A novel domino protocol for three-component synthesis of new dibenzo[e,g]indoles: flexible intramolecular charge transfers

Fairly high yields of 2-aryl-3-nitrodibenzo[e,g] indoles were synthesized via a hitherto unreported domino-reaction of 9,10-phenanthrenequinone, ammonium acetate and beta-nitrostyrenes in one pot. This novel three-component synthetic route is efficaciously catalysed by the carboxylated multiwalled carbon nanotubes equipped with superparamagnetic amylose-coated magnetite nanoparticles. This reaction seems to proceed via a Robinson-like annulation of in situ generated phenanthrenequinone imine and presents a novel nitroolefin-based route for annulation of the indole ring. Our experiments display that the internal charge transfer between the aryl group and the indole nucleus of the products can be reversed based on the electronic nature of the aryl group and undergoes a wavelength shift in both absorption and fluorescence emission by changing the pH of the medium. These photophysical properties make the products interesting candidates for application in optoelectronic devices.