Short- and Long-Range Solvation Effects on the Transient UV–Vis Absorption Spectra of a Ru(II)–Polypyridine Complex Disentangled by Nonequilibrium Molecular Dynamics

Abstract

Evidences of subtle effects in the dynamic reorganization of a protic solvent in its firstand farther-neighbor shells, in response to the sudden change in the solute's electronic distribution upon excitation, are unveiled by a multi-level computational approach. By combining non-equilibrium molecular dynamics and quantum mechanical calculations, the experimental time evolution of the transient T 1 absorption spectra of an heteroleptic Ru(II)polypyridine complex in ethanol or di-methyl sulfoxide solution is reproduced and rationalized in terms of both fast and slow solvent re-equilibration processes, which are found responsible for the red shift and broadening experimentally observed only in the protic medium. Solvent orientational correlation functions and a time-dependent analysis of the solvation structure confirm that the initial, fast observed red shift can be traced back to the destruction/formation of hydrogen bond networks in the first-neighbor shell, whereas the subsequent shift, evident in the [20-500] ps range and accompanied by a large broadening of the signal, is connected to a collective re-orientation of the second and farther solvation shells, which significantly changes the electrostatic embedding felt by the excited solute.

Critical Role of Protons for Emission Quenching of Indoline Dyes in Solution and on Semiconductor Surfaces

“…Due to the charge transfer nature of the lowest-energy excited state in D149, moving the electronic density from the indoline donor (the N electron-rich atom) to the rhodanine anchoring group, we can expect a consequent change in the topology and strength of CAA− D149 H-bond interactions going from S0 to S1, similarly to what was found by some of us for Z907 in protic solvents. 52,53 Thus, we examined various D149−CAA complexes by fully optimizing the structure in both ground and lowest-energy excited states, and considering all of the possible electron-rich atoms in the molecule and two different D149 isomers, termed D149a and D149b, differing for the rotation of the COOH anchoring group, as shown in Figure S5. While D149a is slightly more stable in S0 (by about 2 kJ/mol), D149b, where the H-bond is established between the COOH unit and a carbonyl oxygen of the rhodanine, becomes the lower-energy structure in S1 (about 6 kJ/mol), as shown by the relative energies in Table S2.…”

Iron’s Wake: The Performance of Quantum Mechanical-Derived Versus General-Purpose Force Fields Tested on a Luminescent Iron Complex

“…To conclude, we emphasize the level of accuracy achieved by J oyce FF in describing the geometries of TMCs in realistic conditions with a computational cost which is orders of magnitude lower with respect to the QM method of reference. This methodology, combined to a suitable QM method for the calculation of the excited properties of TMCs, opens the door to perform further analysis which can be used to provide a deed understanding of the photo-physical phenomena measured experimentally (i.e., transient UV−Vis absorption spectra [ 59 ]), which are beyond the scope of this work.…”

“…Hybrid molecular mechanics (MM) and quantum mechanics (QM) schemes (QM/MM) can be useful to overcome limitations due to the size of the system, as the solute can be treated at QM level and the solvent molecules by means of classical force fields (FF) [ 55 , 56 ], however, still sub nanosecond timescale can only be simulated. Thus, classical techniques such as molecular dynamics (MD) [ 57 , 58 ], allowing for much longer simulations (>ns), remain the only viable approach to generate a meaningful statistical analysis of the solvent structure as well as of its response to the changes in the solute electronic distribution [ 59 ]. The reliability of classical MD simulations, however, in turn depends on the accuracy of the employed FF, that is on the potential energy functions used to approximate the system’s total energy as the nuclei move [ 57 , 60 , 61 , 62 , 63 ].…”

Ultrafast Spectroscopy of Fe(II) Complexes Designed for Solar‐Energy Conversion: Current Status and Open Questions

“…As far as CT transitions are concerned, surrounding solvent molecules, feeling the change in the chromophore electron density are expected to reorganize, potentially influencing both the energetics and dynamics of the excited state. [70][71][72][73][74] To accurately account for solvent reorganization effects, ideally an explicit description of the medium is required, resorting to ab initio or classical molecular dynamic (MD) simulations [75] or hybrid quantum mechanics/molecular mechanics (QM/MM) schemes. While for surface hopping simulations, the solvent can be readily incorporated by using QM/MM approaches, [76] for non-adiabatic and quantum dynamics calculations this is not straightforward and, usually, the diabatic PES of large coordination compounds are calculated in vacuum, with, however, some recent exceptions resorting to non-equilibrium implicit solvation terms in the model Hamiltonian.…”