Synthesis, photoluminescence and electrochemical properties of 2,7-diarylfluorene derivatives

A new class of highly fluorescent 9,9'-bis-(alkyl)-2,7-diarylfluorene having electron withdrawing or electron donating groups on the p-phenyl positions were synthesized and characterized. The highly luminescent fluorene derivatives, 1-6 showed blue emission (376-416 nm), narrow FWHM (similar to 50 nm), high quantum yield (phi(F) = 0.12-0.87) and short fluorescence lifetimes, tau(F) = 0.23-1.14 ns. The HOMO levels of 9,9'-bis-(alkyl)-fluorene were tuned by the p-substituents at 2,7-phenyl group. Hammett correlation with E-HOMO of these new molecules provides an effective tool to predict the HOMO level of similar molecules prior to the synthesis. These data indicate that they are useful as emitting materials for organic light emitting devices, OLEDs.