An acidity scale, [H+]hv, for proton quenching of excited states in aqueous perchloric acid

1989 ◽  
Vol 67 (4) ◽  
pp. 710-719 ◽  
Author(s):  
J. A. Pincock ◽  
P. R. Redden
Keyword(s):  
Excited State ◽  
Activity Coefficient ◽  
Excited States ◽  
Perchloric Acid ◽  
Acidity Function ◽  
Quenching Rate ◽  
Benzyl Alcohols ◽  
Fluorescent Indicator ◽  
Aqueous Perchloric Acid ◽  
Acidity Scale

An acidity scale for excited state protonation kinetics in aqueous perchloric acid has been developed using 1-cyanonaph-thalene as a fluorescent indicator. A comparison of the quenching rate constants obtained using this scale is made with both the more general excess acidity function, X, and the transition state activity coefficient approach. A variety of chromophores were studied including 1- and 2-cyanonaphthalenes, 1- and 2-methoxynaphthalenes, benzyl alcohols, toluenes, benzonitriles, and 2-vinylnaphthalene. Keywords: acidity scale, proton fluorescence quenching.

An acidity scale, [H+]hv, for proton quenching of excited states

1989 ◽  
Vol 67 (2) ◽  
pp. 227-238 ◽  
Author(s):  
J. A. Pincock ◽  
P. R. Redden
Keyword(s):  
Excited State ◽  
Fluorescence Quenching ◽  
Excited States ◽  
Benzyl Alcohols ◽  
Fluorescent Indicator ◽  
Quenching Of Fluorescence ◽  
Acidity Scale

An acidity scale for excited state protonation kinetics in 20% ethanol:80% aqueous sulfuric has been developed using 1-cyano-naphthalene as a fluorescent indicator. The utility of this new scale is demonstrated using the proton quenching of fluorescence of a variety of chromophores. These include 1- and 2-cyanonaphthalenes, 1- and 2-methoxynaphthalenes, benzyl alcohols, toluenes, and 2-vinylnaphthalene. Keywords: acidity scale, fluorescence quenching, excited state basicity.

Construction and Chemometric Analysis of Acidity Function in Perchloric Acid

1999 ◽  
Vol 64 (8) ◽  
pp. 1253-1261 ◽  
Author(s):  
Eva Jirásková ◽  
Jiří Kulhánek ◽  
Taťjana Nevěčná ◽  
Oldřich Pytela
Keyword(s):  
Perchloric Acid ◽  
Regression Coefficient ◽  
Principal Component ◽  
Acidity Function ◽  
First Principle ◽  
Protonated Forms ◽  
Aqueous Perchloric Acid ◽  
High Degree ◽  
Degree Of Similarity ◽  
Indicator Type

Four 2,6-disubstituted anilines with CH3, Cl, and NO2 substituents have been synthesized and, together with four commercial substances of the same type, subjected to spectrophotometry to find the concentration ratios of the protonated and non-protonated forms in aqueous perchloric acid of 0.02-10.55 mol dm-3 concentration. By a procedure devised earlier, the acidity function has been constructed and the pKa values calculated. The Principal Component Analysis was applied to the acidity function obtained and on other eight acidity functions of perchloric acid were taken from literature. It was found that the first principal component explained 99.78% of variability, which indicated high degree of similarity of the said functions irrespective of the indicator type and solvent used. The regression dependences acidity function values on the first principle component are very close, the regression coefficient expressing the measure of sensitivity of the indicator to the acidifying medium. The pKa values obtained agree well with the literature data.

The ketonization of acetophenone enol in concentrated aqueous sulphuric and perchloric acid solutions. Implication on X acidity function correlations of the enolization reaction and determination of the keto–enol equilibrium constant as a function of acidity

1990 ◽  
Vol 68 (10) ◽  
pp. 1653-1656 ◽  
Author(s):  
Y. Chiang ◽  
A. J. Kresge ◽  
R. A. More O'ferrall ◽  
B. A. Murray ◽  
N. P. Schepp ◽  
...  
Keyword(s):  
Sulfuric Acid ◽  
Key Words ◽  
Equilibrium Constant ◽  
Perchloric Acid ◽  
Acidity Function ◽  
Acid Solutions ◽  
Function Correlation ◽  
Aqueous Perchloric Acid ◽  
Sulfuric Acid Solutions

Rates of ketonization of the enol of acetophenone, generated by flash photolytic photohydration of phenylacetylene, were measured in aqueous sulfuric and perchloric acid solutions over the concentration range 1–50 wt.% acid; rates of enolization of acetophenone, monitored by bromine scavenging, were also measured in aqueous perchloric acid solutions over the same concentration range. The results suggest that the curvature observed in a previous X acidity function correlation of the rate of enolization in sulfuric acid solutions was an artifact produced by insufficiently efficient scavenging, and that introduction of the activity of water in the correlating expression, used previously to eliminate the curvature and believed to reflect covalent involvement of water in the enolization reaction, is unnecessary. The present results also show that the keto–enol equilibrium constant for acetophenone decreases with increasing acidity in these concentrated sulfuric and perchloric acid solutions. Key words: acetophenone, enolization, ketonization, keto–enol equilibrium, concentrated acid solutions.

