Solvent and Temperature Effects on Polymer-Coated Glass Fibers. Fluorescence of the Dansyl Moiety

Abstract

E-type glass fibers were coated with poly(γ-aminopropyltriethoxysilane), treating them with a 1% (v/v) monomer aqueous solution. The fibers were labeled with a dansyl-sulfonamide conjugate by reaction of acetonitrile solutions of dansyl chloride with the amine groups immobilized on the glass fiber surface. Interactions of the labeled coating polymer with solvents of different polarities were estimated by measurements of the fluorescence band shifts of the label. It was found that for aprotic solvents, the solvent dipolar coupling relaxation mechanism is dominated by thermodynamic interactions of the solvent with the polymer matrix, while for protic solvents this mechanism is dominated by specific interactions between solvent molecules and the excited state of the chromophore. Different experimental excited-state dipole moments were obtained for nonpolar and polar solvents (μ^* _NP = 7.2 ± 1.6 D, μ^* _P = 11.9 ± 1.5 D). Using the AM1 method, excited-state dipole moments for the first and second singlets were calculated and it was concluded that μ^* _NP ≃ 〈μ^*2 ₁〉^1/2 and μ^* _P ≃ 〈μ^*2 ₂〉^1/2. Accordingly, neither the glass support nor the coating polar influence the excited-state properties of dansyl. The temperature dependence of dansyl emission allows the determination of the relaxation temperature of the coating polymer, which was estimated as 175 K for the coating used.