Commutation of second-order nonlinear optical responses of indolino-oxazolidines : from molecules in solution to functionalized surfaces

This thesis reports on a detailed characterization of the second harmonic generation (SHG) responses of indolino-oxazolidine derivatives in different environments. These molecular switches are particularly interesting because they can commute between a colorless closed form and a colored open form when triggered by various external stimuli. The two forms display different second-order nonlinear optical (NLO) responses and a huge contrast of the associated value, making these systems interesting for applications in molecular-scale memory devices with multiple storage and nondestructive read-out capacity. In particular, this thesis demonstrates that the performance of the NLO switches remains when forming self-assembled monolayers (SAMs). This investigation is carried out by using a multi-disciplinary approach that combines measurements of the linear and nonlinear optical responses of the switches in solution with theoretical chemistry calculations performed for molecules in solutions as well as in SAMs. The main results include 1 ) a comparative analysis of the hyper-Rayleigh scattering (HRS) and electric-field induced SHG (EFISHG) responses of the molecules in solution, demonstrating they could be much different owing to the amplitude and orientation of the dipole moment as well as to the non-negligible third-order NLO contribution to EFISHG, 2 ) the investigation of the effects of adding an acceptor nitro group on the oxazolidine of substituting the bithiophene donor group by an alternative ferrocene unit, which both reduce the contrast, and 3 ) the implementation and optimization of a multi-scale numerical method (MD-then-QM) to predict the NLO responses of dynamical systems, which consists in sampling the system geometries and structures using molecular dynamics (MD) and then in evaluating the NLO responses at ab initio quantum mechanical levels (QM). These results as well as the implemented method open the way to investigate new dynamical systems and to design efficient NLO switches.