Synthesis and photochemical study of substituted heterohelicenes and related compounds

Helicenes with aryl electron-withdrawing or/and electron-donating groups at one/both end/s are potential candidates for second order nonlinear optical applications. We have prepared such helicenes and related compounds. A single crystal X-ray structure showed the structure and architecture of 2,7-di-1-naphthylbenzo[1,2-b:4,3-b'] dithiophene to be racemic chiral helixes. Both terminal aryl rings contribute to the π-π stacking. Theoretically, there are two synthetic routes (A and B) for the synthesis of 2-(4-methoxylphenyl)trithia-[5]-heterohelicene and 2-(4-methoxylphenyl)-9-(4-cyanophenyl)trithia- [5]-heterohelicene. Although route A is more complicated, it is more efficient because substituents improve solubility. Introducing an electron-donating group increases the yields of all reactions in A.