THERMAL AND PHOTODEGRADATION OF PHOTOCHROMIC SPIROINDOLINENAPHTHOOXAZINES AND SPIROINDOLINENAPHTHOPYRANS - REACTION WITH NUCLEOPHILES - TRAPPING OF THE MEROCYANINE ZWITTERIONIC FORM

Adducts of the zwitterionic (ZW) form of merocyanine (MC) of five phot ochromic spirooxazines (SO) and spiropyrans (SP) have, for the first t ime, been prepared photochemically or thermally through a trapping rea ction of metastable MC with trimethylsilyl cyanide (TMSCN) in dichloro methane. The adducts (ZWAs) form easily and are obtained in almost qua ntitative yields. X-ray diffraction analysis of ZWA of spirooxazine 2 shows that in the adduct the planes of the indolyl and naphthyl moieti es form a ca. 29 degrees angle. The adduct crystallizes in the monocli nic space group P2(1)/n with a = 22.663(4) Angstrom, b = 8.234(1) Angs trom, c = 14.455(2) Angstrom, beta = 104.72(1)degrees, V = 2637.4(7) A ngstrom(3), and D-calcd = 1.1476 Mg/m(3) for Z = 4. Least-squares refi nement of the model based on 1986 reflections (F > 4 sigma(F)) converg ed to a final R = 0.066 and R-W = 0.068. ZWAs form through an unpreced ented, clean, and regioselective Michael-type 1,6-addition of TMSCN to either a strongly polarized quinoidal MC form or its charge-separated zwitterionic limit structure. No evidence for the more common 1,2- an d/or 1,4-addition has been found. The observed high reactivity of SOs and SPs with nucleophiles may contribute to the reported limited durab ility of these classes of photochromes.