Yellow and blue make green: The importance of stoichiometry in the reaction of 1,4-bis(2,6-diisopropylphenyl)-1,4-diazabutadiene with dimethylgallium chloride

An unprecedented class of multichromic single crystals has been investigated after their initial discovery almost 15 years ago in industry. Single crystals have been prepared that are crystallographically identical, yet may be grown colorless, yellow, or green from crystal to crystal, or surprisingly, multicolored within the same crystal at all viewing angles, where one would expect that only a single color would exist. The system examined consisted of Me2GaCl complexed with 1,4-bis(2,6-diisopropylphenyl)-1,4-diazabutadiene in varying ratios. The work described is primarily geared towards understanding the factors leading to the multichromic nature of the complexes. Our results indicate that the most plausible explanation for the yellow/green mixed crystals is that the yellow crystals are contaminated with small amounts of an intensely-colored blue byproduct. In crystal regions where both the yellow and blue compounds are found, the crystals appear dark green. Identification of the blue byproduct was confirmed by X-ray diffraction.