Synthesis and light-emitting properties of 2-(N-phenyl-α-naphthylamino) and 2-dimesitylboron-7-(N-phenyl-α-naphthylamino)-9,9-diethylfluorene

A fluorescent organic triarylamine with a symmetric structure, 2,7-bis(N-α-naphthyl-phenylamino)-9,9- diethylfluorene (NPAEF) was synthesized using two methods, modified Ullmann coupling and modified palladium-catalyzed amination. An activated copper and a combination of Pd(OAc)2/P(t-Bu)3 and Pd(dba)2/P(t-Bu)3 were selected as catalysts to improve yields of reactions. These synthetic procedures were also successfully applied to an asymmetric 2-dimesitylboron-7-(N-phenyl-α-naphthylamino)-9,9-diethylfluorene (BNPEF). Photoluminescent emission peaks in solid film and in diluted solution of NPAEF were both observed at 461 nm, while the main emission peaks of BNPEF appeared at 422 nm in hexane, and at 480 nm in methanol. The double emission peaks of BNPEF in hexane reflected fine structure in the vibrational state. With an increasing polarity of solvent, the main PL emission peaks were red-shifted and vibrational fine structure disappeared. Additionally, energy levels of NPAEF were investigated and an electroluminescence (EL) device of ITO/PVK:NPAEF/Al was fabricated, which showed a turn-on voltage of 9 V and peaked at 462 nm. The EL spectrum was in good agreement with PL spectrum, which indicated that they were from the same emitting center in the device.