Vibronic Enhancement of Algae Light Harvesting Jacob C. Dean, Tihana Mirkovic, Zi S.D. Toa, Daniel G. Oblinsky, Gregory D. Scholes  Chem  Volume 1, Issue 6, Pages 858-872 (December 2016) DOI: 10.1016/j.chempr.2016.11.002 Copyright © 2016 Elsevier Inc. Terms and Conditions

Chem 2016 1, 858-872DOI: (10.1016/j.chempr.2016.11.002) Copyright © 2016 Elsevier Inc. Terms and Conditions

Figure 1 Steady-State Spectroscopy, Pigment Architecture, and Active Coherences in PC645 (A) Absorption (black, solid) and fluorescence (red) spectra of PC645 at ambient temperature and absorption spectrum at 77 K (black, dashed) with estimated pigment absorptions shown as sticks. The laser pulse spectrum is also shown (blue, shaded). (B) Crystal structure of PC645; the pigments are color coded on the basis of their approximate order in the absorption spectrum: phycocyanobilin (PCB), red; mesobiliverdin (MBV), yellow-green; and dihydrobiliverdin (DBV), blue. (C and D) Fourier-transformed spectrum of oscillatory broadband transient absorption signal (C), where orange, red, blue, and green regions denote CH wag, CH/NH bending and C–C/C–N stretching, C=NH stretching, and C=C stretching regions, respectively (D). Dashed lines indicate PCB and DBV– transition energies at 77 K. Chem 2016 1, 858-872DOI: (10.1016/j.chempr.2016.11.002) Copyright © 2016 Elsevier Inc. Terms and Conditions

Figure 2 2D Spectroscopy of PC645 2D spectra taken at 295 K (A) and 77 K (B) at selected population times and (C) the anti-diagonal evolution through dihydrobiliverdin and phycocyanobilin cross-peaks. Dashed lines indicate PCB82 and DBV– transition energies at 77 K. Chem 2016 1, 858-872DOI: (10.1016/j.chempr.2016.11.002) Copyright © 2016 Elsevier Inc. Terms and Conditions

Figure 3 2D Coherence Maps and Vibronic Coupling in PC645 (A) Rephasing and non-rephasing coherence maps for ν2 = 1,600 cm−1 at 77 K. (B and C) Simulated coherence maps for (B) 1,580 cm−1 vibrational coherence of PCB and (C) vibronic coherence formed from mixing PCB (n = 1) and DBV (n = 0). The vibronic map is for the upper vibronic state containing nominally more PCB character. (D) Energy-level diagram depicting vibrational coherence localized on the PCB pigment (left) used as the model for simulations shown in (B); coherence is generated on both the PCB ground and excited states. The diagram on the right depicts vibronic coupling between the PCB and DBV pigments used as the basis for simulations shown in (C); coherence can be generated between a vibronic state and the PCB zero-point level (vibronic coherence) or on the ground state relayed and amplified through a vibronic state. Chem 2016 1, 858-872DOI: (10.1016/j.chempr.2016.11.002) Copyright © 2016 Elsevier Inc. Terms and Conditions

Figure 4 Vibronic Coupling Enhances the Rate of Energy Transfer (A) The Förster rate as a function of energetic detuning between DBV and PCB for J = 38 cm−1. The inset shows the basis spectra for acceptor absorption (red) and donor fluorescence (blue) along with the spectral overlap (black) at 1,310 cm−1. Dashed arrows represent spectroscopic changes when vibronic intensity borrowing is considered. (B) The enhancement of the DBV-to-PCB energy-transfer rate due solely to vibronic coupling is plotted as a function of the resonance between the vibrational frequency, hν = 1,580 cm–1, and the energy gap between the DBV and PCB transitions, E0. The right plots show crude adiabatic potentials and calculated vibronic densities in the excited electronic states. We used a dimensionless displacement of 0.4 and electronic coupling of 80 cm–1 (red circles) and 40 cm–1 (black circles). Chem 2016 1, 858-872DOI: (10.1016/j.chempr.2016.11.002) Copyright © 2016 Elsevier Inc. Terms and Conditions