New furan fused 1,10-phenanthroline pentacyclic derivatives: Synthesis and photophysical properties

Two new donor-acceptor-donor (D-A-D) small molecules, named L1 and L2, based on furan-fused and fluorinated furan-fused 1,10-phenanthroline as electron-acceptor units and 4-(bis(4-methoxyphenyl)amino)phenyl as electron-donor units, were designed and synthesized. The photophysical and electrochemical properties were studied. The results are compared and discussed with respect to the influence of attached fluorine and solvent polarity. L1 and L2 emit intense blue light in non-polar solvent with high photoluminescence (PL) quantum yield (ηPL) of 1 for L2. The absorption and PL spectra of L2 with attached fluorine atoms are red-shifted compared with those of L1. Red shifts of PL maxima are observed with the increasing solvent polarity in solution spectra for both L1 and L2. ηPL values in solutions decrease as solvent polarity increases and the ηPL difference for L1 and L2 in solution is not so pronounced as for L1 and L2 thin films. In addition, the effect of protonation on the nitrogen atoms of phenanthroline in thin films is shown. L1 and L2 were tested in the light-emitting devices and their electroluminescent properties are also reported. The preliminary results show L1 and L2 are almost pure white emitter and greenish blue emitter, respectively.