Synthesis, Structure, and Photophysical/Chiroptical Properties of Benzopicene-Based π‑Conjugated Molecules

The convenient synthesis of substituted
benzopicenes and azabenzopicenes
has been achieved by the cationic rhodium­(I)/H8–BINAP
or BINAP complex-catalyzed [2+2+2] cycloaddition under mild conditions.
This method was applied to the synthesis of benzopicene-based long
ladder and helical molecules. The X-ray crystal structure analysis
revealed that the benzopicene-based helical molecule is highly distorted
and the average distance of overlapped rings is markedly shorter than
that in the triphenylene-based helical molecule. Photophysical and
chiroptical properties of these benzopicene and azabenzopicene derivatives
have also been examined. With respect to photophysical properties,
substituted benzopicenes and azabenzopicenes showed red shifts of
absorption and emission maxima compared with the corresponding triphenylenes
and azatriphenylenes. With respect to chiroptical properties, the
CPL spectra of the benzopicene-based helical molecule showed two opposite
peaks, and thus the value of the CPL was smaller than that of the
triphenylene-based helical molecule presumably due to the presence
of two chiral fluorophores.