Michal Gala PhD Thesis Defense

Michal Gala
PhD Candidate
Chemical Engineering
Academic advisor: Professor Zhenan Bao

Abstract: "Helicenes have long attracted attention as chiral conjugated molecules with intriguing optical, electronic, and structural properties. Their helical geometry makes them promising candidates for chiral optoelectronics, spin-selective materials, and other technologies that couple molecular structure with light, charge, and spin. Despite this promise, helicenes have often been studied primarily as molecular chromophores rather than as practical components of electronic materials. This gap arises in part from synthetic challenges that can limit structural tunability, scalability, and integration into the molecular architectures commonly used in organic semiconductors. This dissertation addresses these challenges by developing helicene-based building blocks and design strategies that translate molecular helicity into functional organic electronic materials.

The first part of this work focuses on the design and synthesis of scalable, electronically tunable helical building blocks for organic semiconductors. By combining helicene-derived molecular geometry with conjugated frameworks designed for electronic function, these materials provide access to chiral semiconducting motifs with adjustable energy levels and modular synthetic handles. This approach enables helicenes to be incorporated into new organic semiconductor architectures while preserving the structural features that make them attractive for chiral materials design.

The second part of this dissertation explores how helical motifs can be covalently integrated into polymeric semiconductor systems. In these materials, helicene incorporation provides a strategy for introducing controlled nonplanarity and helicity into otherwise more conventional conjugated backbones. Systematic variation of helicene content reveals how molecular geometry influences thin-film organization, mechanical properties, charge transport, and optical response. These studies show that helical, nonplanar motifs can be incorporated into processable semiconducting materials while maintaining key features required for functional electronic systems.

Finally, we investigate how molecular chirality is amplified through supramolecular organization in the solid state. While helicenes are intrinsically chiral at the molecular level, their chiroptical behavior in semiconducting materials depends strongly on how that chirality is expressed after assembly. Through control of molecular design and solid-state organization, this dissertation demonstrates pronounced circular dichroism and circularly polarized luminescence in helicene-based materials. These results show that chiroptical function can be tuned not only through molecular structure, but also through the organization of molecules in the condensed phase. More broadly, this work connects molecular helicity with emergent optical activity in functional organic semiconductor materials.

Overall, this dissertation establishes helicenes as scalable and modular components for organic semiconductor design. By connecting synthesis, molecular structure, solid-state organization, mechanical behavior, charge transport, and chiroptical function, this work expands the toolbox for designing chiral electronic materials and points toward future applications in circularly polarized optoelectronics and molecular spintronics."