Computer Simulation of the Nonlinear Optical Properties of Langmuir–Blodgett Films of a Squaraine Derivative

Abstract

The linear and nonlinear optical properties (L&NLO) of a monolayer of (4-(N-methyl-N-(carboxypropyl)amino)-phenyl-4′-(N,N-dibutylamino)phenylsquaraine (SBA) were computed by a combination of molecular dynamics simulations, molecular quantum-mechanical, and discrete local-field model calculations to compute the macroscopic optical susceptibilities. Langmuir films on water and graphite were simulated and several structural properties investigated. In addition, SBA in water and dimethylsulfoxide (DMSO) solutions were simulated, and the aggregation behavior of SBA in these solvents was analyzed. The molecular (hyper)polarizabilities of SBA were calculated with density functional theory and validated with MP2 correlated ab initio calculations. An unusual large component perpendicular to the molecular dipole moment is obtained for the molecular first hyperpolarizability, which is a main contributor to the large in-plane anisotropy of the computed macroscopic second-harmonic generation signal of the Langmuir–Blo...