Functionalized coumarin derivatives containing aromatic-imidazole unit as organic luminescent materials

Three new coumarin derivatives containing aromatic-imidazole unit (i.e., benzo[d]imidazole, phenanthro[9,10-d]imidazole and pyreno[4,5-d]imidazole), 3-(1-phenyl-1H-benzo[d]imidazole-2-yl)-7-(diethylamino)coumarin (BI-C), 3-(1-(4-(tert-butyl)phenyl)-1H-phenanthro[9,10-d]imidazole-2-yl)-7-(diethylamino)coumarin (PI-C) and 3-(9-(4-(tert-butyl)phenyl)-9H-pyreno[4,5-d]imidazole-10-yl)-7-(diethylamino)coumarin (PyI-C), were successfully prepared for organic light-emitting devices. These compounds show good thermal properties and strong emissions from greenish-blue to green lights owing to the extended pi-conjugation of the rigid polyaromatic imidazole skeleton, and have high photoluminescence quantum efficiency of 94%, 97% and 98% in chloroform solutions. Among these compounds, the doped organic light-emitting device fabricated from the compound PI-C exhibited the maximum luminous efficiency of 6.07 cd/A and maximum EQE of 2.78%.