Synthesis, optical properties, and blue electroluminescence of fluorene derivatives containing multiple imidazoles bearing polyaromatic hydrocarbons

Fluorene decorated with multiple imidazole units in a non-conjugated fashion and featuring polyaromatic hydrocarbons such as anthracene or pyrene were synthesized and characterized as blue emitters suitable for application in organic light-emitting diodes. The optical absorption and emission peak profiles remained unaltered on increasing the imidazole loading on fluorene. But the molar extinction coefficient progressively increased on introduction of additional imidazole unit attributable to the increment in the chromophore density. Replacement of phenyl group at the C-2 of imidazole nucleus with polyaromatic hydrocarbons such as anthracene and pyrene led to a red-shift in the absorption and emission spectra due to their characteristic absorption features. All the compounds exhibited high thermal decomposition temperature in the range 395–509 °C showing significant thermal robustness. The anthracene and pyrene derivatives were demonstrated as efficient blue emitters in 4,4′-di(9H-carbazol-9-yl)-1,1′-biphenyl host for multilayered organic light-emitting diodes.