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The Missing Piece: Concentration Dependence of Donor‐Acceptor Stenhouse Adduct (DASA) Reactivity
Author(s) -
Alves Jessica,
Wiedbrauk Sandra,
BarnerKowollik Christopher,
Blinco James P.
Publication year - 2021
Publication title -
chemphotochem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.13
H-Index - 18
ISSN - 2367-0932
DOI - 10.1002/cptc.202100056
Subject(s) - adduct , thiol , chemistry , reactivity (psychology) , michael reaction , isomerization , kinetics , photochemistry , reaction rate constant , acceptor , catalysis , organic chemistry , medicine , physics , alternative medicine , pathology , quantum mechanics , condensed matter physics
Donor‐Acceptor Stenhouse Adducts (DASAs) are molecular photoswitches that reversibly isomerize from a linear to a cyclized form upon visible light irradiation. In the cyclized form, these molecules selectively react with a thiol in a thiol‐Michael addition. Driven by the complexity of the switching mechanism and chemical properties of DASAs, the effect of concentration (ranging from 1 to 5 mM DASA) on the thiol‐Michael addition was investigated. We find that the rate limiting step in the reaction is the photochemically induced DASA isomerization, as higher concentrations of thiol do not alter the rate at which the thiol‐Michael adduct (TMA) is formed. Moreover, the kinetics of the product formation were found to be more significantly affected by irradiation at higher concentrations. In two distinct scenarios, where either the concentration or the molar equivalence of the reaction partner was kept constant, the TMA was found to be more efficiently formed under irradiation at higher concentrations. These findings indicate that the DASA reactivity towards thiol‐Michael reactions appear to be equilibrium‐driven at lower concentrations and light‐driven at higher concentrations.