6,11-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 6,11-bis(dicyanomethylene)-12-methylbenzo[b]phenoxazine (15) and 6,11-dicyanimino-12-methylbenzo[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 compounds 15 and 17 present a broad, low-energy band in the red part of the visible spectrum which is assigned to an intramolecular charge transfer on the basis of molecular orbital calculations. Cyclic voltammetry shows that the DCNQI derivative, 17, gives rise to stable anions and dianions, while the tetracyanoquinodimethane (TGNQ) derivative, 15, leads to the dianion through a two-electron reduction wave. Both compounds are observed to behave as good donors and accepters. The molecular structures of 15 and 17 have been investigated using the semiempirical PM3 method. This method predicts that both compounds are not planar, the 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, except for the anion of 15. This lack of planarity destablizes the anion and explains the observation of a unique two-electron reduction wave for the dianion of 15.