Molecular dynamics of a polyaniline/β-cyclodextrin complex investigated by 13C solid-state NMR.

The molecular dynamics of a polyaniline/β-cyclodextrin inclusion complex (PANI/β-CD IC) and its relation with optical properties were investigated using high-resolution solid-state (13)C nuclear magnetic resonance (NMR) and optical absorption spectroscopies. UV-vis measurements revealed a π-π* absorption peak of a PANI film that had a 10 nm blue-shift by inclusion of β-CD, indicating that π-conjugation of PANI was shortened in the IC. Temperature dependent analysis of (13)C NMR spectra and spin-lattice relaxation times (T(1C)) revealed that the inclusion induced acceleration of the twisting motion of the PANI chain. Moreover, two twisting motions attributed to different torsional angle modes were observed following Arrhenius plots of T(1C) measurements, and the twisting frequency and angle increased above -25 °C. These results suggest that the β-CD inclusion weakens the intermolecular π-π interaction and enhances the accompanying twisting motion, consequently leading to a blue-shift of UV-vis absorption.