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Semiconducting organometallic films such as copper tetracyanoquinodimethane (CuTCNQ) have been observed to switch between two stable states when exposed to optical radiation. Observations of switching between two states in these films have been made by Raman spectroscopic methods and direct observation of electrical resistance changes. Line or pattern generation is observed for exposure above certain threshold levels. These effects are observed in a wide range of Cu and Ag organometallic compounds.

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mi of the concept of aromaticity, which is itself somewhat an artifact of inadequate structural description, suggest that such designations are not presently justifiable.Consideration of tropone as formally related to benzene by carbonyl insertion of 2-and 4-pyrone as similarly related to furan shows that insertion of a carbonyl group into these aromatic rings drastically suppresses the contribution of nonlocal effects to the molecular magnetic susceptibility.Extrapolation of these results beyond the present studies raises the questions of whether formal carbonyl insertion into other aromatic compounds will lead to a large suppression of aromatic character as judged by magnetic criteria and whether this suppression will be manifest in other criteria of aromatic character. Qualitative correlation between the magnetic, thermodynamic, spectroscopic, and calculational criteria of aromatic character is usually observed, but the interrelationships are sufficiently vague that it is not clear to what extent the present demonstration of a low degree of aromatic character for 1, 2, and 3 by magnetic criteria should be reflected in other criteria. For example, in considering the relationship between a suggested nmr-based quantitative criterion for aromaticity and the thermodynamic criterion for aromaticity, it was shown that in a thermo-dynamic comparison of the stabilization energy of Nmethyl-2-pyridone with 2-methoxypyridine the latter was found to be favored by only about 6 kcal/mol, while the nmr criterion suggested a much greater difference.2425 This lack of agreement could reflect failure (24) P.