Microwave-assisted solvent-free synthesis and luminescence properties of 2-substituted-4,5-di(2-furyl)-1<Emphasis Type="Italic">H</Emphasis>-imidazoles

A solvent-free microwave-assisted method for the synthesis of 2-substituted-4,5-di(2-furyl)-1H-imidazoles was developed. Imidazoles with moderate to good yields were produced by condensation of furil with aldehydes over acidic alumina impregnated with ammonium acetate, and they were characterized by FT-IR, HRMS, ¹H NMR and ¹³C NMR spectroscopy. Crystal structure of 2,4,5-tri-2-furyl-1H-imidazole (I) in the orthorhombic space group Pbca was reported, which showed more coplanarity than the reported crystal structure of I in the monoclinic space group Cc. Moreover, their luminescent properties were investigated. It was found that the organic small molecule compounds synthesized possess higher fluorescence quantum efficiency (up to 0.508) in a 0.1 M H₂SO₄ aqueous solution dissolved in 0.5 mL of CH₃OH; along with higher stability; also the emission of some compounds synthesized in the solution was sensitive to the polarity of the solvents.