4,7,-ylstyry 1)-7-(dimethylamino)-1,4-benzoxazin-2-one undergoes drastic changes in emissive properties upon complexation by alkaline-earth cations, i.e. hypsochromic shift of the fluorescence spectrum and enhancement of quantum yield and lifetime. Comparison with the "uncrowned" molecule and with the reference compound in which the aza crown has been replaced by a dimethylamino group shows that the sensitivity to cation binding is closely related to the ability of the cation to hinder the electronic effects of the nitrogen atom of the crown. The values of the radiative and nonradiative rate constants reveal the role played by the dissipation of excitation energy due to rotation of the crown. The stability constants of the complexes with alkaline and alkaline-earth cations have been determined by fluorometric titrations; the values of these constants parallel the changes in photophysical properties.

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The synthesis of the 7‐dimethylamino‐1,4‐benzoxazin‐2‐ones (5), fluorescent dyes, by condensing α‐keto‐acids with 2‐amino‐5‐dimethylaminophenol is described. When the 3‐substituent is a methyl group, these compounds can be further condensed with aromatic aldehydes to provide the styryl dyes (6). These products are easily opened by hydrochloric acid in ethanolic solution to afford the corresponding benzalketoacid ethyl esters (7).

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