Synthesis, spectral and electrochemical properties of novel 1,5-diphenyl-3-spirobifluorenyl pyrazoline derivatives

A series of novel 1,5-diphenyl-3-spirobifluorenyl pyrazoline derivatives have been synthesized and characterized by 1H NMR, X-ray crystallography, UV-vis and fluorescence spectroscopy and mass spectrometry. Their maximum UV-vis absorption wavelengths were between 386 and 395 nm, and the fluorescence emission wavelengths were between 459 and 469 nm, which belongs to the typical blue light emission. All compounds exhibited excellent absolute fluorescence quantum efficiency (AFQE) (>90%) in solution. Moreover, at solid phase, compound 4f also displayed good AFQE (54%). The energy gaps of these derivatives were between 2.8 and 3.0 eV, typical for the blue light emission. Molecular orbital calculations revealed that the HOMO and LUMO energy levels were close to 1,3-diphenyl-5-(9-phenanthryl)-4,5-dihydro-1H-pyrazole (DPPhP). The high fluorescence quantum efficiency, appropriate energy gaps and HOMO and LUMO energy levels prove that 1,5-diphenyl- 3-spirobifluorenyl pyrazoline derivatives have the potential to be used as blue light emitting materials.