  Graphene electrodes are promising candidates to improve reproducibility and
stability in molecular electronics through new electrode-molecule anchoring
strategies. Here we report sequential electron transport in few-layer graphene
transistors containing individual curcuminoid-based molecules anchored to the
electrodes via pi-pi orbital bonding. We show the coexistence of inelastic
co-tunneling excitations with single-electron transport physics owing to an
intermediate molecule-electrode coupling; we argue that an intermediate
electron-phonon coupling is the origin of these vibrational-assisted
excitations. These experimental observations are complemented with density
functional theory calculations to model electron transport and the interaction
between electrons and vibrational modes of the curcuminoid molecule. We find
that the calculated vibrational modes of the molecule are in agreement with the
experimentally observed excitations.
