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Issue 20, 2017
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Femtosecond to microsecond observation of the photochemical reaction of 1,2-di(quinolin-2-yl)disulfide with methyl methacrylate

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Abstract

The mechanism of the thiol–ene reaction induced by 330 nm ultraviolet excitation of 1,2-di(quinolin-2-yl)disulfide (QSSQ) in the presence of methyl methacrylate (MMA) is investigated by sub-picosecond to microsecond transient absorption spectroscopy. The measurements, spanning more than seven orders of magnitude of time, directly reveal multiple radical reaction steps. The ground state quinoliene-2-thiyl radical (QS) is formed with a time constant of ∼200 fs by photolysis of QSSQ, followed by (64 ± 1)% decay of the initially formed QS radical because of solvent cage induced geminate recombination and QS dimer formation with a rate coefficient of (3.4 ± 0.2) × 1010 M−1 s−1 in methanol solution. In MMA solution, the carbon centered radical QS-MMA forms with a bimolecular reaction rate coefficient of (2.8 ± 0.2) × 107 M−1 s−1. The distinct infrared band at 1653 cm−1 assigned to the C[double bond, length as m-dash]O stretch mode of the QS-MMA radical decays rapidly in aerated solution, in contrast to observations in a solution purged of O2 by N2 bubbling. This decay is attributed to reaction of the QS-MMA radicals with molecular oxygen, producing peroxy radicals. Kinetic analysis of the intensity of the band at 1653 cm−1 reveals a bimolecular reaction rate coefficient of (3.3 ± 0.3) × 109 M−1 s−1 for the reaction of the QS-MMA radicals with molecular oxygen, and indicates that this reaction step is reversible.

Graphical abstract: Femtosecond to microsecond observation of the photochemical reaction of 1,2-di(quinolin-2-yl)disulfide with methyl methacrylate

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Publication details

The article was received on 20 Mar 2017, accepted on 03 May 2017 and first published on 03 May 2017


Article type: Paper
DOI: 10.1039/C7CP01784G
Citation: Phys. Chem. Chem. Phys., 2017,19, 12981-12991
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    Femtosecond to microsecond observation of the photochemical reaction of 1,2-di(quinolin-2-yl)disulfide with methyl methacrylate

    D. Koyama, P. M. Donaldson and A. J. Orr-Ewing, Phys. Chem. Chem. Phys., 2017, 19, 12981
    DOI: 10.1039/C7CP01784G

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