Synthesis of carbazole derived aza[7]helicenes

Synthesis of four derivatives of symmetrical aza[7]helicenes is achieved by I2-THF mediated photocyclization of corresponding bis-styryl derivatives. The cyclization furnished the desired angularly fused aza-helicene in moderate yields. The structures are established by NMR spectroscopy and single crystal X-ray analysis for the difluoro derivative. The series of synthesized aza[7]helicenes showed remarkable thermal stability as indicated by DSC analysis.