Theoretical study in gas phase of linear and nonlinear optical properties of the ortho-, meta- and para-nitrophenol isomers

The Role of Aqueous Solvation on the Intersystem Crossing of Nitrophenols

The photochemistry of nitrophenols is a source of smog as nitrous acid is formed from their photolysis. Nevertheless, computational studies of the photochemistry of these widespread toxic molecules are scarce. In this work, the initial photodeactivation of ortho-nitrophenol and para-nitrophenol is modeled, both in gas phase and in aqueous solution to simulate atmospheric and aerosol environments. A large number of excited states, six for ortho-nitrophenol and 11 for para-nitrophenol, have been included and were all populated during the decay. Moreover, periodic time-dependent density functional theory (TDDFT) is used for both the explicitly included solvent and the solute. A comparison to periodic QM/MM (TDDFT/MM), with electrostatic embedding, is made, showing notable differences between the decays of solvated nitrophenols simulated with QM/MM and full (TD)DFT. A reduced intersystem crossing in aqueous solution could be observed thanks to the surface hopping approach using explicit, periodic TDDFT solvation including spin-orbit couplings.

Microscopic Origin of Different Hydration Patterns of para-Nitrophenol and Its Anion: A Study Combining Multiconfigurational Calculations and the Free-Energy Gradient Method

A theoretical study of the solvatochromic shifts of para-nitrophenol ( pNP) and para-nitrophenolate anion ( pNP^-) in aqueous solution is presented using a QM/MM methodology with molecular dynamics simulation. The optimized structures in aqueous solution are obtained using both the polarizable continuum and the free-energy gradient methods. For pNP, the calculated redshifts at the CASPT2 (12,10) level are, respectively, 0.71 and 0.94 eV, in good agreement with the experimental ones (0.80-0.83 eV), whereas for pNP^-, they are small. The difference between the solvatochromic shifts of pNP and pNP^- is calculated as 0.71 eV in good agreement with the experimental one (0.79-0.81 eV). Finally, these shifts are understood in terms of the solvent effect on the solute structure, accurately calculated by the present theoretical treatment.

Solvation effects on the static and dynamic first-order electronic and vibrational hyperpolarizabilities of uracil: a polarized continuum model investigation

Electronic (β(e)) and vibrational (β(v)) first-order hyperpolarizabilities of uracil were determined in gas and water solution using the Coulomb-attenuating Density Functional Theory level with the Dunning's correlation-consistent aug-cc-pVDZ basis set. Frequency-dependent β(e) values were computed for the Second Harmonic Generation (SHG) and Electric Optical Pockels Effect (EOPE) nonlinear optical phenomena. The Polarized Continuum Model was employed to study the solvent effects on the electronic and vibrational properties. The introduction of solvation contributions increases the β(e) (static) value by ca. 110%. In comparison, smaller enhancements are found for the β(e) (EOPE) and β(e) (SHG) data evaluated at the typical wavelength of 694 nm (by 40-50%). The gas-water hyperpolarizability difference was rationalised through a density analysis study. The magnitudes of the vibrational first-order hyperpolarizabilities are comparable to their electronic counterparts and noticeably increase in solution: β(v) (EOPE) ~ β(e) (EOPE) in aqueous phase at λ = 694 nm. Analysis of the IR and Raman spectra is useful to elucidate the most important contributing modes to the vibrational first-order hyperpolarizabilities.