Synthesis and optical properties of phenanthromidazole derivatives for organic electroluminescent devices

Five phenanthromidazole derivatives, namely 2-(naphthalen-1-yl)-1H-phenanthro[9,10-d]imidazole (1), 2-(naphthalen-1-yl)-1-phenyl-1H-phenanthro[9,10-d]imidazole (2), 2-(naphthalen-1-yl)-1-p-tolyl-1H-phenanthro[9,10-d]imidazole (3), 1-(4-methoxyphenyl)-2-(naphthalen-1-yl)-1H-phenanthro[9,10-d]imidazole (4) and 1-(3,5-dimethylphenyl)-2-(naphthalen-1-yl)-1H-phenanthro[9,10-d]imidazole (5), were synthesised using the TiO2 (R) nanosemiconductor as the catalyst under solvent free conditions and characterised by NMR and single crystal XRD techniques. Their photophysical, electrochemical and electroluminescent properties were carefully analysed. Highly efficient Alq(3)-based organic light emitting devices have been developed using phenanthromidazoles as functional layers between NPB [4,4-bis(N-(1-naphthyl)-N-phenylamino)biphenyl] and Alq(3) [tris(8-hydroxyquinoline)aluminium] layers. Using the device of ITO/NPB/4/Alq(3)/LiF/Al, a maximum luminous efficiency of 5.99 cd A(-1) was obtained with a maximum brightness of 40 623 cd m(-2) and a power efficiency of 5.25 lm W-1.