Photocyanation of 3,4-dimethoxy-1-nitrobenzene. A quantitative study

1986 ◽  
Vol 51 (2) ◽  
pp. 358-367 ◽  
Author(s):  
Petr Kuzmič ◽  
Milan Souček
Keyword(s):  
Quantum Yield ◽  
Quantitative Study ◽  
Rate Constant ◽  
Potassium Cyanide ◽  
Intersystem Crossing ◽  
Excited Triplet ◽  
Cyanide Anion ◽  
Tert Butanol ◽  
Diffusion Controlled ◽  
Triplet Lifetime

UV photolysis (365 nm) of 3,4-dimethoxy-1-nitrobenzene in the presence of potassium cyanide leading to 3-cyano-4-methoxy-1-nitrobenzene was subjected to a quantitative photokinetic study. The reaction exhibits a second order kinetics with respect to the nucleophile and is effectively quenched by molecular oxygen as well as 2,4-hexadienoic acid. The excited triplet lifetime of 0.9 microseconds was determined on the basis of the dependence of quantum yield on the nucleophile and quencher concentrations in 50% aqueous tert-butanol. The quantum yield of intersystem crossing is at least 0.38 in the same solvent; bimolecular rate constant for the interaction of triplet 3,4-dimethoxy-1-nitrobenzene with cyanide anion has the value of 5.6 . 108 l . mol-1s-1, which is approximately one half of the rate constant for diffusion controlled quenching. Quantum yield of the reaction is strongly dependent on the water content in mixtures with tert-butanol and increases from 0.04 in water to 0.68 in 88% tert-butanol.

scholarly journals Picosecond Laser Study of Thioindigoid Dyes Photoisomerization

1984 ◽  
Vol 4 (1-6) ◽  
pp. 121-128 ◽  
Author(s):  
S. A. Krysanov ◽  
M. V. Alfimov
Keyword(s):  
Quantum Yield ◽  
Rate Constant ◽  
Time Domain ◽  
Singlet State ◽  
Picosecond Laser ◽  
Intersystem Crossing ◽  
Transient Species ◽  
Triplet Mechanism ◽  
The Time Domain ◽  
Cis Isomer

The transient species in the trans ⇌ cis photoisomerization of the perinaphto–thioindigoid dye were identified by picosecond laser spectroscopy in the time domain 10 ps–5 ns. An excitation of the trans isomer with a 6 ps, 528 nm pulse to the singlet state S1 (the peak of S′n ← S1 absorption at 700 nm) results in the intersystem crossing S1 ⇝ T1 (the peak of Tn ← T1 absorption at 730 nm) with the quantum yield of 0.7 and rate constant (1.4 ± 0.3)· 109s−1. An excitation of the cis isomer results also in the intersystem crossing (the peak of Tn> ← T1 absorption at 670 nm) with the rate constant (3.7 ± 1.2)· 1010s−1. The triplet mechanism of the photoisomerization in the both directions is proposed.

The photochemistry of 2-furaldehyde vapour. I. Photophysical processes: phosphorescence excited in the π* ← n transition

1976 ◽  
Vol 54 (19) ◽  
pp. 3089-3094 ◽  
Author(s):  
A. Gandini ◽  
P. A. Hackett ◽  
R. A. Back
Keyword(s):  
Quantum Yield ◽  
Pressure Dependence ◽  
Intersystem Crossing ◽  
Absorption Bands ◽  
Excited Triplet ◽  
Photophysical Processes

A search was made for emission from 2-furaldehyde, following excitation in the first two absorption bands. Only phosphorescence from the 3nπ* state was observed. The pressure dependence of the lifetime and quantum yield of this emission was determined, as well as that of the quantum yield of intersystem crossing. A mechanism involving self-quenching of excited triplet 2-furaldehyde is proposed.

Joining of Ti3SiC2 with Ti–6Al–4V Alloy

2002 ◽  
Vol 17 (1) ◽  
pp. 52-59 ◽  
Author(s):  
N.F. Gao ◽  
Y. Miyamoto
Keyword(s):  
Solid State ◽  
Rate Constant ◽  
Liquid State ◽  
Parabolic Rate Constant ◽  
Diffusion Path ◽  
Solid State Diffusion ◽  
Diffusion Controlled ◽  
State Diffusion ◽  
Rate Controlled ◽  
Higher Temperature

The joining of a Ti3SiC2 ceramic with a Ti–6Al–4V alloy was carried out at the temperature range of 1200–1400 °C for 15 min to 4 h in a vacuum. The total diffusion path of joining was determined to be Ti3SiC2/Ti5Si3Cx/Ti5Si3Cx + TiCx/TiCx/Ti. The reaction was rate controlled by the solid-state diffusion below 1350 °C and turned to the liquid-state diffusion controlled with a dramatic increase of parabolic rate constant Kp when the temperature exceeded 1350 °C. The TiCx tended to grow at the boundarywith the Ti–6Al–4V alloy at a higher temperature and longer holding time. TheTi3SiC2/Ti–6Al–4V joint is expected to be applied to implant materials.

