Two-dimensional spectroscopy of a molecular dimer unveils the effects of vibronic coupling on exciton coherences.
Alexei Halpin, Philip J M Johnson, Roel Tempelaar, R Scott Murphy, Jasper Knoester, Thomas L C Jansen, R J Dwayne Miller
Author Information
Alexei Halpin: Institute for Optical Sciences and Departments of Chemistry and Physics, University of Toronto, 80 St George Street, Toronto, Ontario M5S 3H6, Canada.
Philip J M Johnson: Institute for Optical Sciences and Departments of Chemistry and Physics, University of Toronto, 80 St George Street, Toronto, Ontario M5S 3H6, Canada.
Roel Tempelaar: Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands.
R Scott Murphy: Department of Chemistry and Biochemistry, University of Regina, 3737 Wascana Parkway, Regina, Saskatchewan S4S 0A2, Canada.
Jasper Knoester: Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands.
Thomas L C Jansen: Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands.
R J Dwayne Miller: 1] Institute for Optical Sciences and Departments of Chemistry and Physics, University of Toronto, 80 St George Street, Toronto, Ontario M5S 3H6, Canada [2] Max Planck Institute for the Structure and Dynamics of Matter, Atomically Resolved Dynamics Division, Building 99 (CFEL), Luruper Chaussee 149, 22761 Hamburg, Germany.
The observation of persistent oscillatory signals in multidimensional spectra of protein-pigment complexes has spurred a debate on the role of coherence-assisted electronic energy transfer as a key operating principle in photosynthesis. Vibronic coupling has recently been proposed as an explanation for the long lifetime of the observed spectral beatings. However, photosynthetic systems are inherently complicated, and tractable studies on simple molecular compounds are needed to fully understand the underlying physics. In this work, we present measurements and calculations on a solvated molecular homodimer with clearly resolvable oscillations in the corresponding two-dimensional spectra. Through analysis of the various contributions to the nonlinear response, we succeed in isolating the signal due to inter-exciton coherence. We find that although calculations predict a prolongation of this coherence due to vibronic coupling, the combination of dynamic disorder and vibrational relaxation leads to a coherence decay on a timescale comparable to the electronic dephasing time.
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