BIS(DICYANOMETHYLENE)-12-METHYLBENZO[B]PHENOXAZINE AND 6,11-DICYANIMINO-12-METHYLBENZO[B]PHENOXAZINE AS NOVEL DONOR-ACCEPTOR SYSTEMS

The novel, single-component donor-acceptor compounds bis(dicyanomethyl ene)-12-methylbenzo[b]phenoxazine (15) and 6,11-dicyanimino-12-methylb enzo[b]phenoxazine (17) have been prepared by treating N-methylbenzo [ b]phenoxazin-6,11-dione (14) with Lehnert's reagent and with N,N'-bis( trimethylsilyl)carbodiimide, respectively. The UV-VIS spectra of compo unds 15 and 17 present a broad, low-energy band in the red part of the visible spectrum which is assigned to an intramolecular charge transf er on the basis of molecular orbital calculations. Cyclic voltammetry shows that the DCNQI derivative, 17, gives rise to stable anions and d ianions, while the tetracyanoquinodimethane (TGNQ) derivative, 15, lea ds to the dianion through a two-electron reduction wave. Both compound s are observed to behave as good donors and accepters. The molecular s tructures of 15 and 17 have been investigated using the semiempirical PM3 method. This method predicts that both compounds are not planar, t he distortions from planarity being larger for 15. The changes induced by reduction on the molecular geometries provide evidence for a gain in the aromaticity of the acceptor moiety, which becomes planar, excep t for the anion of 15. This lack of planarity destablizes the anion an d explains the observation of a unique two-electron reduction wave for the dianion of 15.