UC Berkeley

This dissertation focuses on the supramolecular self-assembly of organic semiconductor small molecules (SMs), polymers, and inorganic nanoparticles (NPs) for potential applications in solution processable optical, electronic, and stimuli-responsive devices. Highly crystalline, functional SMs have a number of desirable optical and electronic properties, but their strong tendency to aggregate makes it challenging to solution process them and optimize their morphology and macroscopic alignment in thin films. Block copolymers (BCPs) are readily solution processable and assemble into well-defined, nanoscopic arrays, desirable for a number of device applications. BCP-based supramolecules can be constructed by attaching functional SMs through secondary interactions, such as hydrogen bonding, to one or more blocks of a BCP. By this method, the advantages of these two materials can potentially be combined. However, the assembly of supramolecules based on highly crystalline SMs is less straightforward and has been less thoroughly investigated compared to their non-functional counterparts.

Macroscopically aligned, nanoscopic assemblies of organic semiconductors were achieved without hindering the electronic properties of the semiconductor by constructing organic semiconductor-based supramolecules. In bulk and thin films, a number of potentially useful morphologies for optical and electronic devices were formed by tuning the annealing conditions. The high degree of crystallinity of the SM was also found to greatly increase the BCP periodicity of the supramolecule and enhanced its thermally-responsive properties compared to supramolecules based on less crystalline SMs.

This led to an investigation of supramolecules based on two different families of SMs, where the composition of the crystalline core, the location (side- vs. end-functionalization) of the alkyl solubilizing groups, and the constitution (branched vs. linear) of the alkyl groups were varied. The crystallinity and packing of the SMs were identified as key parameters governing the overall assembly and packing of the supramolecules.

Supramolecules based on non-functional SMs have also been utilized as a template to direct the assembly of inorganic NPs through favorable interactions between the SMs and the NP ligands. Using organic semiconductor-based supramolecules as the template, the effects of the SM phase behavior as well as the NP size and loading rate on the assembly of supramolecular nanocomposites were investigated. While the assembly of these nanocomposites based on highly crystalline SMs was found to be distinct from both supramolecular nanocomposites based on less crystalline SMs and supramolecules based on highly crystalline SMs without NPs, nanostructured arrays of organic and inorganic semiconductors were obtained. These studies present a versatile method for the coassembly of polymers, highly crystalline functional SMs, and NPs for the fabrication of optical, electronic, and stimuli-responsive devices.