Espectroscopia de absorção de dois fótons em moléculas orgânicas incluindo efeitos de solvente

Abstract

1. Bistafa, C.; Ramos, T. N.; Coutinho, K.; Canuto, S. Quantum mechanics meets scaling theory near the critical point (submetido). 2. Ramos, T. N.; Canuto, S.; Champagne, B. Unraveling the electric field induced second harmonic generation responses of stilbazolium ion pairs complexes in solution using a multiscale simulation method (submetido). 3. Ramos, T. N.; Silva, D. L.; Cabral, B. J. C.; Canuto, S. On the Spectral Line Width Broadening for Simulation of the Two-Photon Absorption Cross-Section of Para-Nitroaniline in Liquid Environment. . grandes que a utilização de métodos semi-empíricos, os quais apresentam baixo custo computacional, pode fornecer descrições mais precisas para as intensidades de A2F, em particular quando excitações duplas são incluídas. Por fim, utilizando simulações moleculares de complexos neutros constituídos por pares iônicos mostramos que a resposta Electric Field-Induced Second Harmonic Generation é modulada pela posição relativa do ânion. Esta dependência ocorre principalmente devido às variações do momento de dipolo e não devido às variações das componentes da primeira hiperpolarizabilidade. Palavras-chave: Absorção de dois fótons, EFISHG, solvatação, S-QM/MM. ABSTRACT The electronic properties related with the two-photon absorption process (TPA) in isolated or solvated organic molecules were studied aiming at characterizing the electronic transitions, tune the TPA intensity and to suggest a way to assign the value of the spectral broadening parameter, including solvent effects. The solvent effects were included using explicit solvation with Born-Oppenheimer Molecular Dynamics, Classical Molecular Dynamics and Monte Carlo Metropolis sampling as well the implicit solvation with Polarizable Continuum Model. Employing the Sequential-Quantum Mechanics / Molecular Mechanics we evaluate different procedures to convolute the TPA spectrum and to obtain the respective TPA cross-section. Considering the contributions of sampled configurations from molecular simulations we suggest a fit of the full width at half maximum of the TPA band. This fit resulted in better description of the maximum value and the relative intensity of the TPA cross-sectionof the para-Nitroaniline in liquid environments. A strategy using external electrostatic fields enhanced the TPA cross-section was also explored for two betaines. The presence of the field reduced the transition probability of the one-photon absorption (OPA), highlighting the potential use to avoid spurious effects from OPA in the TPA process applications. We showed for large molecular systems that using semi empirical methods, which are computationally cheap, can provide more accurate descriptions for the TPA intensities, especially when the double excitations are included in the calculations. Using molecular simulations of ion pairs as neutral complexes we showed that the Electric Field-Induced Second Harmonic Generation response is tuned by the anion relative position. This dependence become of the anion ability to change the dipole moment and it i...