Die Reaktionen chlorierter Äthylene mit hydratisierten Elektronen und OH-Radikalen in wäßriger Lösung / The Reaction of Chlorinated Ethylenes with Hydrated Electrons and OH-Radicals in Aqueous Solution

1971 ◽  
Vol 26 (11) ◽  
pp. 1108-1116 ◽  
Author(s):  
R. Köster ◽  
K.-D. Asmus
Keyword(s):  
Rate Constant ◽  
Oh Radicals ◽  
Capture Process ◽  
Chlorinated Ethylenes ◽  
Diffusion Controlled ◽  
Hydrated Electrons ◽  
Cl Atoms ◽  
Type Radical ◽  
Cl Atom ◽  
Steric Hinderance

The reactions of chlorinated ethylenes with hydrated electrons and OH radicals have been investigated by using the method of pulse radiolysis. In addition γ-ray experiments were carried out. The reduction of the solutes occurs via a dissoziation electron capture process. The rate constant for the reaction of eaq⊖ with the more chlorinated compounds is essentially diffusion controlled (k= (1 - 2×1010 l-mole-1 sec-1). Vinylchloride and 1,2-trans-dichloroethylene react more slowly. This can be related to the higher stability of the C-Cl bond in these compounds.Hydroxyl radicals add to the C=C double bond of the chlorinated ethylenes. The rate constant for the reaction with vinylchloride was determined to 7.1 × 109 1 · mole-1 sec-1, and decreases with increasing degree of chlorination of the ethylenes. This effect is explained by the decreasing electron density on the C-atoms and steric hinderance. The hydroxyl radical always adds to the C-atom carrying the smallest number of Cl-atoms. In its reaction with 1,2-dichloro-, trichloro- and tetrachloroethylene a radical is produced with an OH group and a Cl-atom on the same C-atom. It eliminates HCl to form a C=O bond with k>7 × 105 sec-1. The type radical produced in this reaction has an optical absorption in the near UV (ε265 nm = (1-3)×103 1 · mole-1 cm-1).The OH radical addition products of vinylchloride and 1,1-dichloroethylene do not eliminate HCl and have no absorption in the visible and near UV.

Diffusion‐controlled reactions: Upper bounds on the effective rate constant

1991 ◽  
Vol 94 (12) ◽  
pp. 7967-7971 ◽  
Author(s):  
J. Blawzdziewicz ◽  
G. Szamel ◽  
H. Van Beijeren
Keyword(s):  
Rate Constant ◽  
Effective Rate Constant ◽  
Effective Rate ◽  
Upper Bounds ◽  
Diffusion Controlled

IMPROVEMENT OF THE PHOTOPHYSICAL PARAMETERS OF ZINC OCTACARBOXY PHTHALOCYANINE UPON CONJUGATION TO MAGNETIC NANOPARTICLES

2013 ◽  
Vol 12 (02) ◽  
pp. 1350010 ◽  
Author(s):  
PHILLIMON MODISHA ◽  
EDITH ANTUNES ◽  
JOHN MACK ◽  
TEBELLO NYOKONG
Keyword(s):  
Magnetic Nanoparticles ◽  
Quantum Yield ◽  
Singlet Oxygen ◽  
Amide Bond ◽  
Amino Group ◽  
Covalent Linkage ◽  
Transmission Electron ◽  
Photophysical Parameters ◽  
Photophysical Behavior ◽  
Triplet Lifetime

Magnetic nanoparticles (MNPs) comprising magnetite (Fe3O4) were functionalized with 3-aminopropyl-triethoxysilane forming amino functionalized magnetite nanoparticles (AMNPs). The amino group allows for conjugation with zinc octacarboxyphthalocyanine ( ZnOCPc ) via the carboxyl group to form an amide bond. Transmission electron microscopy showed a change in morphology after conjugation. The covalent linkage of AMNPs to ZnOCPc has shown improvements in the photophysical behavior of the Pc in the presence of the MNP, increasing the triplet quantum yield (ΦT), singlet oxygen quantum yield (ΦΔ), triplet lifetime (τT) and singlet oxygen lifetime (τΔ) of the ZnOCPc and thus improving the efficiency of the ZnOCPc as a photosensitizer.

scholarly journals Mechanistic Investigations of an α-Aminoarylation Photoredox Reaction

2021 ◽  
Author(s):  
Bernard Stevenson ◽  
Ethan Spielvogel ◽  
Emily Loiaconi ◽  
Victor M. Wambua ◽  
Roman Nakhamiyayev ◽  
...  
Keyword(s):  
Quantum Yield ◽  
Absorption Spectroscopy ◽  
Rate Constant ◽  
Kinetic Modeling ◽  
Rate Constants ◽  
Transient Absorption ◽  
Coupling Reaction ◽  
Time Dependent ◽  
Transient Absorption Spectroscopy ◽  
Mechanistic Investigations

We present time-dependent percent and quantum yield measurements of a photoredox-catalyzed coupling reaction between 1,4-dicyanobenzene and N-phenylpyrrolidine. We also use transient absorption spectroscopy to examine the kinetics within the reaction and use kinetic modeling to extract rate constants and predict how changes in rate constant will impact the quantum yield.

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