Modeling and analyzing a photo-driven molecular motor system: Ratchet dynamics and non-linear optical spectra

Abstract

A light-driven molecular motor system is investigated using a multi-state Brownian ratchet model described by a single effective coordinate with multiple electronic states in a dissipative environment. The rotational motion of the motor system is investigated on the basis of wavepacket dynamics. A current determined from the interplay between a fast photochemical isomerization (photoisomerization) process triggered by pulses and a slow thermal isomerization (thermalization) process arising from an overdamped environment is numerically evaluated. For this purpose, we employ the multi-state low-temperature quantum Smoluchowski equations that allow us to simulate the fast quantum electronic dynamics in the overdamped environment, where conventional approaches, such as the Zusman equation approach, fail to apply due to the positivity problem. We analyze the motor efficiency by numerically integrating the equations of motion for a rotator system driven by repeatedly impulsive excitations. When the timescales of the pulse repetition, photoisomerization, and thermalization processes are separated, the average rotational speed of the motor is determined by the timescale of thermalization. In this regime, the average rotational current can be described by a simple equation derived from a rate equation for the thermalization process. When laser pulses are applied repeatedly and the timescales of the photoisomerization and pulse repetition are close, the details of the photoisomerization process become important to analyze the entire rotational process. We examine the possibility of observing the photoisomerization and the thermalization processes associated with stationary rotating dynamics of the motor system by spectroscopic means, e.g. pump-probe, transient absorption, and two-dimensional electronic spectroscopy techniques.

Photophysics of First-Generation Photomolecular Motors: Resolving Roles of Temperature, Friction, and Medium Polarity

“…18,19 In general, a disadvantage of the second-generation motors is that the position of the photostationary state is typically less favorable than for the first generation, and the yield of the photochemical isomerization is significantly lower. 20−22 It is expected, and has been shown theoretically, 23,24 that the overall rotation speed will be a product of the photochemical quantum yield and rate of thermal helix inversion (provided these two are well separated in their timescales). Consequently, an ideal motor would combine the high photochemical quantum yield of the first generation with the fast thermal helix inversion of the second generation.…”

Statistical distributions of the tuning and coupling collective modes at a conical intersection using the hierarchical equations of motion

“…On the other hand, semi-classical strategies may lead to a questionable description of the quantum noise or of tunneling effect. An alternative description is dissipative dynamics 40 , which treats only implicitly the environment at any temperature with statistical Schrödinger equations [41][42][43] , multi-state quantum Fokker-Planck equation (MSQFPE) [44][45][46][47] , or master equations in Liouville space. Observables related to the selected active subspace can thus be obtained exactly in the framework of the harmonic baths with linear couplings by non-perturbative methods such as the "hierarchical equations of motion" (HEOM) formalism 48,49 .…”

Modeling and simulating the excited-state dynamics of a system with condensed phases: A machine learning approach

“…As shown in the previous paper, 48 the machine learning approach can be applied not only for a system described by electronic states but also a system described by reaction coordinates, which is useful for investigating chemical reaction processes characterized by potential energy surfaces. By combining the previous and present approaches, we can further investigate a system described as not only electronic states but also molecular configuration space in a framework of the system-bath model, for example, photoisomerization, 60 molecular motor, 61 and nonadiabatic transition problems. 62 In this way, we may construct a system-bath model for entire photosynthesis reaction processes consisting of photoexcitation, 1,2 exciton transfer, [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] electron transfer, [21][22][23][24][25] and proton transfer processes, [63][64][65] including the conversion processes, such as exciton-coupled electron transfer 66 and electron coupled proton transfer processes.…”