Synthetic substituted boronates of dihydroxy-bacteriochlorin absorbing and emitting far-red to near-infrared light as bacteriopheophytin-a analogs

Several substituted boronates of methyl cis-7,8-dihydroxy-pyrobacteriopheophorbide-a possessing the same 3-acetyl-13(1)-oxo-bacteriochlorin pi-conjugated system as bacteriopheophytin-a found in type-II reaction centers of anoxygenic photosynthetic bacteria were prepared by chemical modification of chlorophyll-a. The semisynthetic bacteriochlorins are less oxidizable to chlorins and more readily available from natural phototrophs than the above natural bacteriochlorin, while the formers show similar optical properties in solution as the latter. All the boronate pigments efficiently absorb near ultraviolet, green, and far-red light and strongly emit light in a far-red to near-infrared region. Their electronic absorption and fluorescence emission data are nearly independent of the alkyl and (hetero)aromatic substituents at the boron atom.