Heibbe's Group

Research Group under Prof. Dr. Heibbe Cristhian B. de Oliveira

Thiago Lopes

New Paper at The Journal of Physical Chemistry B

Explicit Aqueous Solvation Treatment of Epinephrine from Car–Parrinello Molecular Dynamics: Effect of Hydrogen Bonding on the Electronic Absorption Spectrum

Arsênio P. Vasconcelos, Daniel F. S. Machado, Thiago O. Lopes, Ademir J. Camargo and Heibbe C. B. de Oliveira

The electronic absorption spectrum of the neurotransmitter epinephrine (EPN) in water solution is studied, combining ab initio Car–Parrinello molecular dynamics (CPMD) with a quantum mechanical approach within the framework of the time-dependent density functional theory (TDDFT) scheme. By selecting 52 uncorrelated snapshots, the excitation modes were calculated at the LC-ωPBE/6-31+G(d) level of theory, using an optimal range-separation parameter ω, determined by means of the gap-tuning scheme in the presence of the solvent molecules. By comparing with static approaches (vacuum and implicit solvation), we show here that explicit solvation treatment dramatically enhances the photophysical properties of the EPN, especially because of the more realistic dynamic description of the molecular geometry. The agreement between the simulated and experimental spectra is demonstrated when TDDFT calculations are performed with the optimally tuned version of the DFT hybrid, not only improving the relative intensities of the absorption bands but also the λmax position. These results highlight that accounting for the nuclear motions, that is, thermal effects (of both chromophore and solvent molecules), is imperative to predict experimental absorption spectra. In this paper, we have addressed the critical importance of explicit solvation effects on the photophysics of the EPN, raking in performance when the simulation is performed based on first-principles molecular dynamics such as CPMD.

Thesis Defense of Thiago Lopes

Title: "Bond Ellipticity Alternation: An Accurate Descriptor of the Nonlinear Optical Properties of π-Conjugated Chromophores"
Adivisor: Heibbe Cristhian Benedito de Oliveira
Committee members: Elaine Rose Maia, Ricardo Gargano and Clodoaldo Valverde



New Paper at Journal of Physical-Chemical Letters

TOC Graph Image
Bond Ellipticity Alternation: An Accurate Descriptor of the Nonlinear Optical Properties of pi-Conjugated Chromophores

Thiago O. Lopes, Daniel F. Scalabrini Machado, Chad Risko, Jean-Luc Brédas, and Heibbe C. B. de Oliveira

Well-defined structure–property relationships offer a conceptual basis to afford a priori design principles to develop novel π-conjugated molecular and polymer materials for nonlinear optical (NLO) applications. Here, we introduce the bond ellipticity alternation (BEA) as a robust parameter to assess the NLO characteristics of organic chromophores and illustrate its effectiveness in the case of streptocyanines. BEA is based on the symmetry of the electron density, a physical observable that can be determined from experimental X-ray electron densities or from quantum-chemical calculations. Through comparisons to the well-established bond-length alternation and π-bond order alternation parameters, we demonstrate the generality of BEA to foreshadow NLO characteristics and underline that, in the case of large electric fields, BEA is a more reliable descriptor. Hence, this study introduces BEA as a prominent descriptor of organic chromophores of interest for NLO applications.

New Paper at The Journal of Physical Chemistry C

TOC Graph paper JPCC 2017
Strong Solvent Effects on the Nonlinear Optical Properties of Z and E Isomers from Azo-Enaminone Derivatives

Daniel F. S. Machado, Thiago O. Lopes, Igo T. Lima, Demétrio A. da Silva Filho, and Heibbe C. B. de Oliveire

We calculated the nonlinear optical properties of 24 azo-enaminone derivatives, incorporating solvent effects on their geometric and electronic structure, to assess the impact of the environment on these properties. Namely, we incorporated chloroform, tetrahydrofuran, acetone, ethanol, methanol, and dimethyl sulfoxide in our calculations and compared our results incorporating solvent effects with our gas-phase calculations. To account for the electron correlation effects on NLO properties, we performed the calculations at MP2/6-31G(p)//MP2/6-31G(d) level set. The polarizable continuum model was used to simulate the presence of the solvent. The exponents of p extra functions added to heavy atoms were obtained, imposing the maximization of the first hyperpolarizability. Two structural configurations (Z and E) of azo-enaminones were investigated to assess the isomeric effects of the electric properties. Our results show that both solvent polarity and relative strength of the donor groups have a significant impact on the electric properties but more strikingly on the first hyperpolarizability β.