scholarly journals Tracking excited state decay mechanisms of pyrimidine nucleosides in real time

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Rocío Borrego-Varillas ◽  
Artur Nenov ◽  
Piotr Kabaciński ◽  
Irene Conti ◽  
Lucia Ganzer ◽  
...  
Keyword(s):  
Excited State ◽  
Transient Absorption ◽  
Building Blocks ◽  
Transient Absorption Spectroscopy ◽  
Classical Dynamics ◽  
Spectral Signatures ◽  
Spectral Signal ◽  
Order Of Magnitude ◽  
Franck Condon ◽  
Intense Debate

AbstractDNA owes its remarkable photostability to its building blocks—the nucleosides—that efficiently dissipate the energy acquired upon ultraviolet light absorption. The mechanism occurring on a sub-picosecond time scale has been a matter of intense debate. Here we combine sub-30-fs transient absorption spectroscopy experiments with broad spectral coverage and state-of-the-art mixed quantum-classical dynamics with spectral signal simulations to resolve the early steps of the deactivation mechanisms of uridine (Urd) and 5-methyluridine (5mUrd) in aqueous solution. We track the wave packet motion from the Franck-Condon region to the conical intersections (CIs) with the ground state and observe spectral signatures of excited-state vibrational modes. 5mUrd exhibits an order of magnitude longer lifetime with respect to Urd due to the solvent reorganization needed to facilitate bulky methyl group motions leading to the CI. This activates potentially lesion-inducing dynamics such as ring opening. Involvement of the 1nπ* state is found to be negligible.

Tracking excited state decay mechanisms of pyrimidine nucleosides in real time

2020 ◽  
Author(s):  
Giulio Cerullo ◽  
Rocio Borrego-Varillas ◽  
Artur Nenov ◽  
Piotr Kabacinski ◽  
Irene Conti ◽  
...  
Keyword(s):  
Excited State ◽  
Quantum Dynamics ◽  
Transient Absorption ◽  
Building Blocks ◽  
Electronic Energy ◽  
Transient Absorption Spectroscopy ◽  
Spectral Signature ◽  
Dna Strands ◽  
Order Of Magnitude ◽  
Dynamics Simulations

Abstract DNA owes its remarkable photostability to the ability of its building blocks – the nucleosides – to efficiently dissipate the excess electronic energy acquired upon photoexcitation with ultraviolet light. The exact mechanism occurring on a sub-picosecond time scale has been a matter of intense debate. Here we combine sub-30-fs transient absorption spectroscopy with broad spectral coverage and state-of-the-art quantum dynamics simulations to resolve the early steps of the deactivation mechanisms of uridine (Urd) and 5-methyluridine (5mUrd) in aqueous solution. For both nucleosides we track the wave packet motion from the Franck-Condon region to the conical intersection (CI) with to the ground state and observe a direct spectral signature of an excited-state vibrational mode leading to the CI. We find that 5mUrd exhibits an order of magnitude longer excited state lifetime with respect to Urd and assign it to the larger inertia of the methyl group involved in the ring puckering mode leading to the CI. We argue that this longer lifetime enables the activation of potentially lesion-inducing coordinates such as ring opening, elucidating the origin of the susceptibility of thymine-containing DNA strands to photodamage.

The geometry relaxation and photodeactivation from the S2 state of dibenzofuran studied by ultrafast spectroscopy

2020 ◽  
Vol 234 (7-9) ◽  
pp. 1495-1506 ◽  
Author(s):  
Lian Wang ◽  
Song Zhang ◽  
Ye Wang ◽  
Bing Zhang
Keyword(s):  
Excited State ◽  
Internal Conversion ◽  
Transient Absorption ◽  
Excited State Absorption ◽  
Transient Absorption Spectroscopy ◽  
Femtosecond Transient Absorption ◽  
Pharmaceutically Active Compound ◽  
S2 State ◽  
Franck Condon ◽  
T State

AbstractDibenzofuran (DBF) has attracted much attention from scientists recently since it is applied as a photoluminescence material and pharmaceutically active compound. Since the polychlorinated derivatives are highly toxic and manifest photostability in the environment. Femtosecond transient absorption spectroscopy associated with quantum chemical calculations are employed to investigate the ultrafast excited state dynamics of dibenzofuran from the S2 state in 1,4-dioxane and ethanol, respectively. Following excitation at a wavelength of 266 nm, the S2 state is firstly populated in the Franck–Condon region and preserves the planar molecular structure of the ground state. The observed increase of the transient absorption spectra of the excited state within the first several picoseconds indicates a geometry relaxation occurring on the S2 potential energy surface. The subsequent kinetic traces of excited state absorption show that the S2 state in the adiabatic region decays to the S1 state through a fast internal conversion, followed by intersystem crossing to the T1 state with a decay time of tens and hundreds of picoseconds in ethanol and 1,4-dioxane, respectively. Finally, the deactivation processes from the S1 or T state are slow and take place on a time scale of about 20 ns.

