Estimation of Damped Oscillation Associated Spectra from transient absorption spectra in the PC612 cryptophyte antenna

Ivo H.M. van Stokkuma, Chanelle C. Jumperb, Joris J. Snellenburga, Greg D. Scholesc, Rienk van Grondellea, Pavel Malýa
aInstitute for Lasers, Life and Biophotonics, Faculty of Sciences, Vrije Universiteit Amsterdam, De Boelelaan 1081, 1081 HV Amsterdam, The Netherlands; bDepartment of Chemistry, University of Toronto, Toronto, Ontario M5S 3H6, Canada;  cDepartment of Chemistry, Princeton University, Washington Road, Princeton, New Jersey 08544, United States

When exciting the PC612 cryptophyte antenna with a 10 fs optical pulse, all eight bilin chromophores are excited (Arpin et al. (2015) Spectroscopic Studies of Cryptophyte Light Harvesting Proteins: Vibrations and Coherent Oscillations. The Journal of Physical Chemistry B 119 (31):10025-10034). The resulting superposition of electronically and vibrationally excited states evolves in time, which is monitored with transient absorption spectroscopy. We present a methodology to resolve simultaneously the contributions of the different electronically and vibrationally excited states from the complete data. The evolution of the vibrationally excited states is described with a superposition of damped oscillations. The amplitude of a damped oscillation cos(ωnt)exp(-γnt) as a function of the detection wavelength constitutes a Damped Oscillation Associated Spectrum DOASn(λ) with an accompanying phase characteristic φn(λ). The population dynamics is described by four lifetimes, with interchromophore equilibration in 0.8 and 7.5 ps. We have resolved 24 DOAS with frequencies between 130 and 1649/cm and with damping rates between 0.9 and 12/ps. In addition, 11 more DOAS with faster damping rates were necessary to describe the “coherent artefact”. The DOAS contain both ground and excited state features. Their interpretation is aided by DOAS analysis of simulated transient absorption signals resulting from stimulated emission and ground state bleach.

Figure: four selected DOAS with frequencies between 663 and 1585/cm, and damping rates between 0.9 and 3.0/ps. (A) species populations depicted until 0.3ps. The maximum of the IRF is at time zero. (B) estimated Species Associated Difference Spectra. In addition the negative of the steady state absorption (magenta) and emission (cyan) are plotted for reference. (C) superposition of four selected DOAS. (D and G) Cosine oscillations with frequencies ν (in /cm) and damping rates γ (in 1/ps) written in the legend at the left, using the appropriate color. (E and H) Estimated DOAS, color coded as in (D and G). (F and I) Accompanying phase profiles.