The aggregation behavior of synthetic zinc-8 1 -hydroxy-chlorins in nonpolar organic media and in solid thin film has been compared with that of zinc-3 1 -hydroxy-chlorin, a model of bacteriochlorophyll-d in the chlorosomes of green photosynthetic bacteria. Zinc-8 1 -hydroxy-13 1oxo-and 3 1 ,13 1 -dioxo-chlorins 1a and 3a self-aggregate in nonpolar organic solvents and in solid thin films. They show less red-shifted and wider visible absorption bands at the Soret and Q y regions and also more intense circular dichroism (CD) signals at the Soret region than self-aggregates of zinc-3 1 -hydroxy-13 1 -oxo-chlorin 5a. The 1 H-NMR spectroscopic data indicate that the hydroxyl group at the 8 1 -position of 1a coordinates with the central zinc of an adjacent molecule in the supramolecule. From the infrared spectra, we can deduce that the interactions of the functional groups of 1a in the aggregates are unspecific or weak. For this reason, the supramolecular structures are partially amorphous. Visible absorption and CD spectra establish that the lack of one of the three interactive moieties (8 1 -hydroxy, 13-keto groups and central zinc) suppresses the aggregation ability of chlorins. Furthermore, zinc-3-acetyl-8 1 -hydroxy-chlorin 2a does not self-aggregate in nonpolar organic solvents because both the hydroxyl and keto groups take various configurations. However, additional substitution of keto carbonyl group at the 3-position (1aβ’3a) affects the aggregation ability. It is concluded that the fixation of either the OH or C_O group to the chlorin moiety possessing an exo-five-membered ring, as well as both the presence of OH, C_O and central metal in the molecule and the linear location of the three interactive moieties are necessary for the formation of well-ordered self-aggregates of chlorophyll analogues, which are seen in native chlorosomes.