A new method to characterize local conformations of aromatic imide compounds and polyimides was established via Fourier transform infrared (IR) spectroscopy at low frequencies (far-IR) and density functional theory (DFT) calculations. The far-IR spectrum of an imide model compound (sBPDA/An) was well reproduced by the DFT calculations in the 650-100 cm(-1) range by considering local molecular conformations and the effects of neighboring molecules. The conformations of 3,30,4,4'-biphenyl-tetracarboxylic (sBPDA) type polyimide films were subsequently analyzed using their far-IR spectra compared with the calculated spectra of sBPDA/An. The dihedral angle between biphenyldiimide moieties (phi) tends to be coplanar in the highly ordered region, whereas that between phthalimide and phenylene (omega) tends to be more twisted. Conformation dependent far-IR is a facile and versatile tool to estimate local conformations of aromatic polymers. (C) 2016 Elsevier Ltd. All rights reserved.