1-(4-Nitrophenyl)-benzimidazolium-based ratiometric chromogenic probes for cyanide ion

1,4- and 1,3-bis-[1-(4-nitrophenyl)-benzimidazolium-3-methylene]benzene derivatives 3b and 4b elaborate ratiometric chromogenic probes for the estimation of 1-270 μM cyanide ion.