Carbon protonation of some phenylynamines in concentrated aqueous perchloric acid solution. Lowering of the upper limit for the pKa of phenylynammonium ions

1996 ◽  
Vol 74 (7) ◽  
pp. 1373-1376 ◽  
Author(s):  
A.J. Kresge ◽  
S.W. Paine
Keyword(s):  
Acid Solution ◽  
Perchloric Acid ◽  
Rate Theory ◽  
Acidity Function ◽  
Perchloric Acid Solution ◽  
Hydronium Ion ◽  
Dilute Acid Solution ◽  
Saturated Compound ◽  
Initial States ◽  
Aqueous Perchloric Acid

Rates of carbon protonation of five phenylynamines (PhC≡CNH2, PhC≡CNHiPr, PhC=CNHC6F5, PhC≡CN(CH2CH2CN)2, and PhC≡CNMeC6F5) were determined in concentrated aqueous perchloric acid solution and the data were analyzed by the Cox–Yates method using the X0 acidity function. The extrapolated hydronium-ion catalytic coefficients so obtained are consistent with values measured directly in dilute acid solution, and the slopes of the Cox-Yates plots are similar to predictions made with the aid of Marcus rate theory for reactions originating from free ynamine initial states but unlike those predicted for reactions starting from nitrogen-protonated ynammonium ion initial states. This shows that none of these phenylynamines are protonated in even the most acidic solutions used (4 M) and sets new upper limits as low as pKa ≤ −3.1 for the conjugate acids of these ynamines. Comparison of the pKa limit for PhC≡CNH3+ with a literature value for the corresponding saturated compound, PhCH2CH2NH3+, gives a base-weakening effect for the phenylethynyl group of at least 12.5 pK units. Key words: acetylenic amines, concentrated acids, X0 excess acidity scale, Cox-Yates method, Marcus rate theory.

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>

Participation of 19-substituents in electrophilic additions to 6,7-unsaturated 5α-cholestane and B-homo 5α-cholestane derivatives; A case of competition between the participation of an ambident neighboring group and external nucleophile attack

1980 ◽  
Vol 45 (2) ◽  
pp. 559-583 ◽  
Author(s):  
Pavel Kočovský ◽  
Ladislav Kohout ◽  
Václav Černý
Keyword(s):  
Perchloric Acid ◽  
Hydrobromic Acid ◽  
Cyclic Ether ◽  
Cyclic Ethers ◽  
Neighboring Group ◽  
Acid Cleavage ◽  
Neighbouring Group Participation ◽  
Aqueous Perchloric Acid ◽  
The Difference ◽  
Electrophilic Additions

Hypobromous acid action upon the 6,7-unsaturated 19-substituted 5α-cholestans Va-Vc results in the formation of two types of products, the cyclic ethers IX as products of 5(O)n participation of the 19-substituent, and the bromohydrins X. All these compounds are formed from the 6α,7α-bromonium ions Va'-Vc'. Under the same conditions the B-homo-5α-cholestane derivatives VIIa-VIIc afforded solely the cyclic ethers XIV as products of 5(O)n participation of the 19-substituent in the cleavage of the bromonium ions VIIa'-VIIc'. Acid cleavage of the 6α,7α-epoxides VIb and VIc with aqueous perchloric acid or hydrobromic acid gave two types of products, i.e. the cyclic ethers XI and the diols XII or bromohydrines XIII. The cyclic ethers XI arise by 5(O)n participation of the 19-substituent. The B-homo-6α, 7α-epoxide VIIIc on cleavage with aqueous perchloric acid have solely the cyclic ether XVc and by treatment with hydrobromic acid VIIIc afforded the mixture of XVc, as the main product, and of the bromohydrin XVIc. Discussed is the similarity of the bromonium ion cleavage with the fission of the corresponding epoxides, the mechanism of these reactions and the difference in the behaviour of the isomeric olefins Ia-c, IIIa-c, Va-c and VIIa-c and epoxides IIb,c, IVb,c, VIb,c and VIIIb,c. The competition between ambident neighbouring group participation and external nucleophile attack is discussed as well as the dependence of the products ratio on the nucleophilicity of the attacking species.

scholarly journals Ground- and excited-state characteristics in photovoltaic polymer N2200

RSC Advances ◽  
2021 ◽  
Author(s):  
Guanzhao Wen ◽  
Xianshao Zou ◽  
Rong Hu ◽  
Jun Peng ◽  
Zhifeng Chen ◽  
...  
Keyword(s):  
Density Functional Theory ◽  
Excited State ◽  
Steady State ◽  
Excited States ◽  
Density Functional ◽  
Density Functional Theory Calculations ◽  
Time Dependent ◽  
Functional Theory ◽  
Time Resolved ◽  
Dependent Density

Ground- and excited-states properties of N2200 have been studied by steady-state and time-resolved spectroscopies as well as time-dependent density functional theory calculations.

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