Effects of Chlorophyll Triplet States on the Kinetics of Spectral Hole Growth

Abstract

Spectral hole burning has been employed for decades to study various amorphous solids and proteins. Triplet states and respective transient holes were incorporated into theoretical models and software simulating nonphotochemical spectral hole burning (NPHB) and including all relevant distributions, in particular the distribution of the angle between the electric field of light E and transient dipole moment of the chromophore μ. The presence of a chlorophyll a triplet state with a lifetime of several milliseconds explains the slowdown of NPHB (on the depth vs illumination dose scale) with the increase of the light intensity, as well as larger hole depths observed in weak probe beam experiments, compared to those deduced from the hole growth kinetics (HGK) measurements (signal collected at a fixed wavelength while a stronger burning beam is on) in cytochrome b6f and chemically modified LH2. We also considered the solvent deuteration effects on triplet lifetime and concluded that both triplet states and local heating likely play a role in slowing down the HGK with increasing burn intensity.

High-Resolution Frequency-Domain Spectroscopic and Modeling Studies of Photosystem I (PSI), PSI Mutants and PSI Supercomplexes

“…The generation of transient HB spectra requires the presence of a third, relatively long-lived state [34,37]. That is, the pigment transitions from the excited singlet state into a triplet state [106,107] or is converted photochemically to another long-lived (µs to ms range) product (e.g., a charge-separated state in the case of the RCs [37]), leaving a transient hole in the absorption spectrum with a ZPH at the excitation frequency (for resonant HB) and with the shape defined by the el-ph coupling parameters. In this case, the pigment's ground state is depopulated for the lifetime of the long-lived state, and the spectral hole will be observable only for the duration of this lifetime.…”