scholarly journals Probing deactivation pathways of DNA nucleobases by two-dimensional electronic spectroscopy: first principles simulations

2015 ◽  
Vol 177 ◽  
pp. 345-362 ◽  
Author(s):  
Artur Nenov ◽  
Javier Segarra-Martí ◽  
Angelo Giussani ◽  
Irene Conti ◽  
Ivan Rivalta ◽  
...  
Keyword(s):  
Excited State ◽  
Electronic Spectroscopy ◽  
Linear Response Theory ◽  
Relaxation Dynamics ◽  
Time Resolved ◽  
Complete Active Space ◽  
Near Ultraviolet ◽  
Quantum Mechanical Description ◽  
Self Consistent Field ◽  
High Level

The SOS//QM/MM [Rivalta et al., Int. J. Quant. Chem., 2014, 114, 85] method consists of an arsenal of computational tools allowing accurate simulation of one-dimensional (1D) and bi-dimensional (2D) electronic spectra of monomeric and dimeric systems with unprecedented details and accuracy. Prominent features like doubly excited local and excimer states, accessible in multi-photon processes, as well as charge-transfer states arise naturally through the fully quantum-mechanical description of the aggregates. In this contribution the SOS//QM/MM approach is extended to simulate time-resolved 2D spectra that can be used to characterize ultrafast excited state relaxation dynamics with atomistic details. We demonstrate how critical structures on the excited state potential energy surface, obtained through state-of-the-art quantum chemical computations, can be used as snapshots of the excited state relaxation dynamics to generate spectral fingerprints for different de-excitation channels. The approach is based on high-level multi-configurational wavefunction methods combined with non-linear response theory and incorporates the effects of the solvent/environment through hybrid quantum mechanics/molecular mechanics (QM/MM) techniques. Specifically, the protocol makes use of the second-order Perturbation Theory (CASPT2) on top of Complete Active Space Self Consistent Field (CASSCF) strategy to compute the high-lying excited states that can be accessed in different 2D experimental setups. As an example, the photophysics of the stacked adenine–adenine dimer in a double-stranded DNA is modeled through 2D near-ultraviolet (NUV) spectroscopy.

Excited-state dynamics of guanosine in aqueous solution revealed by time-resolved photoelectron spectroscopy: experiment and theory

2015 ◽  
Vol 17 (47) ◽  
pp. 31978-31987 ◽  
Author(s):  
Franziska Buchner ◽  
Berit Heggen ◽  
Hans-Hermann Ritze ◽  
Walter Thiel ◽  
Andrea Lübcke
Keyword(s):  
Aqueous Solution ◽  
Excited State ◽  
Photoelectron Spectroscopy ◽  
Relaxation Dynamics ◽  
Time Resolved ◽  
Excited State Dynamics ◽  
Spectroscopy Experiment

Time-resolved photoelectron spectroscopy is performed on aqueous guanosine solution to study its excited-state relaxation dynamics.

Excited-state relaxation dynamics of Re(I) tricarbonyl complexes with macrocyclic phenanthroline ligands studied by time-resolved IR spectroscopy

2009 ◽  
pp. 3941 ◽  
Author(s):  
Ana María Blanco-Rodríguez ◽  
Michael Towrie ◽  
Jean-Paul Collin ◽  
Stanislav Záliš ◽  
Antonín Vlček Jr.
Keyword(s):  
Excited State ◽  
Ir Spectroscopy ◽  
Relaxation Dynamics ◽  
Time Resolved ◽  
Phenanthroline Ligands

Observation of multi-channel non-adiabatic dynamics in aniline derivatives using time-resolved photoelectron imaging

2016 ◽  
Vol 194 ◽  
pp. 185-208 ◽  
Author(s):  
Magdalena M. Zawadzki ◽  
Marco Candelaresi ◽  
Lisa Saalbach ◽  
Stuart W. Crane ◽  
Martin J. Paterson ◽  
...  
Keyword(s):  
Excited State ◽  
Angular Distributions ◽  
Relaxation Dynamics ◽  
Photoelectron Imaging ◽  
Time Resolved ◽  
Valence States ◽  
Ultimate Fate ◽  
Site Selective ◽  
Photoelectron Angular Distributions ◽  
Electronic Character

