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Updated: May 16, 2025
![Cercosporin-Photocatalyzed [4+1]- and [4+2]-Annulations of Azoalkenes Under Mild Conditions](/_next/image?url=https%3A%2F%2Fcloudfront.jove.com%2FCDNSource%2Fteasers%2F60786.jpg&w=3840&q=50)
Cercosporin-Photocatalyzed [4+1]- and [4+2]-Annulations of Azoalkenes Under Mild Conditions
Published on: July 17, 2020
Fluorescent Carbazole-Derived Aza[5]Helicenes: Synthesis, Functionalization, and Characterization
Inka Marten1, Melina E A Dilanas2, Joachim Podlech1
1Institute of Organic Chemistry, Karlsruhe Institute of Technology (KIT), Kaiserstraße 12, Karlsruhe, Germany.
Abstract:
5,8-Dihydroindolo[2,3-c]carbazole (ICz), 9H-cinnolino[3,4-c]carbazole (CnCz), and variously alkyl-, alkenyl-, and aryl-substituted indolo[2,3-k]- and -[3,2-a]phenanthridines (IPs) were synthesized using an ortho fusion strategy with Suzuki cross couplings, intramolecular nitrene insertions, diazo couplings, and Morgan-Walls cyclizations as key reactions. The IPs were additionally transformed into organoboranes and helicene conjugates with tetraphenylethylene derivatives. The compounds fluoresce with large Stokes shifts, exhibit strong acidochromism, and show a good to excellent aggregation-induced emission. Their helical structure was elucidated by x-ray crystallographic analysis and by quantum chemical calculations. HOMO-LUMO gaps of 3.96-4.06 eV and S1-T1 gaps were calculated, with CnCz showing a small singlet-triplet inversion. Relative pKa values of 6.65-9.55 were estimated for the different types of azahelicenes.
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