Polyaniline Doping by α,α-Difluoro-β-amino Acids

Currently, polyaniline (PANI) is considered as a promising polymer that can be used in biosensors, drug delivery systems, bioelectronics, etc. Its biocompatibility can be strongly improved by using dopants with biofunctionality. This study reveals the protonation/doping of PANI by fluorinated analogs of natural amino acids, namely, α,α-difluoro-β-amino acids (DFAAs) with alkyl and aromatic tails in N-methylpyrrolidone solutions. We find that these acids can dope PANI due to both the weakened basicity of their amino groups because of two fluorine atoms in α,α-positions and specific intermolecular interactions (π-π stacking, alkyl-π, F-π) of their tails with units of PANI chains. These interactions did not give the doped PANI salts with high conductivity but led to formation of stable PANI-DFAA complexes, which were confirmed both by clear changes in the UV-Vis and Fourier transform infrared spectra of the protonated/doped PANI and by their conductivity of ∼10^-6 S/cm. Our results suggest an applicability of such PANI complexes as carriers of DFAA for their biomedical applications.