9-(4-(3-Azidopyridin-4-yl)phenyl)-9H-carbazole (0.20 g, 0.553 mmol, 1.00 equiv.) was dissolved in acetonitrile (10 mL), and methyl iodide (0.118 g, 0.830 mmol, 1.50 equiv.) was added dropwise at room temperature with stirring. The resulting reaction mixture was left overnight at 40 °C. The precipitation was collected by filtration and washed with acetonitrile. After dissolving in 10 mL water, (0.451 g, 2.77 mmol, 5.00 equiv.) ammonium hexafluorophosphate was added, which resulted in a precipitate. The precipitate was collected by filtration and washed with water, and dried. After dissolving the solid in 10 mL of acetonitrile, (0.769 g, 2.77 mmol, 5.00 equiv.) tetrabutylammonium chloride was added, which resulted in a precipitate. The precipitate was collected by filtration and washed with acetonitrile, and dried. The desired product 4-(4-(9H-carbazol-9-yl)phenyl)-3-azido-1-methylpyridin-1-ium chloride was obtained as a pale yellow solid (0.192 g, 0.466 mmol, 84%).
