Excited-State Intramolecular Hydrogen Transfer (ESIHT) of 1,8-Dihydroxy-9,10-anthraquinone (DHAQ) Characterized by Ultrafast Electronic and Vibrational Spectroscopy and Computational Modeling

2014 ◽  
Vol 118 (17) ◽  
pp. 3090-3099 ◽  
Author(s):  
Omar F. Mohammed ◽  
Dequan Xiao ◽  
Victor S. Batista ◽  
Erik T. J. Nibbering
Keyword(s):  
Excited State ◽  
Computational Modeling ◽  
Vibrational Spectroscopy ◽  
Hydrogen Transfer ◽  
Intramolecular Hydrogen

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 Probing Competing Relaxation Pathways in Malonaldehyde with Transient X-Ray Absorption Spectroscopy

2020 ◽  
Author(s):  
Nanna Holmgaard List ◽  
Adrian L. Dempwolff ◽  
Andreas Dreuw ◽  
Patrick Norman ◽  
Todd J. Martínez
Keyword(s):  
Excited State ◽  
Absorption Spectroscopy ◽  
Hydrogen Transfer ◽  
Intersystem Crossing ◽  
Light Sources ◽  
X Ray ◽  
Valence States ◽  
Specific Mapping ◽  
Intramolecular Hydrogen ◽  
X Ray Absorption

<p>Excited-state intramolecular hydrogen transfer (ESIHT) is a fundamental reaction relevant to chemistry and biology. Malonaldehyde is the simplest example of ESIHT, yet only little is known experimentally about its excited-state dynamics. Several competing relaxation pathways have been proposed, including internal conversion mediated by ESIHT and C=C torsional motion as well as intersystem crossing. We perform an in silico transient X-ray absorption spectroscopy (TRXAS) experiment at the oxygen K-edge to investigate its potential to monitor the proposed ultrafast decay pathways in malonaldehyde upon photoexcitation to its bright S2(pp*) state. We employ both restricted active space perturbation theory and algebraic diagrammatic construction for the polarization propagator along interpolated reaction coordinates as well as representative trajectories from ab initio multiple spawning simulations to compute the TRXAS signals from the lowest valence states. Our study suggests that oxygen K-edge TRXAS can distinctly fingerprint the passage through the H-transfer intersection and the concomitant population transfer to the S1(np*) state. Potential intersystem crossing to T1(pp*) is detectable from reappearance of the double pre-edge signature and reversed intensities. Moreover, the torsional deactivation pathway induces transient charge redistribution from the enol side towards the central C-atom and manifests itself as substantial shifts of the pre-edge features. Given the continuous advances in X-ray light sources, our study proposes an experimental route to disentangle ultrafast excited-state decay channels in this prototypical ESIHT system and provides a pathway-specific mapping of the TRXAS signal to facilitate the interpretation of future experiments.</p>

scholarly journals Excited-State Intramolecular Hydrogen Transfer of Compact Molecules Controls Amyloid Aggregation Profiles

2021 ◽  
Author(s):  
Mannkyu Hong ◽  
Mingeun Kim ◽  
Jiwon Yoon ◽  
Seung-Hee Lee ◽  
Mu-Hyun Baik ◽  
...  
Keyword(s):  
Excited State ◽  
Hydrogen Transfer ◽  
Experimental Studies ◽  
Amyloid Β ◽  
Molecular Structures ◽  
Hydroxyl Groups ◽  
Chemical Reagents ◽  
Amyloidogenic Peptides ◽  
Intramolecular Hydrogen

Designing new chromophores by tuning their molecular structures and optimizing their photophysical properties leads to suitable photochromic features. Herein, we report a series of anthraquinone (AQ)-based photosensitizers that undergoes excited-state intramolecular hydrogen transfer and effectively oxidizes amyloidogenic peptides, which significantly affects the subsequent aggregation pathways. DFT calculations showed that the appropriate position of the hydroxyl groups in the AQ backbone and the consequent intramolecular hydrogen transfer can facilitate the energy transfer to triplet oxygen. Biochemical and biophysical investigations confirmed that these photoactive chemical reagents are able to oxidatively modify both metal-free amyloid-β (Aβ) and metal-bound Aβ, thereby redirecting their on-pathway aggregation into off-pathway as well as disassembling their pre-formed aggregates. Moreover, the in vivo histochemical analysis of Aβ species produced upon photoactivation of the most promising candidate demonstrated that they do not aggregate into toxic oligomeric or fibrillar aggregates in the brain. Overall, our combined computational and experimental studies validate a light-based approach for designing small molecules as chemical reagents targeting and controlling amyloidogenic peptides associated with neurodegenerative disorders.

