Two-dimensional electronic spectroscopy of bacteriochlorophyll a with synchronized dual mode-locked lasers

Junwoo Kim,Tai Hyun Yoon,Jonggu Jeon,Minhaeng Cho

doi:10.1038/s41467-020-19912-5

Abstract

How atoms and electrons in a molecule move during a chemical reaction and how rapidly energy is transferred to or from the surroundings can be studied with flashes of laser light. However, despite prolonged efforts to develop various coherent spectroscopic techniques, the lack of an all-encompassing method capable of both femtosecond time resolution and nanosecond relaxation measurement has hampered various applications of studying correlated electron dynamics and vibrational coherences in functional materials and biological systems. Here, we demonstrate that two broadband (>300 nm) synchronized mode-locked lasers enable two-dimensional electronic spectroscopy (2DES) study of chromophores such as bacteriochlorophyll a in condensed phases to measure both high-resolution coherent vibrational spectrum and nanosecond electronic relaxation. We thus anticipate that the dual mode-locked laser-based 2DES developed and demonstrated here would be of use for unveiling the correlation between the quantum coherence and exciton dynamics in light-harvesting protein complexes and semiconducting materials.

Highlights

How atoms and electrons in a molecule move during a chemical reaction and how rapidly energy is transferred to or from the surroundings can be studied with flashes of laser light
Delocalized quantum excited states created by photoexcitation of and electronic couplings between light-absorbing chromophores relax through a myriad of pathways, such as exciton migration, excitation localization induced by the thermal fluctuation of coupled bath degrees of freedom, and long-distance Förster energy transfer[3,4,5]
This spatial interference fringe generated by the two pump fields propagating in the two different directions determined by the wave vectors of kA and kB acts like a grating

Summary

Introduction

How atoms and electrons in a molecule move during a chemical reaction and how rapidly energy is transferred to or from the surroundings can be studied with flashes of laser light. One of the most crucial techniques for studying such complex photoinduced reaction dynamics of generic self-assembled multichromophoric systems is two-dimensional electronic spectroscopy (2DES)[1,6,7,8], which is capable of providing the time correlation between the initial and final states by mapping their nonlinear optical response onto 2D excitation- and detection-frequency space[9,10]. The 2DES requires multiple femtosecond optical pulses to interrogate molecular systems, such as light-harvesting protein complexes[1,11,12,13,14], optical chromophores in solutions[10,15], semiconducting materials[16,17], metallic nanoparticles[18], and chiral aggregates[19] It provides information on ultrafast energy transfer kinetics and dephasing time scales of electronic and/or vibrational coherences of coupled chromophore systems like photosynthetic proteins[12,20]. In ASOPS, each ML generates a train of optical pulses separated by an equal time interval

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Results

Conclusion