The structural organization of conjugated polymers at buried interfaces plays a decisive role in determining their optical and electronic properties. However, experimental tools to probe such interfacial features remain limited. In this work, ultraviolet–visible attenuated total reflectance (UV–vis ATR) spectroscopy was applied to thin films of poly(3-hexylthiophene-2,5-diyl) to enable selective characterization of the polymer–substrate interface. ATR spectra revealed a distinct absorption peak near 690 nm, which was absent in corresponding transmission spectra. Time-dependent density functional theory (TD-DFT) calculations demonstrated that this band originates from polymer chains with a planar backbone with a small C–C–C–S dihedral angle, which is distinct from conventional aggregate structures. Thermal treatment and solvent-dependent film preparation further confirmed the interfacial origin and structural sensitivity of the 690 nm feature. These findings establish UV–vis ATR spectroscopy as a powerful approach to uncover interface-specific molecular arrangements in conjugated polymer films and provide new insights into structure–property relationships that are critical for organic electronic devices.
Tanaka et al. (Mon,) studied this question.