The quantum‐chemical study of small clusters of organic chromophores: Topological analysis and nonlinear optical properties

Structure and nonlinear optical properties of small clusters formed of organic chromophores through H‐bonding are studied by the example of dimer and trimer of p ‐nitroaniline (PNA). The analysis of the electron charge density pattern in the bonding region in terms of “Atoms in Molecules” approach is performed, and the values of electron charge density, Laplacian of electron density at critical points, etc. are determined. Topological analysis has given evidence of the existence of three‐center interaction of one amino group hydrogen with oxygens of nitro group of the neighboring PNA, resulting in two H‐bond formation. Solvent effect on the static (hyper)polarizability of the clusters is studied by the example of PNA dimer in acetone in the framework of conventional Polarizable Continuum Model as well as supermolecule and semicontinuum approaches. The essential increase of the cluster hyperpolarizability in comparison with that of a single chromophore is obtained. The account of specific interaction with the solvent molecule is shown to result in moderate or significant enhancement of β ∥ depending on the structure of the formed cluster. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008