Synthesis and properties of furan/thiophene substituted difluoroboron β-diketonate derivatives bearing a triphenylamine moiety

Two novel triphenylamine-modified difluoroboron β-diketonate derivatives containing either a furan or thiophene unit (2c and 2d) have been designed, synthesized and fully characterized. The effects of the triphenylamine substituent and different electron-rich heterocycle units (2-furyl and 2-thienyl) on the photoluminescence and electrochemical properties of these new BF2 complexes were investigated systematically. The two complexes bearing an electron-donating triphenylamine moiety showed broad absorption and intense emission bands in toluene with high fluorescence quantum yields. Significantly larger Stokes shifts were observed for these complexes in comparison to those of the corresponding reference complexes (2a and 2b). Cyclic voltammetry measurements revealed the amphoteric redox properties of the two new BF2 complexes. The results indicated that the introduction of a triphenylamine substituent into BF2 complex could result in large differences in their properties. However, making a contrast between 2c and 2d, it is found that replacing furan with thiophene in the BF2 complex showed slight effects on optical and electrochemical properties. The results of DFT calculations supported the structural and spectroscopic data and confirmed the compositions of frontier molecular orbitals in the BF2 complexes.