Into a 200-mL three-neck flask were put 1.2 g (4.5 mmol) of 2-chlorodibenzo[f,h]quinoxaline, 2.2 g (4.5 mmol) of 3,5-bis(dibenzothiophen-4-yl)phenylboronic acid, and 1.2 g (9.0 mmol) of potassium carbonate. To this mixture were added 23 mL of toluene, 4.5 mL of water, and 5 mL of ethanol, and this mixture was degassed by being stirred under reduced pressure. To the mixture was added 104 mg (0.09 mmol) of tetrakis(triphenylphosphine)palladium(0), and this mixture was stirred under a nitrogen stream at 100° C. for 3.5 hours. After the stirring, the obtained mixture was filtrated, and the solid was washed with water and then with ethanol. To the obtained solid was added toluene, and the mixture was suction-filtered through Celite, alumina, and Florisil. The filtrate was concentrated to give a solid. This solid was recrystallized from toluene, so that 1.4 g of a white solid was obtained in a yield of 46%. By a train sublimation method, 1.3 g of the obtained solid was purified. In the purification by sublimation, 2DBT2PDBq-II was heated at 320° C. under a pressure of 2.8 Pa with a flow rate of argon gas of 5 mL/min. After the purification by sublimation, 0.94 g of a white solid was obtained at a collection rate of 72%. The synthesis scheme of Step 3 is shown in (b-3).
