As the key hydrophobic unit in the molecular structure, alkyl chain building blocks have no strong interaction with the conjugated structure, so they do not affect the electronic properties of the molecule. The solubility and dispersion of the molecules in aqueous and organic solvents can be regulated to enhance the processability in the solution state through the hydrophobic properties of the hydrocarbon chain segments and the intermolecular interaction. The long alkyl chain forms an ordered solvation layer through the hydrophobic effect, which reduces the intermolecular attraction and improves the solubility in non-polar media. In polar solvents, due to the hydrophobic effect, the molecular aggregation is enhanced and the solubility is reduced. In terms of steric hindrance, branched alkyl chains will destroy the molecular planarity to suppress the crystallization tendency and increase the proportion of amorphous state, enhancing the solubility in organic solvents. In aqueous systems, the strong hydrophobicity of alkyl chains drives hydrophobic aggregation of molecules to form micelles, vesicles, or lamellar structures to minimize the contact between the non-polar interface and water. The critical micelle concentration and micelle size are determined by the length of the alkyl chain and the degree of branching. The long linear chains lower the critical micelle concentration and promote the formation of large micelles due to the enhanced hydrophobicity.
In contrast, the branched chains increase the curvature of micelles to form smaller aggregates via steric hindrance. Therefore, the solubility and self-assembly tendency can be balanced by adjusting the length of the alkyl chains, so that the molecules can obtain both fat solubility and moderate water dispersibility. At the same time, the introduction of branched alkyl chains can break the close packing between chains to inhibit crystallization and significantly improve the solubility in hydrocarbon solvents.