The regioselectivity and synthetic mechanism of 1,2-benzimidazole squaraines: combined experimental and theoretical studies

In this paper, a synthetic method to produce 1,2-benzimidazole squaraines with a yield of up to 89% is developed. It is found that both strong organic and inorganic bases have a satisfactory catalytic activity for this reaction. Theoretical studies provide detailed explanations for the 1,2 versus 1,3 condensation regiochemistry of the squaraines. The experimental and theoretical studies agree well with each other, paving a practical way to efficiently synthesize 1,2-squaraines.