Bipolar luminescent materials containing pyrimidine terminals: synthesis, photophysical properties and a theoretical study

Abstract

A new series of 4-monosubstituted pyrimidine bipolar materials containing a carbazole (PM1–PM2) or a triphenylamine (PM3–PM5) moiety as the electron donor have been synthesized by a ZnCl₂-catalyzed three-component coupling reaction. These 4-monosubstituted pyrimidine compounds were characterized by UV-vis and fluorescence spectroscopy, cyclic voltammetry, as well as density functional theory (DFT) calculations. It was intriguing to find that these 4-monosubstituted pyrimidine compounds exhibited bright fluorescence with excellent quantum yields (∼0.53–0.93) in the blue region. PM1 and PM2 had a lower LUMO than that of CBP (4,4′-di(9H-carbazol-9-yl)biphenyl), meaning that both of them had better electron injection and transfer abilities. The variation tendencies of energy levels and absorption spectra obtained from DFT calculations agreed well with those from experiment. Other electronic properties including ionization potentials (IP), electronic affinities (EA), and reorganization energies (λ_hole and λ_electron) have been theoretically studied as well. These electronic properties could be tuned by introducing a different number of pyrimdin-4-yl moieties onto to the donor fragments. The incorporation of pyrimdin-4-yl can significantly decrease the λ_electron and then improve the electron-accepting and hole–electron charge balance abilities. The combined theoretical and experimental studies offer insights into the nature of bipolar molecules containing 4-monosubstituted pyrimidine moieties, and provided a fertile ground for the design of appropriate ambipolar materials for optoelectronic applications.