Fluorinated photoremovable protecting groups: The influence of fluoro substituents on the photo-Favorskii rearrangement

Abstract

To further explore the nature of the photo-Favorskii rearrangement and its commitment to substrate photorelease from p-hydroxyphenacyl (pHP), an array of ten new fluorinated pHP γ-aminobutyric acid (GABA) derivatives was synthesized and photolyzed. The effects of fluorine substitution on the chromophore and the photophysical and photochemical properties of these new chromophores were shown to be derived primarily from the changes in the ground state pKa of the phenolic groups. The quantum yields and rate constants for release are clustered around Φdis = 0.20 ± 0.05 and kr = 8 ± 7 × 107 s-1 (H2O), respectively. The triplet lifetimes of the pHP GABA derivatives were concentrated in the range of 0.4-6.0 ns (H2O). The corresponding deprotonated conjugate bases displayed reduced efficiencies by 50% or more (one exception) and exhibited a weak fluorescence in pH 8.2 buffer. Pump-probe spectroscopy studies have further defined the rates of intersystem crossing and the lifetimes of the reactive triplet state of the fluoro pHP chromophore. © The Royal Society of Chemistry and Owner Societies.