Photo‐Fries Rearrangement in Polymeric Media: An Investigation on Fully Aromatic Esters Containing the Naphthyl Chromophore

The present paper deals with the photo-Fries rearrangement of fully aromatic esters in polymeric media. Low molecular weight aryl esters bearing the 1-naphthyl chromophore were investigated with respect to their photochemical reactivity and the yield of hydroxyketones as the photo-Fries rearrangement product. In particular, the phenyl, 4-methylphenyl and 1-naphthyl ester of 1-naphthoic acid, as well as benzoic acid, 1-naphthyl ester were dissolved in a polysiloxane matrix and exposed to 313 nm UV light. The progress of the photoreaction was assessed by quantitative FT-IR spectroscopy. Both 1-naphthoic acid, phenyl ester and benzoic acid, 1-naphthyl ester underwent the photoreaction upon 313 nm irradiation. This indicates that in these fully aromatic esters, the initial C-O bond scission also occurs upon selective photoexcitation of the acyl unit in the molecule. It was found that phenyl and 4-methylphenyl esters of 1-naphthoic acid gave the highest yields of hydroxyketone when irradiated in polymer matrix. Based upon these results, a photoreactive monomer was designed which contains naphthoic acid, phenyl ester units attached to a norbornene ring. This monomer was then polymerized by ring opening metathesis polymerization (ROMP). The polymer showed a high yield in the photo-Fries reaction upon 313 nm illumination. Moreover, a large increase in the refractive index (Δn up to +0.043 at λ = 370 nm) was observed which makes this polymer interesting for optical applications (e.g., waveguiding and diffractive optics).