Emission of thioflavin T and its off-on control in polymer membranes

Abstract

The absorption and emission spectral properties of thioflavin T (TFT⁺) in Nafion (Nf) and cellulose matrices have been studied. Formation of the emittive dimer is observed in both matrices. The monomer TFT⁺ emission is blueshifted in Nafion membrane (Nf), whereas it is redshifted in cellulose membrane when compared with the emission in aqueous solution. The dimer emission of TFT⁺ in the Na⁺-Nf membrane undergoes off-on switching with acids and alkalis. The TFT⁺ molecule undergoes protonation in the H⁺-Nf and the protonated dye is fluorescent. The dimer emission of TFT⁺ is not observed in the dry H⁺-Nf membrane because of the protonation of the TFT+ molecule. The diffusion coefficient and the free energy of hydrophobic interaction for the TFT⁺ molecule in the Nf membrane are calculated. The TFT⁺ molecule experiences hydrophobic and electrostatic interactions in the Nf matrix, whereas it experiences a polar environment in the cellulose membrane. The 3D emission spectral studies support the formation of the emittive dimer in both Nf and cellulose matrices.