QM/MM investigation of the electric field-induced second harmonic generation (EFISHG) response of ion pairs in solution

• Grant number: 18/17453-1
• Support Opportunities: Scholarships abroad - Research Internship - Doctorate
• Start date: November 01, 2018
• End date: April 30, 2019
• Field of knowledge: Physical Sciences and Mathematics - Physics - Atomic and Molecular Physics
• Principal Investigator: Sylvio Roberto Accioly Canuto
• Grantee: Tárcius Nascimento Ramos
• Supervisor: Benoit Champagne
• Host Institution: Instituto de Física (IF). Universidade de São Paulo (USP). São Paulo , SP, Brazil
• Institution abroad: University of Namur (UNamur), Belgium
• Associated to the scholarship: 15/14189-3 - Two-Photon Absorption Spectroscopy in Organic Molecules Including Solvent Effects, BP.DR

Abstract

The project aims at simulating the electric field-induced second harmonic generation (EFISHG) responses of ions pairs in low dielectric constant solvents. The EFISHG technique is a wellknown technique to determine the first (b) and the second (g) hyperpolarizabilities of compounds in solutions. However, owing to the application of an external static electric field necessary to break the centro-symmetry, this technique cannot be applied to charged compounds. Still, it can be applied to ions pairs as shown by recent works due to Cariati and co-workers. To our knowledge, the EFISHG hyperpolarizabilities of ions pairs have little been investigated using theoretical chemistry methods whereas a few experimental works have been reported, including on stilbazolium derivatives as well as on pH-triggered molecular switches.The nature of these systems calls for a sequential approach, combining 1°) Molecular Mechanics (MM) simulations using appropriate force fields with 2°) ab initio calculations of the NLO properties by accounting for explicit solvent molecules. Following the works of the group in Sao Paulo spatial distributions of ions pairs and solvent molecules will first be generated using Monte Carlo simulations where the intermolecular interactions are described using the Lennard-Jones potentials and Coulomb terms. Then, a reduced number of statistically-uncorrelated configurations will be sampled and submitted to ab initio (time-dependent Hartree-Fock and time-dependent density functional theory) calculations of the first and second hyperpolarizabilities. This project will extent previous works carried out by the groups in Namur and Sao Paulo on calculating the second-order NLO properties of molecules in solution, with explicit consideration of the solvent molecules. The sequential MM-then-QM method will be applied to stilbazolium (a cation) derivatives for which there exist experimental EFISHG data obtained for different counteranions. The NLO results will be analyzed at the light of the structures of the ions pairs and their solvent shells as well as by making relationships with the linear optical properties (UV/visible absorption spectra). Besides the ions pairs structures, it will be interesting 1°) to investigate the impact of the geometrical fluctuations on the NLO responses and 2°) to compare the amplitudes of the second- and third-order NLO responses. Possible extension of this work will be the prediction and interpretation of the two-photon absorption spectra (which is another third-order NLO process) as well as of hyper-Rayleigh scattering responses (corresponding to another second-order response, which can be determined experimentally for both neutral and charged species).

Scientific publications

(References retrieved automatically from Web of Science and SciELO through information on FAPESP grants and their corresponding numbers as mentioned in the publications by the authors)

RAMOS, TARCIUS N.; CANUTO, SYLVIO; CHAMPAGNE, BENOIT. Unraveling the Electric Field-Induced Second Harmonic Generation Responses of Stilbazolium Ion Pairs Complexes in Solution Using a Multiscale Simulation Method. JOURNAL OF CHEMICAL INFORMATION AND MODELING, v. 60, n. 10, p. 4817-4826, OCT 26 2020. (15/14189-3, 18/17453-1)