Synthesis of novel regioisomeric phenanthro[a]phenazine derivatives through the SNAr strategy and their self-assembly into columnar phases

Abstract

The cyclocondensation reaction of triphenylene-1,2-diquinone with 1,2-diamino-4-nitrobenzene results in two regioisomers, and is succeeded by a nucleophilic substitution reaction with alkyl mercaptans. The synthesis of unsymmetrically substituted phenazines, separation and characterization of their regioisomers are rare in discotic liquid crystal chemistry. Here, we report for the first time the synthesis of two regioisomers of phenanthro[a]phenazine via a simple S_NAr substitution reaction. Separation of these regioisomers was achieved successfully via column chromatography and they were well characterized by spectroscopic analysis. Both the regioisomers were found to be mesomorphic. This study throws a lot of light on the S_NAr strategy for functionalizing diverse π-conjugated systems for various applications.