Combined Experimental and Computational Study of Polyaromatic Hydrocarbon Aggregation: Isolating the Effect of Attached Functional Groups

To establish, and isolate, the influence of different chemical functional groups on the aggregation of polyaromatic hydrocarbons, a series of triphenylene-based compounds were investigated using a combined experimental and computational approach. Containing alkoxy side chains of varying lengths or amide appendages, both with and without a terminating carboxylic acid, their aggregation structures, sizes, and kinetics in toluene were studied over several length scales, using a combination of dynamic light scattering and diffusion-ordered nuclear magnetic resonance spectroscopy, complemented with molecular dynamics simulations. There is a strong correlation between molecular architecture and aggregation mechanisms: the addition of polar functional groups and heteroatoms resulted in compounds that are more prone to aggregation and form large, micrometer-sized clusters, while the increased steric hindrance imposed by alkoxy side chains led to stable nanometer-sized aggregates. These conclusions underline the strong structure-function relationship of polyaromatic hydrocarbons, such as asphaltenes, examined here over multiple length scales in a single solvent. We also demonstrate the importance of using complementary techniques to study the aggregation process of polyaromatic hydrocarbons that could form aggregates of various sizes over different time scales.