Theoretical investigation of molecular excited states of polar organic monolayers via an efficient embedding approach

In this work, we present a theoretical investigation on excitation energies of organic molecules embedded in a periodic monolayer. We use the self-consistent periodic-image-charges embedding approach, which takes into account all the electrostatic effects, to compute the perturbation on molecular orbitals and eigenvalues due to the presence of the surrounding periodic array of polar molecules. We considered vanadyl naphthalocyanine, mercaptobiphenyl, and tris-(8-hydroxyquinoline) aluminum (AlQ3) at different coverages, and excitation energies computed using the time-dependent density-functional theory. We found a significant (0.1-0.2 eV) red- or blue-shift of the energies for different excited states, due to the different coupling of the molecule with the polarization field of the two-dimensional crystal.