Synthesis and Characterization of Amphiphilic Phenylene Ethynylene Oligomers and Their Langmuir-Blodgett Films

We report the synthesis of a series of amphiphilic molecular building blocks that can be self-assembled at the air−water interface to form two- and three-dimensional nanostructures with tunable optoelectronic properties. Compression of these molecular building blocks using the Langmuir−Blodgett method gives rise to monolayer and multilayer thin films with different packing densities and electronic properties that are tunable due to varying π−π (hydrophobic) interactions. Depending on the noncovalent interaction between chromophores, we observe a transition toward denser packing with increasing number of phenylene ethynylene repeat units. Additionally, we use quantum-chemical simulations to help determine the excited-state electronic structure, intermolecular interactions, and packing trends. Our results demonstrate that the interplay between dipole−dipole and π−π interactions dominates the formation of thin films with various packing densities and determines the associated optical properties.