Two-photon excited fluorescence from higher electronic states of chlorophylls in photosynthetic antenna complexes: a new approach to detect strong excitonic chlorophyll a/b coupling.
Stepwise two-photon excitation of chlorophyll a and b in the higher plant main light-harvesting complex (LHC II) and the minor complex CP29 (as well as in organic solution) with 100-fs pulses in the Q(y) region results in a weak blue fluorescence. The dependence of the spectral shape of the blue fluorescence on excitation wavelength offers a new approach to elucidate the long-standing problem of the origin of spectral "chlorophyll forms" in pigment-protein complexes, in particular the characterization of chlorophyll a/b-heterodimers. As a first result we present evidence for the existence of strong chlorophyll a/b-interactions (excitonically coupled transitions at 650 and 680 nm) in LHC II at ambient temperature. In comparison with LHC II, the experiments with CP29 provide further evidence that the lowest energy chlorophyll a transition (at approximately 680 nm) is not excitonically coupled to chlorophyll b.
Leupold
Dieter
D
Max-Born-Institut für Nichtlineare Optik und Kurzzeitspektroskopie, D-12489 Berlin, Germany. leupold@mbi-berlin.de
Teuchner
Klaus
K
Ehlert
Jürgen
J
Irrgang
Klaus-Dieter
KD
Renger
Gernot
G
Lokstein
Heiko
H
D001426:Bacterial Proteins; D002734:Chlorophyll / Q000737:chemistry*; D000077194:Chlorophyll A; D019281:Dimerization; D008027:Light; D045342:Light-Harvesting Protein Complexes; D017785:Photons; D010788:Photosynthesis; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry*; D045332:Photosystem II Protein Complex; D013050:Spectrometry, Fluorescence; D013696:Temperature
D001426:Bacterial Proteins; D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; C023693:protein complex B800-850, Rhodobacter; D002734:Chlorophyll; C037184:chlorophyll b; D000077194:Chlorophyll A