Studies of novel diazanaphthoquinones and ion-responsive fluorescent quinoxaline derivatives
The work reported is divided into two parts: fIrstly a section dealing with the preparation of some novel diazanaphthoquinones and their reactions, especially the Diels-Alder reaction, and secondly an account of some quinoxaline derivatives and their fluorescence properties. Quinoxaline quinones containing electron-donating groups at both the 2- and 3- position have shown a difference in their stability and their behaviour in the Diels-Alder reaction compared to the stability and the reactions of quinoxaline quinone. Symmetrical dienes in the Diels-Alder reaction yielded the initial addition products, which were resistant to oxidation, whereas unsymmetrical dienes produced fully aromatized products. Crown ether derivatives of 5,8-dimethoxyquinoxaline and the corresponding quinoxaline quinones were prepared. An improved method for the preparation of a fluorescent derivatising reagent is described. This compound was then used to prepare ion-responsive fluoroionophores containing monoazacrown ethers of different cavity sizes. The complexation of these fluoroionophores, in dichloromethane, was achieved by using perchlorates of alkali and alkaline earth metals. A strong correlation between the size of the metal ion and the cavity size of the crown ether was seen in the fluorescence quantum yields of the complex, and a fluoroionophore containing a diazacrown ether gave particularly noteworthy results. A bathochromic shift with a strong hyperchromic effect was the most important feature caused by complexation with metal ions for these fluoroionophores. Fluorescent open chain ethers (podands) were also prepared and their complexation with metal ions was studied. A strong bathochromic shift and a hypochromic effect was observed especially in their excitation spectra. A further novel fluorescent derivatising reagent was prepared by extending the conjugated system. This gave the expected improved results upon the preparation of the derivatives including fluoroionophores having crown ethers of different cavity sizes. However, the changes in fluorescence did not correlate with the relationship between the sizes of the metals ion and the cavity of the crown ether. Nevertheless, a large bathochromic shift was observed on complexation with metal ions.