Strongly coupled bacteriochlorin dyad studied using phase-modulated fluorescence-detected two-dimensional electronic spectroscopy

Abstract

Fluorescence-detected two-dimensional electronic spectroscopy (F-2DES) projects the third-order non-linear polarization in a system as an excited electronic state population which is incoherently detected as fluorescence. Multiple variants of F-2DES have been developed. Here, we report phase-modulated F-2DES measurements on a strongly coupled symmetric bacteriochlorin dyad, a relevant 'toy' model for photosynthetic energy and charge transfer. Coherence map analysis shows that the strongest frequency observed in the dyad is well-separated from the excited state electronic energy gap, and is consistent with a vibrational frequency readily observed in bacteriochlorin monomers. Kinetic rate maps show a picosecond relaxation timescale between the excited states of the dyad. To our knowledge this is the first demonstration of coherence and kinetic analysis using the phase-modulation approach to F-2DES.

Simulating Fluorescence-Detected Two-Dimensional Electronic Spectroscopy of Multichromophoric Systems

“…The experiments reported here were performed using the experimental setup reported in ref (14). Briefly, a white light continuum is generated by focusing the 1 MHz 1040 nm output of a tunable repetition rate laser amplifier (Spectra Physics, Spirit 1040-16) into a 4 mm YAG crystal, followed by selecting a part of the white light continuum using a combination of OD4 650 nm long pass and OD4 875 nm short pass optical filters (Edmund).…”

“…Briefly, a white light continuum is generated by focusing the 1 MHz 1040 nm output of a tunable repetition rate laser amplifier (Spectra Physics, Spirit 1040-16) into a 4 mm YAG crystal, followed by selecting a part of the white light continuum using a combination of OD4 650 nm long pass and OD4 875 nm short pass optical filters (Edmund). The resulting beam is collimated and routed into the experimental setup described in detail in ref (14). The collinear pulse train, precompressed to ∼15 fs using a SLM pulse shaper (MIIPS640P, Biophotonic Solutions), is reflected from a 875 nm dichroic mirror (Semrock) toward an air objective (Olympus LUCPlanFLN 40×, NA0.6) and is focused on the sample to a focal spot of full width at half-maximum (fwhm) ∼1.3 μm as determined by a fluorescence image of a 0.5 μm fluorescent bead (Fluoresbrite 763 Carboxylate Microspheres).…”

“…Recent F-2DES experiments 7,12,14 have reported early waiting time spectra of detergent-isolated LH2 exhibiting distinct positive cross-peaks, leading to the suggestion of unexpectedly large delocalization of the initial excitation. 12 Furthermore, the B850 band was reported to be round at early times in these experiments.…”

Rapid multiple-quantum three-dimensional fluorescence spectroscopy disentangles quantum pathways

“…Considering the relevance of this value for multiparticle interactions, however, we have to take into account the relative distance of chromophores because for systems that do not form aggregates (such as in the present case), the probability of bimolecular processes is generally low. According to the suggestion of Tiwari et al, we have estimated the effect of multiparticle interactions for the present sample using Förster resonance energy transfer (FRET) as a crucial step that would facilitate the interaction of populations of two distinct molecules by subsequent exciton–exciton annihilation 43 . We calculated the Förster critical concentration 74,75 for this effect to be 0.54 mM, which is above our concentration (0.40 mM) so that we expect such contributions in our experiment not to be present.…”

Phase-Modulated Rapid-Scanning Fluorescence-Detected Two-Dimensional Electronic Spectroscopy

“…The phase-modulation approach was pioneered by Marcus and coworkers and used for wave packet interferometry 12 as well as fluorescence-detected 9-10 and photocurrent-detected 13 two-dimensional electronic spectroscopy (2DES). Their approach has been adopted by a number of other groups for fluorescence-detected 2DES [14][15][16] and other action-based 2D measurements [17][18] .…”