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Among the many experimentally observed tradeoffs between molecular hyperpolarizabilities and other useful properties is that between nonlinearity and thermal stability. Compounds with appreciable values of the first hyperpolarizability ß will be required if organic nonlinear optical materials are to find practical application in electrooptic devices or frequency doublers. 1 Such chromophores must alsobe sufficiently thermally robust to survive the fabrication steps for those devices. Additional thermal stability can be added to a nonlinear chromophore by substitution of aromatic moieties for aliphatic ones along the delocalized path between an electron donor and an acceptor; but since the hyperpolarizability is a measure of the ease of excitationto a state in which substantial intramolecular electron transfer has taken place, additional aromatic rings disfavor that electron transfer (since it would require them to adopt …