Abstract
The effects of deuterium isotope substitution on conjugated polymer chain stacking of poly(3-hexylthiophene) is studied experimentally by X-ray diffraction (XRD)
in combination with gel permeation chromatography and theoretically using density functional theory and quantum molecular dynamics. For four P3HT materials with
different levels of deuteration (pristine, main-chain deuterated, side-chain deuterated, and fully deuterated), the XRD measurements show that main-chain thiophene deuteration
significantly reduces crystallinity, regardless of the side-chain deuteration. The reduction of crystallinity due to the main-chain deuteration is a quantum nuclear effect resulting from a static zero-point vibrational energy combined with a dynamic correlation of the dipole fluctuations. The quantum molecular dynamics simulations confirm the inter-chain correlation of the proton-proton and deuteron-deuteron motions, but not of the proton-deuteron motion. Thus, isotopic purity is an important factor affecting stability and properties of conjugated polymer crystals, which should be considered in the design of electronic and spintronic devices.
