Synthesis of bacteriochlorophyll-c analogs possessing thio-functionalized substituents at the 20-position and their self-aggregation

Methyl pyropheophorbides- a possessing some substituents at the 3-position as chlorophyll- a derivatives were regioselectively trifluoromethylthiolated and thiocyanated at the 20-position by heating with N -trifluoromethylthio- and thiocyanato-dibenzenesulfonimide, respectively, in N , N -dimethylformamide. Based on the novel thio-functionalization at the 20-position, zinc methyl 3-hydroxymethyl-pyropheophorbides- a bearing the 20-SCF 3 or SCN group were prepared as the models of naturally occurring bacteriochlorophyll(BChl)- c with the 20-Me group. The resulting model compounds self-aggregated in an aqueous Triton X-100 micellar solution to give red-shifted and broadened electronic absorption bands, similar to the self-aggregation of BChl- c in chlorosomes, major light-harvesting antennae of photosynthetic green bacteria. The electronic and steric effects of the 20-SX groups on the absorption bands of their monomeric and aggregated states as well as their self-aggregation abilities are discussed. • 20-Thio-functionalization of Chl- a derivatives successfully occurred by (PhSO 2 ) 2 NSX. • The regioselective substitution with SCF 3 and SCN bathochromically shifted Qy bands. • Synthetic BChl- c analogs self-aggregated in aqueous micelles similar to chlorosomes. • The chlorosome-like J -aggregation red-shifted and broadened Qy and Soret bands. • The self-assembly of 20-SCN model was more stable than its 20-SCF 3 counterpart.