1,721,018 research outputs found
Photoprotecting uracil by coupling with lossy nanocavities
Full text linkWe analyze how the photorelaxation dynamics of a molecule can be controlled by modifying its electromagnetic environment using a nanocavity mode. In particular, we consider the photorelaxation of the RNA nucleobase uracil, which is the natural mechanism to prevent photodamage. In our theoretical work, we identify the operative conditions in which strong coupling with the cavity mode can open an efficient photoprotective channel, resulting in a relaxation dynamics twice as fast as the natural one. We rely on a state-of-the-art chemically detailed molecular model and a non-Hermitian Hamiltonian propagation approach to perform full-quantum simulations of the system dissipative dynamics. By focusing on the photon decay, our analysis unveils the active role played by cavity-induced dissipative processes in modifying chemical reaction rates, in the context of molecular polaritonics. Remarkably, we find that the photorelaxation efficiency is maximized when an optimal trade-off between light-matter coupling strength and photon decay rate is satisfied. This result is in contrast with the common intuition that increasing the quality factor of nanocavities and plasmonic devices improves their performance. Finally, we use a detailed model of a metal nanoparticle to show that the speedup of the uracil relaxation could be observed via coupling with a nanosphere pseudomode, without requiring the implementation of complex nanophotonic structuresThis work has been funded by the
European Research Council through Grants ERC-2016-StG-
714870 (S. Felicetti, J. Feist, and J. Fregoni) and ERC-2015-
CoG-681285 (J. Fregoni, PI Stefano Corni) and by the
Spanish Ministry for Science, Innovation, and Universities -
Agencia Estatal de Investigación through Grants RTI2018-
099737-B-I00, PCI2018-093145 (through the QuantERA
program of the European Commission), and MDM-2014-
0377 (through the Marıá de Maeztu program for Units of
Excellence in R&D). T. Schnappinger and R. de Vivie-Riedle
gratefully acknowledge the DFG Normalverfahren. S. Reiter
gratefully acknowledges financial support by the International Max Planck Research School of Advanced Photon Science
(IMPRS-APS
Making fast photoswitches faster - Using hammett analysis to understand the limit of donor-acceptor approaches for faster hemithioindigo photoswitches
No full textHemithioindigo (HTI) photoswitches have a tremendous potential for biological and supramolecular applications due to their absorptions in the visible-light region in conjunction with ultrafast photoisomerization and high thermal bistability. Rational tailoring of the photophysical properties for a specific application is the key to exploit the full potential of HTIs as photoswitching tools. Herein we use time-resolved absorption spectroscopy and Hammett analysis to discover an unexpected principal limit to the photoisomerization rate for donor-substituted HTIs. By using stationary absorption and fluorescence measurements in combination with theoretical investigations, we offer a detailed mechanistic explanation for the observed rate limit. An alternative way of approaching and possibly even exceeding the maximum rate by multiple donor substitution is demonstrated, which give access to the fastest HTI photoswitch reported to date. An unexpected principal limit to the photoisomerization rate for donor-substituted hemithioindigos (HTIs; see figure) has been discovered; this provides a quantitative estimate for the highest possible photoisomerization rate. A mechanistic explanation for the observed limit is offered together with an alternative way of approaching the maximum rate by multiple donor substitution. This approach gave access to the fastest HTI photoswitch reported to date
Photostability of 4,4′-Dihydroxythioindigo, a Mimetic of Indigo
No full textThe photochemical properties of indigo, a widely used industrial dye, has attracted both experimentalists and theoreticians from the beginning. Especially the high photostability of indigo has been the subject of intensive research. Recently, it was proposed that after photoexcitation an intramolecular proton transfer followed by a nonradiative relaxation to the ground state promote photostability. In indigo the hydrogen bond and the proton transfer occur between the opposing hemiindigo parts. Here, we provide experimental and theoretical evidence that a hydrogen transfer within one hemiindigo or hemithioindigo part is sufficient to attain photostability. This concept can serve as an interesting strategy towards new photostable dyes for the visible part of the spectrum
QDng: A Grid Based Molecular Quantum Dynamics Package
No full text<p>The file contains the source code for the QDng program, which is intended to run under Linux.</p>
Photoinduced B-Cl Bond Fission in Aldehyde-BCl3 Complexes as a Mechanistic Scenario for C-H Bond Activation
No full text: In concert with carbonyl compounds, Lewis acids have been identified as a versatile class of photocatalysts. Thus far, research has focused on activation of the substrate, either by changing its photophysical properties or by modifying its photochemistry. In this work, we expand the established mode of action by demonstrating that UV photoexcitation of a Lewis acid-base complex can lead to homolytic cleavage of a covalent bond in the Lewis acid. In a study on the complex of benzaldehyde and the Lewis acid BCl3, we found evidence for homolytic B-Cl bond cleavage leading to formation of a borylated ketyl radical and a free chlorine atom only hundreds of femtoseconds after excitation. Both time-dependent density functional theory and transient absorption experiments identify a benzaldehyde-BCl2 cation as the dominant species formed on the nanosecond time scale. The experimentally validated B-Cl bond homolysis was synthetically exploited for a BCl3-mediated hydroalkylation reaction of aromatic aldehydes (19 examples, 42-76% yield). It was found that hydrocarbons undergo addition to the C═O double bond via a radical pathway. The photogenerated chlorine radical abstracts a hydrogen atom from the alkane, and the resulting carbon-centered radical either recombines with the borylated ketyl radical or adds to the ground-state aldehyde-BCl3 complex, releasing a chlorine atom. The existence of a radical chain was corroborated by quantum yield measurements and by theory. The photolytic mechanism described here is based on electron transfer between a bound chlorine and an aromatic π-system on the substrate. Thereby, it avoids the use of redox-active transition metals
Temporal and spectral evolution of an interrupted virtual single-photon transition: creation of optical gain and loss
No full textISSN:2100-014XISSN:2101-6275ISSN:2101-627
Mid-Infrared femtosecond filament and three octaves continuum generation in gases
No full textWe report experimental and theoretical results on mid-infrared femtosecond pulse filamentation in different gases. Highly efficient generation of a three-octave-wide spectral continuum in argon, covering the main atmospheric transparency windows, is demonstrated and explained
Optical and x-ray time resolved study of the structural transition in mixed valence manganites
No full textTime resolved optical reflectivity and x-ray diffraction techniques are employed to study the laser-induced structural response in two charge and orbitally ordered manganites. Optical data indicate a non-thermal nature of the laser-triggered phase transition via the disappearance of an optical phonon related to the charge and orbitally ordered phase. The x-ray diffraction measurements on superlattice reflections confirm the non-thermal time scale of the initial step of this phase transition but also show that the complete change of structural symmetry is not instantaneous
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