Effect of the naphthylene linker on the J-aggregation abilities of chlorophyll-a derivatives.

Chlorophyll(Chl)-a derivatives inserting an ethynylene-naphthylene linker between the chlorin π-skeleton and hydroxymethyl group were prepared as models of chlorosomal Chls. Their syntheses were achieved via Sonogashira coupling reaction. Their J-aggregation behaviors were investigated by electronic absorption and circular dichroism spectroscopic measurements. These studies revealed that the 2,6-naphthylene inserted Chl-a derivatives gave the single J-aggregation species in an aqueous Triton X-100 micellar solution with a larger red-shift value (1270 cm) of the Qy band in spite of its longer linker compared with p-phenylene inserted Chl-a derivative (970 cm). These unique optical properties were also discussed based on the computational studies, which indicated the different positional relation of chlorin rings in the assemblies by the linker structure.