The two indolocarbazoles 2 and 4 were synthesized via the reductive ring closure of dinitrodiphenylbenzenes with triethylphosphite as reducing agent in a high boiling solvent. The electrochemical behaviour of the title systems is discussed.

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+ Present address: BASF AG, D-67056 Ludwigshafen, FRGThe synthesis and the optical properties of the novel polymer polyphenothiazinobisthiazole (PPT) are described. The design of this polymer was planned taking into consideration several aspects that were anticipated to lead to a material with an enhanced nonlinear optical susceptibility Monomer 16 was prepared in a five-step synthesis starting from N-dodecyl-3,7-diaminophenothiazin (11). 16 was reacted with terephthaloyl chloride to yield the precursor polyamide 17.This precursor polyamide was subjected to a thermal cyclization at 300 OC under vacuum leading to the title polymer PPT (18).PPT shows UVIvis absorption maxima at 1 =282 nm,305 nm and 463 nm.The macroscopic nonlinear optical suscepti-bility~'~)(-3w; w, w, w ) of a thin film ofPPTwas determined with a third harmonic generation (THG) technique at a fundamental laser wavelength 1,. = 1064 nm. The results show that PPT exhibits nonlinear optical properties comparable to those of poly-p-phenylenevinylene (PPV).