Linke, M; Lauer, A; von Haimberger, T; Zacarias, A; Heyne, K

JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 2008, 130(45), p. 14904-14905

Chlorophyll a (Chl a) is the most abundant pigment on earth. In all plants, algae, and cyanobacteria, it plays a pivotal role as an antenna and reaction center pigment in the primary steps of photosynthesis. In the past, a true three-dimensional (3D) experimental determination of the Q_y electronic transition dipole moment orientation could not be obtained. With combined femtosecond polarization resolved VIS pump-IR probe experiments and theoretical calculations of the infrared transition dipole moments (tdm's) in the electronic ground state, we determined the 3D orientation of the Q_y electronic tdm of Chl a within the molecular structure. Polarization resolved experiments provided angles of the Q_y electronic tdm with three different infrared tdm's, whose orientations within the molecular structure were taken from our theoretical calculations. The orientation of the Q_y tdm results from the intersection of all three angles and was found to have an angle of (78 ± 3)degrees with the x-axis, (12 ± 3)degrees with the y-axis, and (86 ± 2)degrees with the z-axis.

DOI 10.1021/ja804096s