Supramolecular polymorphism in aggregates of a boron-difluoride complex of peri-naphthoindigo via solvent- and pathway-dependent self-assembly

Supramolecular polymorphism in dye aggregates and examples of N,O-bidentate boron difluoride complexes are very uncommon in chemistry. Both rarities have been addressed by synthesising a new N,O-bidentate boron difluoride complex PNIBF2, which shows polymorphic aggregation. Depending upon the nature of the solvent and preparation methods, PNIBF2 produced three different aggregates. In a non-polar environment, the dye produced emissive linear nanoaggregates Agg1. In contrast, in a polar solvent (76 : 24 v/v water-THF mixture), the dye produced two different types of cyclic aggregates, nanoellipsoids Agg2 and nanospheres Agg3. Kinetically controlled Agg2 were produced at room temperature, while Agg3 were generated at elevated temperatures. Supramolecular assemblies Agg2 could be readily converted into Agg3 by heating and subsequent slow cooling. Our results highlight the relevance of peri-naphthoindigo as a new molecular building block for the creation of functional supramolecular systems.