Azahelicene-containing arenes: Synthesis, crystal analyses, photophysics and optical limiting properties

A novel azahelicene-containing arene 4a, along with the preferential formed compound 3 have been synthesized via the Scholl reaction of the precursor 2 in the presence of triflic acid and different amount of DDQ. Their molecular structures were determined via single crystal X-ray diffraction, where compounds 4a containing two (Wu et al., 2017) [5]helicene unit and 3 containing one (Wu et al., 2017) [5]helicene unit exhibit offset packing model including two isomers. The former 4a can pile up into a one-dimensional configuration and the latter 3 aggregates into a sandwich packing model. Compounds 2, 3, 4a emit strong blue, yellow and orange light, respectively along with the successive ring reconstruction. Compound 4a displays nonlinear optical property measured via open-aperture Z-scan method and its optical limiting performance is prior to that of the state-of-the-art material C₆₀.