states. 13 − 20 For instance, 6-thioguanine (6tG) has an intersystem crossing quantum yield of ca. 60%.…”

Section: Introductionmentioning

confidence: 99%

Excited-State Properties and Relaxation Pathways of Selenium-Substituted Guanine Nucleobase in Aqueous Solution and DNA Duplex

et al. 2021

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The excited-state properties and relaxation mechanisms after light irradiation of 6-selenoguanine (6SeG) in water and in DNA have been investigated using a quantum mechanics/molecular mechanics (QM/MM) approach with the multistate complete active space second-order perturbation theory (MS-CASPT2) method. In both environments, the S 1 1 (n Se π 5 * ) and S 2 1 (π Se π 5 * ) states are predicted to be the spectroscopically dark and bright states, respectively. Two triplet states, T 1 3 (π Se π 5 * ) and T 2 3 (n Se π 5 * ), are found energetically below the S 2 state. Extending the QM region to include the 6SeG-Cyt base pair slightly stabilizes the S 2 state and destabilizes the S 1 , due to hydrogen-bonding interactions, but it does not affect the order of the states. The optimized minima, conical intersections, and singlet–triplet crossings are very similar in water and in DNA, so that the same general mechanism is found. Additionally, for each excited state geometry optimization in DNA, three kind of structures (“up”, “down”, and “central”) are optimized which differ from each other by the orientation of the C=Se group with respect to the surrounding guanine and thymine nucleobases. After irradiation to the S 2 state, 6SeG evolves to the S 2 minimum, near to a S 2 /S 1 conical intersection that allows for internal conversion to the S 1 state. Linear interpolation in internal coordinates indicate that the “central” orientation is less favorable since extra energy is needed to surmount the high barrier in order to reach the S 2 /S 1 conical intersection. From the S 1 state, 6SeG can further decay to the T 1 3 (π Se π 5 * ) state via intersystem crossing, where it will be trapped due to the existence of a sizable energy barrier between the T 1 minimum and the T 1 /S 0 crossing point. Although this general S 2 → T 1 mechanism takes place in both media, the presence of DNA induces a steeper S 2 potential energy surface, that it is expected to accelerate the S 2 → S 1 internal conversion.

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“…The CASPT2 trajectory calculations of Mai et al [23], display a S2-S1 internal conversion on the order of 60 fs (below our time-resolution), with an S1 state lifetime of 400-500 fs [23]. This interpretation is also chosen in previous experiments [18,19,40]. Afterwards, the T1 and T2 state become populated via an intersystem crossing with the S1.…”

Section: Discussionmentioning

confidence: 57%

Ultrafast dynamics of 2-thiouracil investigated by time-resolved Auger spectroscopy

Lever

Mayer

Picconi

et al. 2020

J. Phys. B: At. Mol. Opt. Phys.

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We present time-resolved ultraviolet-pump x-ray probe Auger spectra of 2-thiouracil. An ultraviolet induced shift towards higher kinetic energies is observed in the sulfur 2p Auger decay. The difference Auger spectra of pumped and unpumped molecules exhibit ultrafast dynamics in the shift amplitude, in which three phases can be recognized. In the first 100 fs, a shift towards higher kinetic energies is observed, followed by a 400 fs shift back to lower kinetic energies and a 1 ps shift again to higher kinetic energies. We use a simple Coulomb-model, aided by quantum chemical calculations of potential energy states, to deduce a C-S bond expansion within the first 100 fs. The bond elongation triggers internal conversion from the photoexcited S2 to the S1 state. Based on timescales, the subsequent dynamics can be interpreted in terms of S1 nuclear relaxation and S1-triplet internal conversion.

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Intersystem crossing dynamics in singly substituted thiouracil studied by time-resolved photoelectron spectroscopy: Micro-environmental effects due to sulfur position

Cited by 21 publications

References 58 publications

A Unified Experimental/Theoretical Description of the Ultrafast Photophysics of Single and Double Thionated Uracils

A Unified Experimental/Theoretical Description of the Ultrafast Photophysics of Single and Double Thionated Uracils

Excited-State Properties and Relaxation Pathways of Selenium-Substituted Guanine Nucleobase in Aqueous Solution and DNA Duplex

Ultrafast dynamics of 2-thiouracil investigated by time-resolved Auger spectroscopy

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