Synthesis and optical properties of phenanthromidazole derivatives for organic electroluminescent devices

Abstract

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 Alq₃-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 Alq₃ [tris(8-hydroxyquinoline)aluminium] layers. Using the device of ITO/NPB/4/Alq₃/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.