A cyclo-meta-phenylene (CMP) macrocycle with donor/acceptor substituents was designed. After optimization of the synthesis routes, the CMP congener was synthesized via [3 + 3] assembly of phenylene panels in moderate yield. The molecule showed a highly crystalline nature, and a single crystal formed upon sublimation. The molecule was transparent in the visible light region and was thermally robust with a decomposition temperature of 583 âą C. The effect of the donor/acceptor substituents was evaluated for charge carrier transport layers in emitter-doped phosphorescent OLEDs, which showed a dramatic improvement in its electron transporting ability as well as power efficiency in devices. Structural modification is one of the most intriguing potentials of organic materials. Integration of requisite characteristics via structural modification often holds a key role for the development of promising materials from a privileged core structure.1 Through our investigations on nanocarbon-inspired molecules, 2-4 we have casted a spotlight on arylene macrocycles as organic electronic materials.5-8 Thus, a series of macrocyclic hydrocarbons, in particular, [n]cyclo-meta-phenylenes (CMPs; Figure 1) 9 revealed unique potentials of their cyclic Ï-systems to be embedded in organic light-emitting devices (OLEDs).10,11 After revealing a bipolar charge carrier transport ability of the unsubstituted [n]CMP, 9 we introduced bulky substituents at the macrocyclic periphery to find multirole hydrocarbon materials for highly efficient single-layer OLEDs. 12,13 In this study, we envisioned the periphery modification for electronic tuning of OLED materials and designed a donor/acceptor conjugate of [6]CMP. Among two synthesis routes examined, a homo-coupling route via [3 + 3] assembly of phenylene panels was found superior to a [1 + 2 + 1 + 2] cross-coupling route. The electronic tuning with donor/acceptor substituents resulted in a highly crystalline nature of the CMP congener and in improvements of the performances in OLEDs.
Experimental
Synthesis of 3:A mixture of bis(1,5-cyclooctadiene)nickel(0) (2.48 g, 9.02 mmol), 2,2'-bipyridyl (1.41 g, 9.03 mmol), 1,5-cyclooctadiene (1.11 ml, 9.05 mmol), DMF (150 mL) and toluene (150 mL) was stirred at room temperature for 30 minutes. The precursor terphenyl 6 was stirred in toluene (601 mL) at 80âą C, and to this solution was added the solution of Ni complex. After 1 h, 1 M HCl (50 mL) was added, and the mixture was stirred for 3 h. Precipitates were removed by filtration, and the filtrate was extracted with toluene (500 mL Ă 3). Combined organic solution was dried over MgSO 4 to afford a crude material after removal of volatile materials. The crude material was washed with CHCl 3 (80 mL) and was recrystallized from nitrobenzene to give 3 in 20% yield (417 mg, 0.446 mmol). For the device application, the solid was further purified by sublimation.z E-mail: satosota@m.tohoku.ac.jp; isobe@m.tohoku.ac.jpOLEDs were fabricated and evaluated by using methods reported in previous studies. 4, 140.3, 140.2, ...