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

Abstract

AbstractThe 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).magnified image