Vibronic origin of long-lived coherence in an artificial molecular light harvester

Abstract

Natural and artificial light-harvesting processes have recently gained new interest. Signatures of long-lasting coherence in spectroscopic signals of biological systems have been repeatedly observed, albeit their origin is a matter of ongoing debate, as it is unclear how the loss of coherence due to interaction with the noisy environments in such systems is averted. Here we report experimental and theoretical verification of coherent exciton–vibrational (vibronic) coupling as the origin of long-lasting coherence in an artificial light harvester, a molecular J-aggregate. In this macroscopically aligned tubular system, polarization-controlled 2D spectroscopy delivers an uncongested and specific optical response as an ideal foundation for an in-depth theoretical description. We derive analytical expressions that show under which general conditions vibronic coupling leads to prolonged excited-state coherence.

Resolving Vibrational from Electronic Coherences in Two-Dimensional Electronic Spectroscopy: The Role of the Laser Spectrum

“…The selection of specific pathways through two-color experiments has also been described [49][50][51], but the concept that some vibronic signatures may be missing in one-color experiments, as described here, was previously only briefly noted by Butkus et al [52]. Recently, there have been efforts to model excitonic systems with the inclusion of vibrational coupling, giving rise to more complex energy level structures [53], which were experimentally verified in an artificial light harvesting complex whose structure proved especially convenient for rigorous polarization experiments [54]. For the study of other complex systems, our results demonstrate that explicit inclusion of the laser spectrum is essential for rigorous design and interpretation of 2D-ES experiments, and show how the laser spectrum can be used as a tool to fully benchmark ground-state coherences.…”

Coherent exciton dynamics in a dissipative environment maintained by an off-resonant vibrational mode

“…In particular, the importance of structured environments in the dynamics and coherence of open quantum systems is now beginning to be recognized. For example, a series of recent theoretical [5][6][7][8][9][10][11][12] and experimental [13][14][15][16] studies has provided strong evidence that strongly coupled discrete molecular vibrations play a significant role in the speed, efficiency, and quantum coherence of energy transfer in photosynthetic and other molecular systems. In a different context, the high degree of control and precision possible in artificial nanosystems has enabled experimental measurement and engineering of noise spectral densities in condensed matter systems.…”

Quantum dynamics of a vibronically coupled linear chain using a surrogate Hamiltonian approach

“…In such photophysical processes there is often strong mixing between the electronic and vibrational degrees of freedom (DOF) and the vibronic coupling between the electronic and nuclear DOFs can play a significant role. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] It has been reported that vibronic coupling is the origin of long-lived oscillations observed in two dimensional (2D) electronic spectra of the light-harvesting Fenna-Matthews-Olson (FMO) complex, 1-3 the photosystem II reaction centre, 4,5 an artificial molecular light harvester, 6 and a homodimer system. 7 Electronic resonance with vibrations has been suggested to enhance efficient photosynthetic energy transfer 10,17,18 and charge separation rate in oxygenic photosynthesis.…”