Cation Complexation, Photochromism, and Aggregation of Copolymers Carrying Crown Ether and Spirobenzopyran Moieties at the Side Chains

Methacrylate monomers containing monoaza-12-crown-4 and spirobenzopyran moieties were copolymerized to obtain polymers carrying their moieties at the side chains. The crown ether-spiropyran polymers can bind alkali metal ions with their crown ether moiety in the selectivity order of Na^+ > K^+ > Li^+. The spirobenzopyran moiety, on the other hand, undergoes UV-light-induced isomerization from its spiropyran to the merocyanine form, leading to merocyanine aggregate formation. The metal-ion complexation of the crown ether moiety enhanced interpolymer merocyanine aggregation by extending the polymer chain on the basis of the electrostatic repulsion between the complexed metal ions. Thus, tetrahydrofuran solutions of a crown ether-spiropyran copolymer with 1 : 1 composition of the moieties led to significant polymer precipitation on UV irradiation in the presence of an alkali metal ion, especially Li^+. The photochromism and aggregate formation were studied in detail by absorption and fluorescence spectrometry and by light scattering measurements.