scholarly journals Hole-Mediated PhotoRedox Catalysis: Tris(p-Substituted)biarylaminium Radical Cations as Tunable, Precomplexing and Potent Photooxidants

2020 ◽  
Author(s):  
Shangze Wu ◽  
Jonas Zurauskas ◽  
Michal Domanski ◽  
Patrick Hitzfeld ◽  
Valeria Butera ◽  
...  
Keyword(s):  
Cyclic Voltammetry ◽  
Excited State ◽  
Excited States ◽  
Organic Molecules ◽  
Radical Cations ◽  
Single Electron Transfer ◽  
Photoredox Catalysis ◽  
Small Organic Molecules ◽  
Fundamental Limitations ◽  
Ion Species

<p>Electrochemically-mediated Photoredox Catalysis emerged as a powerful synthetic technique in recent years, overcoming fundamental limitations of electrochemistry and photoredox catalysis in the single electron transfer activation of small organic molecules. However, the mechanism of how photoexcited radical ion species with ultrashort (picosecond-order) lifetimes could ever undergo productive photochemistry has eluded synthetic chemists. We report tri(<i>para</i>-substituted)biarylamines as a tunable class of electroactivated photocatalysts that become superoxidants in their photoexcited states, even able to oxidize molecules (such as dichlorobenzene and trifluorotoluene) beyond the solvent window limits of cyclic voltammetry. Furthermore, we demonstrate that precomplexation not only permits the excited state photochemistry of tris(<i>para</i>-substituted)biarylaminium cations, but enables and rationalizes the surprising photochemistry of their <i>higher-order</i> doublet (D<i><sub>n</sub></i>) excited states.</p>

scholarly journals Hole-Mediated PhotoRedox Catalysis: Tris(p-Substituted)biarylaminium Radical Cations as Tunable, Precomplexing and Potent Photooxidants

2020 ◽  
Author(s):  
Shangze Wu ◽  
Jonas Zurauskas ◽  
Michal Domanski ◽  
Patrick Hitzfeld ◽  
Valeria Butera ◽  
...  
Keyword(s):  
Cyclic Voltammetry ◽  
Excited State ◽  
Excited States ◽  
Organic Molecules ◽  
Radical Cations ◽  
Single Electron Transfer ◽  
Photoredox Catalysis ◽  
Small Organic Molecules ◽  
Fundamental Limitations ◽  
Ion Species

<p>Electrochemically-mediated Photoredox Catalysis emerged as a powerful synthetic technique in recent years, overcoming fundamental limitations of electrochemistry and photoredox catalysis in the single electron transfer activation of small organic molecules. However, the mechanism of how photoexcited radical ion species with ultrashort (picosecond-order) lifetimes could ever undergo productive photochemistry has eluded synthetic chemists. We report tri(<i>para</i>-substituted)biarylamines as a tunable class of electroactivated photocatalysts that become superoxidants in their photoexcited states, even able to oxidize molecules (such as dichlorobenzene and trifluorotoluene) beyond the solvent window limits of cyclic voltammetry. Furthermore, we demonstrate that precomplexation not only permits the excited state photochemistry of tris(<i>para</i>-substituted)biarylaminium cations, but enables and rationalizes the surprising photochemistry of their <i>higher-order</i> doublet (D<i><sub>n</sub></i>) excited states.</p>

MNDO and AM1 study of molecular geometries in excited states

1990 ◽  
Vol 55 (6) ◽  
pp. 1399-1403 ◽  
Author(s):  
Peter Ertl
Keyword(s):  
Excited State ◽  
Excited States ◽  
Configuration Interaction ◽  
Organic Molecules ◽  
Semiempirical Methods ◽  
Better Than

Geometries of the singlet excited states of series of organic molecules have been calculated using MNDO and AM1 semiempirical methods with limited configuration interaction. Changes in molecular geometries after excitation are reproduced reasonably well, with AM1 being superior to MNDO, which in some cases fails. Molecules having biradical-like character in excited state are described better than classical ones.

Influence of Additives on the Speciation, Morphology, and Nanocrystallinity of Aluminium Electrodeposition

2012 ◽  
Vol 65 (11) ◽  
pp. 1523 ◽  
Author(s):  
Lian Liu ◽  
Xingmei Lu ◽  
Yingjun Cai ◽  
Yong Zheng ◽  
Suojiang Zhang
Keyword(s):  
Cyclic Voltammetry ◽  
Organic Molecules ◽  
Analytical Techniques ◽  
Separation Process ◽  
X Ray Diffraction ◽  
Alkali Metal Chlorides ◽  
Metal Chlorides ◽  
Small Organic Molecules ◽  
X Ray ◽  
Scanning Electron

The effects of various additives, including alkali metal chlorides, rare earth chlorides, small organic molecules, and surfactants on the electrodeposition of aluminium were investigated. The analytical techniques of cyclic voltammetry, potentiostatic coulometry, scanning electron microscope, and X-ray diffraction were applied to determine the speciation, morphology, and nanocrystallinity. It was found that additives significantly influence the morphology and grain parameters of the aluminium deposits. Inorganic additives and macromolecular surfactants play a prominent role in altering the speciation of aluminium. Small organic molecules (including surfactants) with simple structures have almost no effect on the aluminium separation process, but have a role in densification and homogenisation. In addition, the grain size can be adjusted after adding various additives, and then nanocrystallinity can be achieved. In conclusion, the effect of additive on the aluminium deposit can be predicted by cyclic voltammetry, which is a clue for smart-design on technological conditions of aluminium electrodeposition.

