Spectral Shift of the n → π* Transition for Acetone and Formic Acid with an Explicit Solvent Model

Abstract

In our recent work, a new form of the electrostatic solvation energy for the nonequilibrium polarization has been derived by introducing the method of constrained equilibrium state in the framework of continuous medium theory. Up until now, the idea of the constrained equilibrium state method has not been introduced into the explicit solvent model by others; therefore this nonequilibrium energy form was further equivalently extended to the explicit solvent model in this work based on the discrete representation of the solvent permanent charges and induced dipoles. Making use of this expression in explicit solvent model, we modified the nonequilibrium module in the averaged solvent electrostatic potential/molecular dynamics program to implement numerical calculations. Subsequently, the new codes were applied to study the solvatochromic shifts of the n → π* absorption spectra for acetone and trans-formic acid in aqueous solution. The calculation results show a good agreement with the experimental observations. When our results of spectral shift are compared with those achieved directly from the continuum model, it can be seen that both the explicit solvent model and continuum model derived based on the constrained equilibrium approach can give reasonable predictions. The hydrogen bond effect was also discussed and deemed to be a dominant contribution to the spectral shift by calculating the n → π* absorption spectra of acetone-water complexes.

Oenin and Quercetin Copigmentation: Highlights From Density Functional Theory

“…It is noteworthy that this study is based on the implicit solvent model (Li et al, 2011a , b ). An explicit description of the solvent (Trouillas et al, 2015 , 2016 ) could modify the obtained results in that it may change the hydrogen pattern and the relative stability of the conformers.…”

“…Vibrational frequency calculations were performed with the same method to verify that each obtained structure is a minimum on the potential surface, and to get corrections for thermodynamic functions. Integral equation formalism polarizable continuum model (IEFPCM) was used to describe water solvent effect in all calculations except spectral evaluation (Li et al, 2011a , b ; Trouillas et al, 2015 , 2016 ).…”

“…Different from experiments, a quantum mechanical (QM) screening allows to get structures and properties of copigmentation systems (Quartarolo and Russo, 2011 ; Di Meo et al, 2012 ; Kalisz et al, 2013 ; Rustioni et al, 2013 ; Trouillas et al, 2015 , 2016 ), such as binding energies and spectral shifts, in a quicker, time-saving and money-saving way. This implies the use of a reliable theoretical model which consists in a good strategy for searching the most stable conformers of copigmentation complex in the conformational space, in an appropriate choice of the QM methods for geometry optimization, energetic and spectral calculations and in a reliable description of solvation effects (Li et al, 2011a , b ; Nave et al, 2012 ; Rustioni et al, 2013 ; Trouillas et al, 2015 , 2016 ; Marpaung et al, 2017 ). Actually, finding out the most stable conformer can be done by calculations totally based on a QM approach, starting from few most probable orientations, or by a preliminary molecular dynamics (MD) simulation followed by a QM refinement (Di Meo et al, 2012 ; Trouillas et al, 2015 , 2016 ).…”

Solvent effect on electronic absorption, fluorescence, and phosphorescence of acetone in water: Revisited by quantum mechanics/molecular mechanics (QM/MM) simulations

“…[1][2][3][4][5][6][7][8][9][10] Although many computational works [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] have been devoted to the study of electronic absorption in aqueous acetone, its fluorescence spectra received limited theoretical attentions [26][27][28][29][30] due to the difficulty of simulating excited state dynamics. Moreover, the magnitude of the solvent effect on the n ← π * (S 1 → S 0 ) emission is still controversial to some extent despite of the fact that it has been well recognized that the water effect on the n → π * (S 0 → S 1 ) absorption is a blueshit of ∼0.2-0.3 eV.…”

Modeling Solvent Effects on Electronic Excited States

“…There have been other applications of the QM/MM methodology that include solvent polarization response, including recent work by Li and co-workers. 64 Interested readers are referred to a very recent comprehensive review of such methods. ' REFERENCES An important reason for the success of the QMÀEFP approach is that the EFP method includes self-consistent polarizability that allows the solvent to respond to the changing electron density of the solute upon excitation.…”