Synthesis of (E)-5-(2-arylvinyl)-2-(hetero)arylpyridines, (E)-2-(2-arylvinyl)-5-methoxycarbonylpyridines and (E,E)-2,5-bis(2-arylvinyl)pyridines as polarity and pH probes

Abstract

In this report we describe the synthesis and photophysical properties of various (E)-5-(2-arylvinyl)-2-(hetero)arylpyridines 7a–f, (E)-2-(2-arylvinyl)-5-methoxycarbonylpyridines 14a,b and (E,E)-2,5-bis(2-arylvinyl)pyridines 13a,b. The fluorescence spectra and the fluorescence quantum yields of these versatile molecules depend strongly on the polarity and proton donor character of the environment. While the smaller excited state dipole moment of the (E)-2-(2-arylvinyl)-5-methoxycarbonylpyridines 14a,b leads to a smaller polarity dependence, the fluorescence of these molecules is characterized by a larger dependence on the proton donor character of the environment. On the other hand, the fluorescence maximum of the (E,E)-2,5-bis(2-arylvinyl)pyridines 13a,b shows an extremely large dependence on the solvent polarity, but, until salt formation occurs, the proton donor character of the environment hardly influences the fluorescence maximum. The combination of the complementary photophysical properties of both molecules and the synthetic accessibility of derivatives with a large variety of substituents, allowing selective incorporation in various environments, makes them an interesting class of probes.