General procedure for the synthesis of 3,6-diiodo-9H-carbazole from carbazole: Carbazole (24 g, 144 mmol) was dissolved in acetic acid (360 mL) and heated to 80 °C. Subsequently, finely ground potassium iodide (31.5 g, 189 mmol) was added to the reaction system and stirred for several minutes. Next, potassium iodate (24 g, 100 mmol) was carefully added in portions and the reaction temperature was maintained at 80 °C until the iodine was completely consumed. After completion of the reaction, the mixture was cooled to 40 °C and the solid product was collected by filtration. It was washed sequentially with acetic acid (30 mL), methanol (100 mL) and water to afford 3,6-diiodo-9H-carbazole (51 g, 90% yield) as a yellow solid. NMR hydrogen spectrum (300MHz, CDCl3, δ): 8.33 (multiple peaks, 2H), 8.15 (multiple peaks, 1H), 7.70-7.60 (multiple peaks, 2H), 7.23-7.20 (multiple peaks, 2H).
