SYNTHESIS AND PROPERTIES OF DIETHYL 5,10-DIHETERA-5,10-DIHYDROINDENO[2,1-A]INDENE-2,7-DICARBOXYLATES

A series of six heterocyclic diesters lb-6b containing all combinations of nitrogen, sulfur, and selenium has been prepared from a common precursor, diethyl 2,2'-dinitrostilbene-4,4'-dicarboxylate. Electrochemical analysis showed oxidation potential increases in the order N < Se < S, and the same trend was observed for maxima of UV absorbance. Electrochemical oxidation of indoloindole lb (but not the other members of the series) generates a persistent radical cation whose properties were investigated. Diesters containing sulfur and selenium (but not nitrogen) form S(A) liquid crystals. A new synthetic method leading to the indolo[1,2-b]indazole ring system has been found.