The Influence of Electronic Polarization on Nonlinear Optical Spectroscopy

Abstract

The environment surrounding a chromophore can dramatically affect the energy absorption and relaxation process, as manifested in optical spectra. Simulations of nonlinear optical spectroscopy, such as two-dimensional electronic spectroscopy (2DES) and transient absorption (TA), will be influenced by the computational model of the environment. We here compare a fixed point charge molecular mechanics model and a quantum mechanical (QM) model of the environment in computed 2DES and TA spectra of Nile red in water and the chromophore of photoactive yellow protein (PYP) in water and protein environments. In addition to simulating these nonlinear optical spectra, we directly juxtapose the computed excitation energy correlation function to the dynamic Stokes shift function often used to analyze environment dynamics. Overall, we find that for the three systems studied here the mutual electronic polarization provided by the QM environment manifests in broader 2DES signals, as well as a larger reorganization energy and a larger static Stokes shift due to stronger coupling between the chromophore and the environment.

Ultrafast All-Optical Switching Using Doped Chromoprotein Films

“…The photocycles of BR and PYP in solution are depicted in Scheme , both showing fast, sub-picosecond to picosecond initial transitions. While the ultrafast kinetics of BR is well studied, − the ultrafast absorption kinetics of PYP in solution and crystalline form were only recently investigated. ,, At the same time, the role of environmental variables and structural details of newly engineered chromophore analogues on the ultrafast photocycle of PYP is still a subject of intensive research. − The existence of sub-picosecond initial transitions in dried, doped PYP films also needs confirmation.…”

Comparison of Linear Response Theory, Projected Initial Maximum Overlap Method, and Molecular Dynamics-Based Vibronic Spectra: The Case of Methylene Blue

“…Truncation at second order is exact for a system with a Gaussian distribution of energy gap fluctuations, which occurs for displaced harmonic potentials of the same frequency. Changing the frequency or rotating the potentials may introduce nonlinear coupling that can be partially captured by the third-order term, which is also able to incorporate some effects of anharmonic potentials. , In addition to being able to sample anharmonic nuclear configurations, a dynamic MD energy gap time-correlation function-based approach also describes coupling to an explicit solvent environment. ,,− …”

Elucidating the Role of Hydrogen Bonding in the Optical Spectroscopy of the Solvated Green Fluorescent Protein Chromophore: Using Machine Learning to Establish the Importance of High-Level Electronic Structure

“…Owing to these important uses, a wealth of previous studies have focused on characterizing how different chromophores’ excitations are tuned by the interactions with their chemical environment − in order to uncover the physical basis underlying these phenomena and guide the design of chromophores with particular target properties. Simulations of chromophores in protein scaffolds or in solution have also provided extensive insights into the coupling between the chemical environment and how the interplay of the electronic and nuclear dynamics gives rise to their linear and multidimensional optical spectra. − However, for chromophores in solvated condensed-phase environments, performing the required excited-state electronic structure calculations with a quantum treatment of the environment is extremely computationally costly, owing to the large system sizes (typically 300–500 atoms) needed to treat the chromophore and its environment. For condensed-phase systems, this electronic structure computational cost is combined with the need to perform many thousands of electronic structure calculations to account for the many thermally relevant configurations of the chromophore and solvent.…”