文摘
Electron-phonon and electron-vibrational coupling strengths of a weakly (excitonically) coupled chlorophylla S1 S0 transition of the CP29 antenna complex of plant photosystem II were studied by differencefluorescence-line-narrowing spectroscopy at 4.5 K. A strong, almost linear increase of the electron-phononcoupling strength toward longer wavelengths was observed, with Huang-Rhys factors Sph increasing from0.41 ± 0.05 at 680 nm to about 0.66 ± 0.07 at 688 nm. The former and latter wavelengths are located closeto the peak and on the red edge of the inhomogeneous site distribution function, respectively. The experimentallyobtained wavelength dependence of Sph may originate either from an alteration of the electron-phonon couplingstrength by the local environment of the fluorescing chromophore and/or from the presence of two isoformsof CP29, which are characterized by different coupling strengths to the protein environment. The one-phononprofile peaks at m = 22 cm-1 and is described by an asymmetric function composed of a Gaussian low-energy wing and a Lorentzian high-energy tail with half-widths at half-maximum of 10 ± 1 and 60 ± 10cm-1, respectively. Thirty-nine individual vibrational modes between 90 and 1665 cm-1 were resolved, andtheir Huang-Rhys factors were determined, which fall in the range between 0.0004 and 0.032. The broadfeature present in the overlap region of phonon and vibrational modes at about 90 cm-1 is characterized byS = 0.048. An integral value of vibrational coupling strengths Svib = 0.36 ± 0.05 was determined, which issimilar to that observed earlier for the trimeric LHC II complex.