Photocatalysis and self-catalyzed photobleaching with covalently-linked chromophore-quencher conjugates built around BOPHY?

Photochemical & Photobiological Sciences Pub Date: 2018-04-25 DOI: 10.1039/C8PP00162F

Abstract

Two Chromophore-Quencher Conjugates (CQCs) have been synthesized by covalent attachment of the anti-oxidant dibutylated-hydroxytoluene (BHT) to a pyrrole-BF2 chromophore (BOPHY) in an effort to protect the latter against photofading. In fluid solution, light-induced intramolecular charge transfer is favoured in polar solvents and helps to inhibit photo-bleaching of the chromophore. The rate of photo-fading, which scales with the number of BHT residues, is zero-order in polar solvents but shows a linear dependence on the number of absorbed photons. The zero-order rate constant shows an inverse correlation with the fluorescence quantum yield measured in the same solvent. Photo-bleaching in benzonitrile involves autocatalysis while reaction in cyclohexane shows an unexpected stoichiometry. NMR spectroscopy indicates initial damage takes place at the BHT unit and allows identification of a reactive hydroperoxide as being the primary product. In the presence of an adventitious substrate, this hydroperoxide is a photocatalyst for amide formation under mild conditions.

Graphical abstract: Photocatalysis and self-catalyzed photobleaching with covalently-linked chromophore-quencher conjugates built around BOPHY
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