Supramolecular Organogelation of Bacteriochlorophyll-c Possessing an Isobutyl Substituent at the 8-Position in Carbon Tetrachloride.

The supramolecular organogelation of bacteriochlorophyll(BChl)-c carrying an isobutyl substituent at the 8-position was observed in carbon tetrachloride at a concentration of about 10 mm at room temperature. The BChl-c gel was evaluated by several spectroscopic measurements: the electronic absorption spectrum exhibited a far-red shift of the Qy-absorption from 660 to 748 nm and the FTIR spectrum showed a shorter frequency shift of the 13-C=O stretching from 1683 to 1643 cm-1 compared to the shifts of the corresponding monomer solution in tetrahydrofuran. These observations strongly indicate that the gelating BChl-c molecules form self-aggregates that are reminiscent of light-harvesting chlorosomes of green photosynthetic bacteria. The present supramolecular organogel prepared from natural chlorophylls is promising for the creation of an intelligent soft material involving artificial photosynthesis.