Star- and banana-shaped oligomers with a pyrimidine core:: Synthesis and light-emitting properties

By using Suzuki-Miyaura cross-coupling reactions we have synthesised a series of star- and banana-shaped oligomers with a pyrimidine unit as the central core and pi-conjugated arms consisting of aromatics bearing electron-donor substituents. The position of the arms as well as the nature of their substituents were investigated with a view to accessing compounds that exhibit interesting light-emitting properties. The best fluorescence quantum yields were obtained with banana-shaped pyrimidines substituted with p-(dimethyl-amino)phenyl or 2-furyl groups. Comparison of the optical properties of oligomers with benzene, pyrimidine or s-triazine as the central unit revealed that the pyrimidinic compounds gave the best results. Some of the oligomers synthesised exhibit solvatochromic properties and pH sensibility, which could allow their use as polarity or pH sensors. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008).