Polaron properties in 2D organic molecular crystals: directional dependence of non-local electron–phonon coupling

In organic molecular crystals, the polaronic hopping model for the charge transport assumes that the carrier lies at one or a small number of molecules. Such a kind of localization suffers the influence of the non-local electron–phonon (e–ph) interactions associated with intermolecular lattice vibrations. Here, we developed a model Hamiltonian for numerically describing the role played by the intermolecular e–ph interactions on the stationary and dynamical properties of polarons in a two-dimensional array of molecules. We allow three types of electron hopping mechanisms and, consequently, for the nonlocal e–ph interactions: horizontal, vertical, and diagonal. Remarkably, our findings show that the stable polarons are not formed for isotropic arrangements of the intermolecular transfer integrals, regardless of the strengths of the e–ph interactions. Interestingly, the diagonal channel for the e–ph interactions changes the transport mechanism by sharing the polaronic charge between parallel molecular lines in a breather-like mode.