Diversity of dye aggregates: self-assembly of naphthalene-linked chlorophyll dyads dependent on substitution position

Chlorosomes, the light-harvesting antennae of green photosynthetic bacteria, exhibit supramolecular structural diversity arising from variations in the chemical structures of their constituent pigments. Although chlorosome models prepared via in vitro self-assembly of chlorophyll (Chl) derivatives have been extensively studied, their architectures, excluding tubular or fibrous structures, remain less explored. Here, we report the construction of supramolecular Chl aggregates with diverse morphologies through the self-assembly of various regioisomers of naphthalene-linked Chl dyads. These dyads were synthesized by amidative condensation of several naphthalenedicarboxylic acids with an aminated Chl-a derivative. Their self-assembly behavior was investigated by atomic force microscopy, as well as by UV-vis absorption and circular dichroism spectroscopy, demonstrating that the supramolecular morphology can be controlled by the substitution positions. Notably, highly symmetric Chl dyads linked with 1,5- and 2,6-naphthylene groups did not yield ordered aggregates, whereas some less symmetric dyads, including 1,7- and 2,7-substituted ones, formed well-ordered supramolecular architectures. This behavior contrasts with the general trend in supramolecular systems, in which highly symmetric molecules tend to form well-ordered assemblies. These findings provide insights into molecular design strategies for functional dye-based assemblies and contribute to the understanding of native chlorosomes.