Excited-State Dynamics in the RNA Nucleotide Uridine 5’-Monophosphate Investigated by Femtosecond Broadband Transient Absorption Spectroscopy

2019 ◽  
Author(s):  
Matthew M. Brister ◽  
Carlos Crespo-Hernández
Keyword(s):  
Excited State ◽  
Excited States ◽  
Ground State ◽  
Transient Absorption ◽  
Electronic Energy ◽  
Transient Absorption Spectroscopy ◽  
Electronic Relaxation ◽  
Vibrationally Excited ◽  
Excited State Dynamics ◽  
Π State

<p></p><p> Damage to RNA from ultraviolet radiation induce chemical modifications to the nucleobases. Unraveling the excited states involved in these reactions is essential, but investigations aimed at understanding the electronic-energy relaxation pathways of the RNA nucleotide uridine 5’-monophosphate (UMP) have not received enough attention. In this Letter, the excited-state dynamics of UMP is investigated in aqueous solution. Excitation at 267 nm results in a trifurcation event that leads to the simultaneous population of the vibrationally-excited ground state, a longlived <sup>1</sup>n<sub>O</sub>π* state, and a receiver triplet state within 200 fs. The receiver state internally convert to the long-lived <sup>3</sup>ππ* state in an ultrafast time scale. The results elucidate the electronic relaxation pathways and clarify earlier transient absorption experiments performed for uracil derivatives in solution. This mechanistic information is important because long-lived nπ* and ππ* excited states of both singlet and triplet multiplicities are thought to lead to the formation of harmful photoproducts.</p><p></p>

Photoinduced electron transfer dynamics in dye-sensitized ZnO nanowire photoanodes

2018 ◽  
Vol 32 (19) ◽  
pp. 1840049
Author(s):  
Akihiro Furube ◽  
Takahiro Arai ◽  
Masahiro Okazaki ◽  
Shinichiro Yanagiya ◽  
Liang-Yih Chen ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Excited State ◽  
Transient Absorption ◽  
Low Cost ◽  
Transient Absorption Spectroscopy ◽  
Zno Nanowire ◽  
Dye Sensitized ◽  
Femtosecond Transient Absorption ◽  
State Formula ◽  
Flexible Solar Cell

A photoanode using dye-sensitized ZnO nanowire (NW) is a good candidate for low-cost, colorful, light-weight and flexible solar cell material. We have synthesized a ZnO NW anode and a ZnO nanowire–nanoparticle (NWNP) anode, in which ZnO nanoparticles (NPs) are decollated on the surface of NWs. Photo-induced electron transfer dynamics from the excited state of sensitizer dye (D149) to the conduction band of ZnO NW and ZnO NWNP was clarified using femtosecond transient absorption spectroscopy. The decay of the single excited state ([Formula: see text]) of D149 was faster in ZnO NW than that of ZnO NWNP, indicating that NW is more suitable as an efficient electron acceptor.

Photoinduced ligand dissociation follows reverse energy gap law: nitrile photodissociation from low energy 3MLCT excited states

2020 ◽  
Vol 56 (29) ◽  
pp. 4070-4073
Author(s):  
Lauren M. Loftus ◽  
Jeffrey J. Rack ◽  
Claudia Turro
Keyword(s):  
Excited State ◽  
Excited States ◽  
Absorption Spectroscopy ◽  
Transient Absorption ◽  
Energy Gap ◽  
Low Energy ◽  
Transient Absorption Spectroscopy ◽  
Ligand Dissociation ◽  
Energy Gap Law

Transient absorption spectroscopy is used to show that stabilization of the 3MLCT excited state in a series of Ru(ii) complexes leads to decreased population of the 3LF state, but does not reduce the efficiency of photoinduced nitrile dissociation.

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