Synthesis and Chiroptical Properties of Biscarbazole-Embedded Diaza[7]helicenes

In this study, we report the synthesis and chiroptical properties of biscarbazole-embedded diaza[7]helicenes. Although the classical photocyclization pathway was unsuccessful, the strategic introduction of a bromo group successfully yielded the desired helical compounds. Interestingly, using methoxy groups instead of bromo groups led to the formation of an unusual degraded product during photocyclization. The synthesized molecules were resolved into their enantiomers, and their chiroptical properties were investigated by using steady-state absorption and emission spectroscopy. Additionally, the excited-state dynamics were examined through time-resolved fluorescence decay measurements. Quantum chemical calculations were performed to rationalize the observed optical properties.