Solvent partitioning in fluorescent polydimethylsiloxane networks

Abstract

End-linked polydimethylsiloxane networks have been synthesized with 5-dimethylaminonaphthalene-1-sulfonamide (dansyl) chromophores covalently bound to trifunctional silane cross-linkers. The solvatochromic behaviour of the dansyl-tagged cross-linkers, dissolved in solvents and bound in swollen networks, has been investigated. The spectral shifts in one-component solvents are characteristic of the dansyl probe and are explained in terms of dielectric solvent relaxation and solvophobic effects. In binary solvent mixtures, analogous to the swollen network, preferential solvation of the probe by the more polar solvent is observed and explained using a model for dielectric enrichment. Solvent partitioning in swollen networks is stronger than in the binary solutions and is attributed to a combination of dipoledipole interactions and configurational restriction effects. Owing to large spectral shifts measured from networks swollen with small amounts of alcohols, this material may find application as a transducing element in a fibre-optic alcohol sensor.