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

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 red-shifted 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.