Fluorescence and Singlet Energy Migration in Conformationally Restrained Acrylate Polymers Bearing Pendant Chromophores

Abstract

Fluorescence and singlet energy migration can be studied in chromophore-appended polyacrylates in which conformationally restricted ring structures in the polymer backbone prevent excimer formation. Specifically, two substituted α-methylene-γ-butyrolactones (1a bearing a naphthyl group and 1b bearing a phenanthryl group) and a naphthyl-substituted diethyl 2,6-dimethyleneheptanedioate (2) yield linear polymers with five-membered rings fixed perpendicular to the main chain (poly(1)) or cyclopolymers with six-membered rings in the main chain (poly(2)) upon radical or group transfer polymerization. 4-Methyl-4-(2-naphthyl)butyrolactone (3a), 4-methyl-4-(3-phenanthryl)butyrolactone (3b), and 1-(1-naphthylmethoxycarbonyl)-1-(ethoxycarbonyl)cyclohexane (4) were prepared as spectroscopic models for these polymers. No evidence for excimer emission could be seen in poly(1a) or poly(1b), but poly(2) exhibited weak excimer emission. Defects in the polymer structure of poly(2) correlate with observed sites for excimer formation. Steady-state fluorescence quenching experiments by CCl 4 demonstrate that singlet energy migration occurs intramolecularly along these polymer chains.