Abstract
Comparative optical, electroluminescence and theoretical studies were performed for (E)-4′-(1-(4-(2-(1-(4-morpholinophenyl)-1H-phenanthro[9,10-d]imidazol-2-yl)vinyl)phenyl)-1H-phenanthro[9,10-d]imidazol-2-yl)-N,N-diphenyl-[1,1′-biphenyl]-4-amine (SMPI-TPA) and (E)-4-(4-(2-(4-(2-(4-(9H-carbazol-9-yl)phenyl)-1H-phenanthro[9,10-d]imidazol-1-yl)styryl)-1H-phenanthro[9,10-d]imidazol-1-yl)phenyl)morpholine (SMPI-Cz). These compounds show excellent thermal properties, dual charge transport properties and form thin films under thermal evaporation. Blue OLEDs (CIE: 0.16, 0.08) based on SMPI-TPA show efficient device performance (ηex 6.1%; ηc 5.3 cd A−1; ηp 5.2 lm W−1) at low turn-on voltages. Both SMPI-TPA and SMPI-Cz were utilised as hosts for green OLEDs. The devices with SMPI-Cz (30 nm):5 wt% Ir(ppy)3 exhibit maximum luminance of 20 725 cd m−2, and ηc and ηp values of 61.4 cd A−1 and 63.8 lm W−1, respectively. In comparison, devices with SMPI-TPA (30 nm):5 wt% Ir(ppy)3 exhibit high ηc and ηp values of 65.2 cd A−1 and 67.1 lm W−1, respectively. Maximum ηex values of 19.6% and 23.4% were obtained from SMPI-TPA:Ir(ppy)3 and SMPI-Cz:Ir(ppy)3, respectively. These device performances indicate that the phenanthroimidazole unit is a tunable building unit for efficient carrier injection and it may also be employed as a host for green OLEDs.
Highlights
These device performances indicate that the phenanthroimidazole unit is a tunable building unit for efficient carrier injection and it may be employed as a host for green OLEDs
As depicted in Scheme S1,† the blue emitters used as hosts for green OLEDs, namely, (E)-40-(1-(4-(2-(1-(4-morpholinophenyl)1H-phenanthro[9,10-d]imidazol-2-yl)vinyl)phenyl)-1H-phenanthro[9,10-d]imidazol-2-yl)-N,N-diphenyl-[1,10-biphenyl]-4-amine (SMPI-TPA) and (E)-4-(4-(2-(4-(2-(4-(9H-carbazol-9-yl)phenyl)-1Hphenanthro[9,10-d] imidazol-1-yl)styryl)-1H-phenanthro[9,10-d] imidazol-1-yl)phenyl)morpholine (SMPI-Cz) were prepared from phenanthrenequinone (0.416 g, 2 mmol), 40(diphenylamino)biphenyl-4-carbaldehyde (SMPI-TPA)/4-(9Hcarbazol-9-yl)benzaldehyde (SMPI-Cz), 4-((E)-2-(1-(4-morpholinophenyl)-1H-phenanthro[9,10-d]imidazol-2-yl)vinyl)benzenamine and ammonium acetate in acetic acid (120 C; 12 h; N2 stream)
The potential energy surface diagrams (Fig. 1a and b) reveal that the minimum energy conformation corresponds to that in which the 4-morpholinophenyl ring attached to the imidazole nitrogen atom (N23) is tilted to an angle of 98.21 (SMPI-Cz)/ 101.1 (SMPI-TPA) and the phenyl ring with carbazole core (SMPI-Cz) and another phenyl ring with triphenylamine core (SMPI-TPA) are attached to the imidazole carbon atom (C25) at an angle of 91.56 (SMPI-Cz)/110.1 (SMPI-TPA) (Fig. 1c)
Summary
Efficient green or red OLEDs with pure color CIE coordinates have been reported[1,2,3,4] and blue emitters with less power consumption in organic optoelectronics have been broadly studied.[5,6] there is need for long-lifetime blue emitters with pure colour CIE coordinates due to wide band gaps (Eg), which require limited p-conjugation length.[7,8,9] Simultaneous carrier injection into a blue-emissive layer becomes very difficult due to its wide Eg, resulting in a decrease in device efficiency.[10,11] for OLED applications, highly efficient and low-cost blue OLEDs are of urgent demand. The. A blue-emissive material with high triplet energy (ET) may be employed as a host for green OLEDs.[13,14,15,16] the high triplet energy enables green emitters to harvest the triplet energy of a blue emitter; efficient non-doped blue emitters are not suitable as hosts for phosphorescent OLEDs due to their low ET as well as poor carrier transport properties.[17] efficient hosts for green emitter exhibit low efficiency when they are used as emissive materials in blue OLEDs.[18,19,20] efforts are still required to achieve efficient OLEDs based on blue emissive materials. To develop dual-functional emissive materials, i.e., emitters for blue OLEDs and hosts for green OLEDs, synthesis of molecules with donor (D)/acceptor (A) (electron/ hole transport moieties) con guration has gained interest. These derivatives exhibit higher stability with balanced injection property, leading to excellent device performances
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