scholarly journals Probing Competing Relaxation Pathways in Malonaldehyde with Transient X-Ray Absorption Spectroscopy

2020 ◽  
Author(s):  
Nanna Holmgaard List ◽  
Adrian L. Dempwolff ◽  
Andreas Dreuw ◽  
Patrick Norman ◽  
Todd J. Martínez
Keyword(s):  
Excited State ◽  
Absorption Spectroscopy ◽  
Hydrogen Transfer ◽  
Intersystem Crossing ◽  
Light Sources ◽  
X Ray ◽  
Valence States ◽  
Specific Mapping ◽  
Intramolecular Hydrogen ◽  
X Ray Absorption

<p>Excited-state intramolecular hydrogen transfer (ESIHT) is a fundamental reaction relevant to chemistry and biology. Malonaldehyde is the simplest example of ESIHT, yet only little is known experimentally about its excited-state dynamics. Several competing relaxation pathways have been proposed, including internal conversion mediated by ESIHT and C=C torsional motion as well as intersystem crossing. We perform an in silico transient X-ray absorption spectroscopy (TRXAS) experiment at the oxygen K-edge to investigate its potential to monitor the proposed ultrafast decay pathways in malonaldehyde upon photoexcitation to its bright S2(pp*) state. We employ both restricted active space perturbation theory and algebraic diagrammatic construction for the polarization propagator along interpolated reaction coordinates as well as representative trajectories from ab initio multiple spawning simulations to compute the TRXAS signals from the lowest valence states. Our study suggests that oxygen K-edge TRXAS can distinctly fingerprint the passage through the H-transfer intersection and the concomitant population transfer to the S1(np*) state. Potential intersystem crossing to T1(pp*) is detectable from reappearance of the double pre-edge signature and reversed intensities. Moreover, the torsional deactivation pathway induces transient charge redistribution from the enol side towards the central C-atom and manifests itself as substantial shifts of the pre-edge features. Given the continuous advances in X-ray light sources, our study proposes an experimental route to disentangle ultrafast excited-state decay channels in this prototypical ESIHT system and provides a pathway-specific mapping of the TRXAS signal to facilitate the interpretation of future experiments.</p>

scholarly journals Revealing the role of excited state proton transfer (ESPT) in excited state hydrogen transfer (ESHT): systematic study in phenol–(NH3)n clusters

2021 ◽  
Author(s):  
Christophe Jouvet ◽  
Mitsuhiko Miyazaki ◽  
Masaaki Fujii
Keyword(s):  
Excited State ◽  
Proton Transfer ◽  
Systematic Study ◽  
General Model ◽  
Hydrogen Transfer ◽  
Excited State Proton Transfer

A general model of excited state hydrogen transfer (ESHT) which unifies ESHT and the excited state proton transfer (ESPT) is presented from experimental and theoretical works on phenol–(NH3)n. The hidden role of ESPT is revealed.

scholarly journals UV-induced hydrogen transfer in DNA base pairs promoted by dark nπ* states

2020 ◽  
Vol 56 (2) ◽  
pp. 201-204 ◽  
Author(s):  
Kinga E. Szkaradek ◽  
Petr Stadlbauer ◽  
Jiří Šponer ◽  
Robert W. Góra ◽  
Rafał Szabla
Keyword(s):  
Excited State ◽  
Hydrogen Transfer ◽  
Base Pairs ◽  
Dna Base ◽  
Dna Base Pairs

Formation of an excited-state complex enables ultrafast photorelaxation of dark nπ* states in GC and HC base pairs.

Intracluster hydrogen transfer followed by dissociation in the phenol–(NH3)3 excited state: PhOH(S1)–(NH3)3→PhO•+(NH4)(NH3)2

1999 ◽  
Vol 111 (24) ◽  
pp. 10747-10749 ◽  
Author(s):  
G. A. Pino ◽  
C. Dedonder-Lardeux ◽  
G. Grégoire ◽  
C. Jouvet ◽  
S. Martrenchard ◽  
...  
Keyword(s):  
Excited State ◽  
Hydrogen Transfer
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