The photophysics, crystal and electronic structures of some novel benzene-linked bisimidazole compounds

Several novel disubstituted benzene-bridged bisimidazole derivatives (3a-3h) were prepared and characterized. Their optical properties, crystal structures and quantum chemical calculations were also investigated. The UV-vis spectra observed (λ^Abs_max: 325-348 nm) in acetonitrile showed low optical band gaps (E_g^opt: 2.89-3.25 eV). All these compounds display strong fluorescence in solution with emission spectra (λ^Em_max: 389.5-418 nm) (fluorescence quantum yield in the range 0.46-0.95) and significant Stokes shift (3670-5490 cm^-1). The single crystal structures of 3h solvates were presented and discussed. The space groups of 3h solvates (3h1: 3h·2H ₂O and 3h2: 3h·DMSO·2H₂O) were C ₂/c and P2₁/c, respectively. Quantum chemical calculations using DFT B3LYP/6-31G(d) showed obvious difference in LUMO (-1.273 to -1.715 eV) and HOMO (-4.838 to -5.296 eV) while they were similar in E_g ^cal (3.393-3.599 eV) values of these compounds. These results demonstrate that these novel disubstituted benzene-bridged bisimidazole derivatives are promising electron-transporting electro luminescent materials and blue-light emitting materials for OLED.