2025 Theses Doctoral

Dynamic Chirality in Perylene Diimide Nanoribbons

Bao, Si Tong

Helicenes, a class of polycyclic aromatic hydrocarbons (PAHs), are characterized by their twisted skeletons formed through ortho-annulated aromatic rings, leading to axial chirality and remarkable chiroptical properties. These features make helicenes promising candidates for advanced applications, including chiroptical nonlinear optics, asymmetric catalysis, and chiral switches. Perylene diimide (PDI), an electron-deficient PAH, is known for its exceptional optoelectronic properties and stability. Incorporating PDI units into helicene structures has emerged as an effective strategy for developing non-planar electron acceptors and molecules with enhanced chiroptical properties, making PDI-helicenes valuable for organic electronics and related fields.This thesis investigates the synthesis and chiroptical properties of PDI-[4]helicenes, presenting a method for controlling the dynamic axial chirality in PDI-based twistacenes. Chiral substituents at the imide position induce helicity within the structure, enabling the remote modulation of flexible [4] helicene subunits.

Additionally, a chiral molecular redox switch, chPDI[2], derived from PDI-based twistacenes, is introduced. This material demonstrates reversible multistate chiroptical switching across a broad wavelength range, including ultraviolet, visible, and near-infrared regions. Upon reduction, chPDI[2] shows a significant enhancement in its circular dichroic response, making it a promising candidate for chiroptical switching applications.

Finally, we explore chiral graphene nanoribbons (chGNRs) with acene-based cores, demonstrating helicity control in extended conjugated systems. The longest chGNR[40] exhibits one of the highest recorded chiroptical responses for organic molecules in the visible spectrum, offering new opportunities for chiral optoelectronics and molecular devices.