Boost of Chiroptical Responses Through the Enhancement of Electron Transition Dipole Moment

The development of robust chiroptical systems is crucial for advancing optoelectronic technologies. Spirobifluorenes (SBFs) have proven to be versatile scaffolds for the construction of a wide variety of robust axially chiral compounds presenting strong chiroptical responses. Herein, we present a strategy for boosting the chiroptical responses via enhancing electric transition dipole moment (ETDM) of interacting chromophores in C₂-symmetric SBFs presenting exciton coupling. To experimentally validate this approach, we peripherally extended the SBF scaffold through Knoevenagel condensation with the aim of increasing the ETDM of the featured chromophores. The influence of the functionalization on the ETDM was investigated using a combination of computational modeling and experimental techniques, enabling a detailed examination of the relationship between molecular structure and chiroptical properties. Our results demonstrate that peripheral functionalization of SBFs significantly enhances the electric transition dipole moment (ETDM) of the constituent chromophores, with each incremental increase in ETDM resulting in a five-fold enhancement of the g-factor, thereby substantially amplifying the overall chiroptical activity. This straightforward strategy underscores the importance of the ETDM of interacting chromophores in fine-tuning the optoelectronic properties and provides a promising avenue for the rational design of high-performance chiroptical materials.