We present results from a recent time-resolved photoelectron imaging (TRPEI) study investigating the non-adiabatic relaxation dynamics of N,N-dimethylaniline (N,N-DMA) and 3,5-dimethylaniline (3,5-DMA) following excitation at 240 nm. Analysis of the experimental data is supported by ab initio coupled-cluster calculations evaluating excited state energies and the evolution of several excited state physical properties as a function of N–H/N–CH3 bond extension – a critical reaction coordinate. The use of site-selective methylation brings considerable new insight to the existing body of literature concerning photochemical dynamics in the related system aniline at similar excitation wavelengths. The present work also builds on our own previous investigations in the same species at 250 nm. The TRPEI method provides highly differential energy- and angle-resolved data and, in particular, the temporal evolution of the photoelectron angular distributions afforded by the imaging approach offers much of the new dynamical information. In particular, we see no clear evidence of the second excited 2ππ* state non-adiabatically coupling to the lower-lying S1(ππ*) state or the mixed Rydberg/valence S2(3s/πσ*) state. This, in turn, potentially raises some unresolved questions about the overall nature of the dynamics operating in these systems, especially in regard to the 2ππ* state's ultimate fate. More generally, the findings for the aromatic systems N,N-DMA and 3,5-DMA, taken along with our recent TRPEI results for several aliphatic amine species, highlight interesting questions about the nature of electronic character evolution in mixed Rydberg-valence states as a function of certain key bond extensions and the extent of system conjugation. We begin exploring these ideas computationally for a systematically varied series of tertiary amines.

Photodynamic behavior of electronic coupling in a N-methylformamide dimer

2015 ◽  
Vol 17 (18) ◽  
pp. 12356-12364
Author(s):  
Martina Zámečníková ◽  
Dana Nachtigallová
Keyword(s):  
Perturbation Theory ◽  
Excited State ◽  
Electronic Coupling ◽  
Water Molecules ◽  
Complete Active Space ◽  
Active Space ◽  
Consistent Field ◽  
Self Consistent ◽  
Self Consistent Field

The role of the bridging water molecules has been studied during the excited state photodynamics of a N-methylformamide dimer in complex with water molecules employing the complete active space self-consistent field (CASSCF) and CAS perturbation theory (CASPT2) methods.

Femtosecond photodissociation dynamics of 1,4-diiodobenzene by gas-phase X-ray scattering and photoelectron spectroscopy

2016 ◽  
Vol 194 ◽  
pp. 525-536 ◽  
Author(s):  
Brian Stankus ◽  
James M. Budarz ◽  
Adam Kirrander ◽  
David Rogers ◽  
Joseph Robinson ◽  
...  
Keyword(s):  
Photoelectron Spectroscopy ◽  
Excited Electronic State ◽  
Bound State ◽  
Initial Study ◽  
Time Resolved ◽  
X Ray ◽  
Complete Active Space ◽  
X Ray Scattering ◽  
Self Consistent Field ◽  
Ray Scattering

We present a multifaceted investigation into the initial photodissociation dynamics of 1,4-diiodobenzene (DIB) following absorption of 267 nm radiation. We combine ultrafast time-resolved photoelectron spectroscopy and X-ray scattering experiments performed at the Linac Coherent Light Source (LCLS) to study the initial electronic excitation and subsequent rotational alignment, and interpret the experiments in light of Complete Active Space Self-Consistent Field (CASSCF) calculations of the excited electronic landscape. The initially excited state is found to be a bound 1B1 surface, which undergoes ultrafast population transfer to a nearby state in 35 ± 10 fs. The internal conversion most likely leads to one or more singlet repulsive surfaces that initiate the dissociation. This initial study is an essential and prerequisite component of a comprehensive study of the complete photodissociation pathway(s) of DIB at 267 nm. Assignment of the initially excited electronic state as a bound state identifies the mechanism as predissociative, and measurement of its lifetime establishes the time between excitation and initiation of dissociation, which is crucial for direct comparison of photoelectron and scattering experiments.

scholarly journals Ab initio studies of two pyrimidine derivatives as possible photo-switch systems

Open Physics ◽  
2013 ◽  
Vol 11 (9) ◽  
Author(s):  
András Csehi ◽  
Clemens Woywod ◽  
Gábor Halász ◽  
Ágnes Vibók
Keyword(s):  
Excited State ◽  
Hydrogen Transfer ◽  
Covalent Bond ◽  
Excitation Energies ◽  
Complete Active Space ◽  
Vertical Excitation ◽  
Singlet States ◽  
Self Consistent Field ◽  
Intramolecular Hydrogen ◽  
Vertical Excitation Energies