Spin-Forbidden Excitation Enables Infrared Photoredox Catalysis

2020 ◽  
Author(s):  
Tomislav Rovis ◽  
Benjamin D. Ravetz ◽  
Nicholas E. S. Tay ◽  
Candice Joe ◽  
Melda Sezen-Edmonds ◽  
...  
Keyword(s):  
Excited State ◽  
Ground State ◽  
Intersystem Crossing ◽  
Photoredox Catalysis ◽  
Infrared Irradiation ◽  
Triplet Excitation ◽  
New Family ◽  
Ir Light

We describe a new family of catalysts that undergo direct ground state singlet to excited state triplet excitation with IR light, leading to photoredox catalysis without the energy waste associated with intersystem crossing. The finding allows a mole scale reaction in batch using infrared irradiation.

QUBEKit: Automating the Derivation of Force Field Parameters from Quantum Mechanics

2019 ◽  
Author(s):  
Joshua Horton ◽  
Alice Allen ◽  
Leela Dodda ◽  
Daniel Cole
Keyword(s):  
Quantum Mechanics ◽  
Force Field ◽  
Organic Molecules ◽  
Force Fields ◽  
Liquid Density ◽  
Small Organic Molecules ◽  
Automated Generation ◽  
Energy Of Hydration ◽  
Novel Method ◽  
Force Field Parameters

<div><div><div><p>Modern molecular mechanics force fields are widely used for modelling the dynamics and interactions of small organic molecules using libraries of transferable force field parameters. For molecules outside the training set, parameters may be missing or inaccurate, and in these cases, it may be preferable to derive molecule-specific parameters. Here we present an intuitive parameter derivation toolkit, QUBEKit (QUantum mechanical BEspoke Kit), which enables the automated generation of system-specific small molecule force field parameters directly from quantum mechanics. QUBEKit is written in python and combines the latest QM parameter derivation methodologies with a novel method for deriving the positions and charges of off-center virtual sites. As a proof of concept, we have re-derived a complete set of parameters for 109 small organic molecules, and assessed the accuracy by comparing computed liquid properties with experiment. QUBEKit gives highly competitive results when compared to standard transferable force fields, with mean unsigned errors of 0.024 g/cm3, 0.79 kcal/mol and 1.17 kcal/mol for the liquid density, heat of vaporization and free energy of hydration respectively. This indicates that the derived parameters are suitable for molecular modelling applications, including computer-aided drug design.</p></div></div></div>

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>

The Malleable Excited States of Benzothiadiazole Dyes and Investigation of their Potential for Photochemical Control

2019 ◽  
Author(s):  
Caroline C. Warner ◽  
andrea thooft ◽  
Bryan J. Lampkin ◽  
selin demirci ◽  
Brett VanVeller
Keyword(s):  
Excited State ◽  
Excited States ◽  
Polar Solvent ◽  
Nonpolar Solvent ◽  
Photochemical Degradation ◽  
Solvent Lead ◽  
Environmentally Sensitive

<p>A strategy to control the efficiency of a photocleavage reaction based on changing the nature of the excited state is presented. A novel class of photoactive compounds has been synthesized by combining the classical o-nitrobenzyl scaffold with an environmentally sensitive dye, 4-amino-nitrobenzothiazole. Irradiation in a polar solvent lead to an excited state that is inoperative for photochemistry whereas excitation in a nonpolar solvent lead to an excited state that is photochemically active. A photochemical degradation appears to be the preferred process in contrast to the intended photocleavage process.</p>

Excited State Tracking During the Relaxation of Coordination Compounds

2018 ◽  
Author(s):  
Juan Sanz García ◽  
Martial Boggio-Pasqua ◽  
Ilaria Ciofini ◽  
Marco Campetella
Keyword(s):  
Excited State ◽  
Excited States ◽  
Potential Energy Surfaces ◽  
Photochemical Reactions ◽  
Complex Nature ◽  
Electronic Excited States ◽  
Ruthenium Nitrosyl ◽  
State Tracking ◽  
Energy Surfaces ◽  
Electronic Wavefunction

<div>The ability to locate minima on electronic excited states (ESs) potential energy surfaces (PESs) both in the case of bright and dark states is crucial for a full understanding of photochemical reactions. This task has become a standard practice for small- to medium-sized organic chromophores thanks to the constant developments in the field of computational photochemistry. However, this remains a very challenging effort when it comes to the optimization of ESs of transition metal complexes (TMCs), not only due to the presence of several electronic excited states close in energy, but also due to the complex nature of the excited states involved. In this article, we present a simple yet powerful method to follow an excited state of interest during a structural optimization in the case of TMC, based on the use of a compact hole-particle representation of the electronic transition, namely the natural transition orbitals (NTOs). State tracking using NTOs is unambiguously accomplished by computing the mono-electronic wavefunction overlap between consecutive steps of the optimization. Here, we demonstrate that this simple but robust procedure works not only in the case of the cytosine but also in the case of the ES optimization of a ruthenium-nitrosyl complex which is very problematic with standard approaches.</div>

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