High Magnetic Field Detunes Vibronic Resonances in Photosynthetic Light Harvesting

Abstract

The origin and role of oscillatory features detected in recent femtosecond spectroscopy experiments of photosynthetic complexes remain elusive. A key hypothesis underneath of these observations relies on electronic-vibrational resonance, where vibrational levels of an acceptor chromophore match the donor-acceptor electronic gap, accelerating the downhill energy transfer. Here we identify and detune such vibronic resonances using a high magnetic field that exclusively shifts molecular exciton states. We implemented ultrafast pump-probe spectroscopy into a specialized 25 T magnetic field facility and studied the light-harvesting complex PC645 from a cryptophyte algae where strongly coupled chromophores form molecular exciton states. We detected a change in high-frequency coherent oscillations when the field was engaged. Quantum chemical calculations coupled with a vibronic model explain the experiment as a magnetic field-induced shift of the exciton states, which in turn affects the electronic-vibrational resonance between pigments within the protein. Our results demonstrate the delicate sensitivity of interpigment coherent oscillations of vibronic origin to electronic-vibrational resonance interactions in light-harvesting complexes.

Ring currents modulate optoelectronic properties of aromatic chromophores at 25 T

“…For this study we developed a unique optical spectroscopy setup at the National High Magnetic Field Facility using the 25-T Split-Florida Helix magnet with the construction of a home-built broadband transient absorption setup around it (shown schematically in Fig. 1), described in our previous work (32). Phthalocyanines, which are cyclic organic chromophores (Fig.…”

Harnessing deep neural networks to solve inverse problems in quantum dynamics: machine-learned predictions of time-dependent optimal control fields

“…Specifically, our dataset was created by randomly sampling each of the parameters with the following ranges: amplitude A ∈ [1,10], center µ ∈ [-3, 3], and width ∆ ∈ [0. 5,2]. As such, each potential function can be fully described by nine randomly generated parameters.…”

“…In the context of molecular systems, the field of quantum optimal control 1 seeks to steer a chemical system from a known initial state to a desired target state via an external field, E(t), typically a tailored electromagnetic pulse. Predicting the explicit time-dependence of E(t) is central to providing critical initial conditions for experiments across multiple chemical physics domains including lightharvesting complexes, [2][3][4][5][6] quantum information processing, [7][8][9] laser cooling, 10,11 and ultracold physics. 12,13 As such, the capability to fully harness these optically-driven systems has tremendous potential to grow as we understand how to control the excited-state quantum dynamical processes that govern these systems.…”

Optical Activity from the Exciton Aharonov–Bohm Effect: A Floquet Engineering Approach

“…Owing to the periodicity of the laser-driving, we employ Floquet theory 13,14 to calculate the spectral properties of the laser-driven system according to a recently developed methodology 15 . These Floquet engineering concepts are complementary to recent efforts using strong magnetic fields to dramatically alter the vibronic structure and consequently the optical properties of molecular aggregates, such as in the excited vibronic structure of light harvesting complexes in cryptophyte algae 16 , as well as to the design of topologically nontrivial phases in organic excitonic systems 17 . In particular, our study highlights the simplicity with which large values of excitonic AB phases can be obtained in nanoscale systems (as shown below, with weak laser intensities), in contrast with the difficulty associated with the giant magnetic fields that must be present for a nanoring to generate similarly large values of electronic AB phases.…”