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

Abstract

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 (AlQ 3 ) 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 blueshift of the energies for different excited states, due to the different coupling of the molecule with the polarization field of the two-dimensional crystal.

CLUSTERGEN: a program for molecular cluster generation from crystallographic data

“…Such an approach can be realized using various quantum mechanics/molecular mechanics (QM/MM) schemes (Bjornsson & Bü hl, 2012). It has been recently shown that constrained QM/MM geometry optimizations of excited state species provide almost quantitative agreement with the experimental results (Benedict et al, 2011;Makal et al, 2012Makal et al, , 2011Terentjevs et al, 2012). Moreover, this method is computationally cheap and robust.…”