Asymmetrically twisted phenanthrimidazole derivatives as host materials for blue fluorescent, green and red...

The electroluminescent properties of asymmetrically twisted phenanthrimidazole derivatives comprised of fluorescent anthracene or pyrene unit namely, 1-(1-(anthracen-10-yl)naphthalen-4-yl)-2-styryl-1H-phenanthro[9,10-d]imidazole (ANSPI), 1-(1-(pyren-1-yl) naphthalene-4-yl)-2-styryl-1H-phenanthro[9,10-d]imidazole (PNSPI), 4-(2-(4-(anthracen-9-yl) styryl)-1H-phenanthro[9,10-d]imidazol-1-yl)naphthalene-1-carbonitrile (ASPINC) and 4-(2-(4-(pyren-1-yl)styryl)-1H-phenanthro[9,10-d]imidazol-1-yl)naphthalene-1-carbonitrile (PSPINC) for blue OLEDs have been analyzed. The asymmetrically twisted conformation interrupt π-conjugation effectively results in deep-blue emission. The pyrene containing PSPINC based non-doped blue device (476 nm) shows maximium efficiencies (current efficiency (η_c)-4.23 cd/A; power efficiency (η_p)-2.86 lm/W; external quantum efficiency (η_ex)-3.48%: CIE (0.16, 0.17) at 3.10 V. Among the doped blue devices, An(PPI)₂:ASPINC shows high efficiencies (η_c-12.13 cd/A; η_p-5.98 lm/W; η_ex-6.79%; L-23986 cd m^-2; EL-458 nm) at 3.15 V with CIE (0.15, 0.17) than An(PPI)₂:PSPINC based device which is inconsistent with non-doped device performances. The green and red PhOLEDs show higher efficiencies with Ir(ppy)₃: ASPINC (η_c-50.6 cd/A; η_p-53.4 lm/W; η_ex-17.0%; L-61581 cd m^-2; EL-501 nm, CIE (0.31, 0.60) at 3.32 V and (bt)₂Ir(dipba): ASPINC (η_c-15.2 cd/A; η_p-16.5 lm/W; η_ex-14.5%; L-13456 cd m^-2; EL-610 nm), CIE (0.63, 0.36) at 3.20 V, respectively. The complete energy transfer between the host and dopant molecules improved the efficiency of PHOLEDs.