Vibronic interactions and superconductivity in acenes

Electron–phonon coupling constants are calculated in organic molecular crystals such as benzene, naphthalene, anthracene, tetracene, pentacene, and hexacene. We find that the C–C stretching modes of 1400–1600 cm−1 extensively play an important role in the electron–phonon coupling in the smaller molecules such as benzene, naphthalene, and anthracene, while the lowest frequency mode becomes relatively important for electron–phonon coupling in the larger molecules such as tetracene, pentacene, and hexacene. Finally, we derive experimental superconductive transition temperatures Tcs of anthracene, tetracene, and pentacene, and estimate the possible Tcs of benzene, naphthalene, and hexacene. According to our calculation, benzene, naphthalene, and hexacene are expected to have the Tcs at 25.3, 7.4, and 1.3 K, respectively, and thus Tcs would become much smaller and smaller as the molecular sizes become larger from benzene to hexacene.