Synthesis and charge transfer complexation of chiral polynitrohelicenes

1,12-Dimethylbenzo[c]phenanthrene-5,8-dinitrile is nitrated at symmetrical positions giving 2,11-dinitro-, 4,9-dinitro, and 2,4,9,11-tetranitrohelicenes depending on the reaction conditions. The electron-deficient helicenes form charge-transfer (CT) complexes with pyrene in the solution as well as in the solid state. Crystal of the CT complex obtained from either (P)- or (+/-)-tetranitrohelicene possesses columnar structure but with different helicity, diameter, and pitch.