title: Laser-Limited Signatures of Quantum Coherence.
abstract: Quantum coherence is proclaimed to promote efficient energy collection by light-harvesting complexes and prototype organic photovoltaics. However, supporting spectroscopic studies are hindered by the problem of distinguishing between the excited state and ground state origin of coherent spectral transients. Coherence amplitude maps, which systematically represent quantum beats observable in two-dimensional (2D) spectroscopy, are currently the prevalent tool for making this distinction. In this article, we present coherence amplitude maps of a molecular dimer, which have become significantly distorted as a result of the finite laser bandwidth used to record the 2D spectra. We argue that under standard spectroscopic conditions similar distortions are to be expected for compounds absorbing over a spectral range similar to, or exceeding, that of the dimer. These include virtually all photovoltaic polymers and certain photosynthetic complexes. With the distortion of coherence amplitude maps, alternative ways to identify quantum coherence are called for. Here, we use numerical simulations that reproduce the essential photophysics of the dimer to unambiguously determine the excited state origin of prominent quantum beats observed in the 2D spectral measurements. This approach is proposed as a dependable method for coherence identification.
authors.affiliation: Zernike Institute for Advanced Materials, University of Groningen , Nijenborgh 4, 9747 AG Groningen, The Netherlands.
authors.forename: Roel
authors.initials: R
authors.lastname: Tempelaar
authors.affiliation: Institute for Optical Sciences and Departments of Chemistry and Physics, University of Toronto , 80 St. George Street, Toronto, Ontario M5S 3H6, Canada.
authors.forename: Alexei
authors.initials: A
authors.lastname: Halpin
authors.affiliation: Institute for Optical Sciences and Departments of Chemistry and Physics, University of Toronto , 80 St. George Street, Toronto, Ontario M5S 3H6, Canada.
authors.forename: Philip J M
authors.initials: PJ
authors.lastname: Johnson
authors.affiliation: Department of Chemistry and Biochemistry, University of Regina , 3737 Wascana Parkway, Regina, SK S4S 0A2, Canada.
authors.forename: Jianxin
authors.initials: J
authors.lastname: Cai
authors.affiliation: Department of Chemistry and Biochemistry, University of Regina , 3737 Wascana Parkway, Regina, SK S4S 0A2, Canada.
authors.forename: R Scott
authors.initials: RS
authors.lastname: Murphy
authors.affiliation: Zernike Institute for Advanced Materials, University of Groningen , Nijenborgh 4, 9747 AG Groningen, The Netherlands.
authors.forename: Jasper
authors.initials: J
authors.lastname: Knoester
authors.affiliation: Institute for Optical Sciences and Departments of Chemistry and Physics, University of Toronto , 80 St. George Street, Toronto, Ontario M5S 3H6, Canada.
authors.forename: R J Dwayne
authors.initials: RJ
authors.lastname: Miller
authors.affiliation: Zernike Institute for Advanced Materials, University of Groningen , Nijenborgh 4, 9747 AG Groningen, The Netherlands.
authors.forename: Thomas L C
authors.initials: TL
authors.lastname: Jansen
mesh_terms: D002232:Carbocyanines / Q000737:chemistry; D019281:Dimerization; D007834:Lasers; D008958:Models, Molecular; D008968:Molecular Conformation; D011789:Quantum Theory
chemical_list: D002232:Carbocyanines