Unusual concentration dependence of the photoisomerization reaction in donor–acceptor Stenhouse adducts. Issue 6 (15th May 2019)

• Record Type: Journal Article
• Authors: Lui, Brandon F.; Tierce, Nathan T.; Tong, Fei; Sroda, Miranda M.; Lu, Hao; Read de Alaniz, Javier; Bardeen, Christopher J.
• Is Part Of: Photochemical & photobiological sciences. Volume 18:Issue 6(2019)
• Page Start: 1587
• Page End: 1595
• Publication Date: 2019-05-15
• Subjects: Photochemistry -- Periodicals; Photobiology -- Periodicals; 541.35
• DOI: 10.1039/c9pp00130a
• Languages: English
• ISSNs: 1474-905X

Abstract

Abstract : The isomerization rates of a photochromic donor–acceptor Stenhouse adduct depend on concentration. The net photoisomerization rate decreases with increasing concentration in liquids and polymers. Abstract : Donor–acceptor Stenhouse adducts comprise a new class of reversible photochromic molecules that absorb in the visible and near-infrared spectral regions. Unimolecular photoisomerization reactions are usually assumed to be insensitive to photochrome density, at least up to millimolar concentrations. In this paper, the photoisomerization kinetics of a third-generation donor–acceptor Stenhouse adduct molecule (denotedDASA ) are examined over a range of concentrations.DASA switches efficiently at micromolar concentrations in both liquid solution and in polymers, but as the photochrome concentration is increased there is a dramatic inhibition of the photoisomerization. A kinetic study of both the reactant and photoproduct decays at varying concentrations and in different hosts indicates that the forward photoisomerization and the thermal backward reaction can change by factors of 20 or more depending onDASA concentration. Femtosecond transient absorption experiments show that the initial cis → trans step of the isomerization is not affected by concentration. It is hypothesized that long-range coulombic interactions interfere with the ground state electrocyclization stage of the isomerization, which is unique to theDASA family of photochromes. The physical origin of the inhibition of photoswitching at high photochrome concentrations must be understood if theDASA class of molecules is to be used for applications that require high photochrome concentrations, including photomechanical actuation.