Zinc chlorophyll derivatives Zn-1-3 possessing a tertiary amino group at the C3 position have been synthesized through reductive amination of methyl pyropheophorbide-d obtained from naturally occurring chlorophyll-a. In a dilute CH Cl solution as well as in a dilute 10 %(v/v) CH Cl /hexane solution, Zn-1 possessing a dimethylamino group at the C3 position showed red-shifted UV/Vis absorption and intensified exciton-coupling circular dichroism (CD) spectra at room temperature owing to its dimer formation via coordination to the central zinc by the 3 -N atom of the dimethylamino group. However, Zn-2/3 bearing 3 -ethylmethylamino/diethylamino groups did not. The difference was dependent on the steric factor of the substituents in the tertiary amino group, where an increase of the carbon numbers on the N atom reduced the intermolecular N⋅⋅⋅Zn coordination. UV/Vis, CD, and H NMR spectroscopic analyses including DOSY measurements revealed that Zn-1 formed closed-type dimers via an opened dimer by single-to-double axial coordination with an increase in concentration and a temperature decrease in CH Cl , while Zn-2/3 gave open and flexible dimers in a concentrated CH Cl solution at low temperature. The supramolecular closed dimer structures of Zn-1 were estimated by molecular modelling calculations, which showed these structures were promising models for the chlorophyll dimer in a photosynthetic reaction center.

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Coordinated movements: A zinc chlorophyll‐a derivative possessing a dimethylamino group at the C31 position showed red‐shifted visible absorption and intensified exciton‐coupling circular dichroism (CD) spectra at room temperature owing to its dimer formation via coordination to the central zinc by the 31‐N atom, whereas its analogs bearing 31‐ethylmethylamino/diethylamino groups did not. The difference was dependent on the steric factor of the substituents in the tertiary amino group, in which an increase of the carbon numbers on the N atom reduced the intermolecular N⋅⋅⋅Zn coordination. UV/Vis, CD, and 1H NMR spectroscopic analyses including DOSY measurements revealed that Zn‐1 formed closed‐type dimers via an opened dimer by single‐to‐double axial coordination with an increase in concentration and a temperature decrease in CH2Cl2. More information can be found in the Full Paper by Hitoshi Tamiaki et al. on page 759 in Issue 7, 2017 (DOI: 10.1002/asia.201700015).