Photophysical properties of thionine and phenosafranine dyes covalently bound to macromolecules

Abstract

Thionine dye was condensed with poly(acrylamidoglycolic acid) (P(AGA)) and poly (methylolacrylamide) (P(MAAM)). Phenosafranine dye was condensed with P(MAAM). The emission, absorption and fluorescence excitation spectra of thionine dye covelently linked to P(AGA) were studied. Electrochemical reduction of P (AGA)-bound thionine shows that both monomeric thionine and non-reducible thionine are bound to the macromolecule; bound non-reducible thionine is non-fluorescent in nature. The polymer-bound thionine and phenosafranine dyes in aqueous solution exhibit biexponential fluorescence decay, in contrast with the corresponding unbound dye, which is attributed to the effect of the macromolecular chain conformation and solvent environment on the photophysics of the polymer-bound dyes. The excited state which decays with a shorter lifetime is suggested to be in a more polar aqueous environment (as in the case of the unbound dyes dissolved in aqueous medium), whereas the excited state which shows a longer lifetime is situated in a hydrophobic environment inside the coil of the polymeric chain where less interaction with the solvent molecules is experienced.