Abstract
As seen in experiments with poly(3‐hexylthiophene), substitution of hydrogen with deuterium on the main chain alone decreases crystallinity. To understand this effect, a general formalism for analysis of the dipole moments and polarizabilities incorporating quantum nuclei, is developed. The formalism, based on quantum dynamics of the proton/deuteron and on the perturbative analysis of the dipole interaction energy, accounts for the anharmonicity of a potential energy surface and for the anisotropy of molecular dipole moments. The formalism is implemented within the Discrete Variable Representation and the Density Functional Theory describing, respectively, the quantum proton/deuteron on the thiophene ring and the electronic structure of the 27‐atom model polymer chain, embedded into a larger crystalline environment. The isotope effect is mainly attributed to the differences in the zero‐point energy of the CH/CD bonds and to the isotope‐dependence of the dipole‐dipole inter‐chain interactions.
