Reduction of Emeraldine Base Form of Polyaniline by Pillar[5]arene Based on Formation of Poly(pseudorotaxane) Structure

We report on the reduction of polyaniline (PANI) by pillar[5]arene based on the formation of the poly(pseudorotaxane) structure. When pillar[5]arene was mixed with emeraldine base (EB) form of PANI, a blue solution color resulting from the EB form of PANI was diluted over time, and became completely colorless after 180 min. The FT-IR spectrum of the mixture of the EB form of PANI and pillar[5]arene displayed a new band at 1646 cm–1, which was assigned the CO stretching band of benzoquinone. These results indicate that both oxidation of the hydroquinone units of pillar[5]arene and reduction of the EB form of PANI were induced by mixing the EB form of PANI and pillar[5]arene. Pillar[5]arene showed a stronger reducing ability than the unit model of hydroquinone. The ROE correlations between the methylene bridge protons of pillar[5]arene and the benzene protons of PANI indicated that the PANI chain was included into the pillar[5]arene cavity. Formation of the poly(pseudorotaxane) structure between PANI and pillar[5]arene was the main reason for the strong reducing ability of the EB form of PANI.