AbstractThe six lowest lying electronic singlet states of 8-(pyrimidine-2-yl)quinolin-ol and 2-(4-nitropyrimidine-2-yl)ethenol have been studied theoretically using the complete active space self-consistent-field (CASSCF) and M’ller-Plesset second-order perturbation theory (MP2) methods. Both molecules can be viewed as consisting of a frame and a crane component. As a possible mechanism for the excited-state relaxation process an intramolecular hydrogen transfer promoted by twisting around the covalent bond connecting the molecular frame and crane moieties has been considered. Based on this idea we have attempted to derive abstracted photochemical pathways for both systems. Geometry optimizations for the construction of hypothetical reaction coordinates have been performed at the MP2 level of theory while the CASSCF approach has been employed for the calculation of vertical excitation energies along the pathways. The results of the calculations along the specific twisting displacements investigated in this study do not support the notion of substantial twisting activity upon excitation of any of the five excited states at the planar terminal structures of the torsion coordinates of both molecules. However, the present analysis should be considered only as a first, preliminary step towards an understanding of the photochemistry of the two candidate compounds. For example, we have not performed any excited state geometry optimizations so far and the estimates of vertical excitation energies do not take dynamical electron correlation into account. Further work on this subject is in progress.

scholarly journals Altered relaxation dynamics of excited state reactions by confinement in reverse micelles probed by ultrafast fluorescence up-conversion

2021 ◽  
Author(s):  
Ismael A. Heisler ◽  
Stephen R. Meech
Keyword(s):  
Excited State ◽  
Real Time ◽  
Reverse Micelles ◽  
Reaction Dynamics ◽  
Time Study ◽  
Relaxation Dynamics ◽  
Time Resolved Fluorescence ◽  
Time Resolved

Time resolved fluorescence follows reaction dynamics in real-time. Study of reaction which are sensitive to their environment allowed the effect of confinement to be observed and studied.

scholarly journals Are Multicentre Bond Indices and Related Quantities Reliable Predictors of Excited-State Aromaticity?

Molecules ◽  
2020 ◽  
Vol 25 (20) ◽  
pp. 4791
Author(s):  
Robert Ponec ◽  
David L. Cooper ◽  
Peter B. Karadakov
Keyword(s):  
Excited State ◽  
Excited States ◽  
Similarity Index ◽  
Triplet States ◽  
Complete Active Space ◽  
First Order ◽  
Consistent Field ◽  
Self Consistent Field ◽  
Singlet And Triplet States ◽  
Bond Indices

Systematic scrutiny is carried out of the ability of multicentre bond indices and the NOEL-based similarity index dAB to serve as excited-state aromaticity criteria. These indices were calculated using state-optimized complete active-space self-consistent field wavefunctions for several low-lying singlet and triplet states of the paradigmatic molecules of benzene and square cyclobutadiene and the inorganic ring S2N2. The comparison of the excited-state indices with aromaticity trends for individual excited states suggested by the values of magnetic aromaticity criteria show that whereas the indices work well for aromaticity reversals between the ground singlet and first triplet electronic states, addressed by Baird’s rule, there are no straightforward parallels between the two sets of data for singlet excited states. The problems experienced while applying multicentre bond indices and dAB to singlet excited states are explained by the loss of the information inherently present in wavefunctions and/or pair densities when calculating the first-order density matrix.

Ligand mediated excited state carrier relaxation dynamics of Cd1−xZnxSe1−ySy NCs derived from bile salts

2017 ◽  
Vol 5 (20) ◽  
pp. 4977-4984 ◽  
Author(s):  
Sayantan Chatterjee ◽  
Uday Maitra
Keyword(s):  
Excited State ◽  
Bile Acid ◽  
Bile Salts ◽  
Single Step ◽  
Relaxation Dynamics ◽  
Time Resolved ◽  
Carrier Relaxation ◽  
Time Resolved Spectroscopy ◽  
Carrier Relaxation Dynamics

Bile acid derived cadmium and zinc precursors were utilized for an efficient and single step synthesis of Cd1−xZnxSe1−ySy NCs. Different capping ligand induced carrier relaxation dynamics of the NCs using time resolved spectroscopy was also studied.

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