Inverse isotope effects in the superconductivity of acenes: a theoretical study

Electron–phonon coupling constants are calculated for organic molecular crystals of anthracene, tetracene, and pentacene and their full deuterides. We find that the low-frequency C–C–C in-plane modes of 200–400 cm−1 and the C–C stretching modes of 1400–1600 cm−1 play an important role in the electron–phonon coupling in these acenes. Inverse isotope effects for hydrogen–deuterium substitution are predicted in the superconductivity of acenes. Such inverse isotope effects can be explained by electron–phonon couplings in the C–C stretching modes, which significantly increase by deuterium substitution.