Oxidized bis(indolyl)methane: a simple and efficient chromogenic-sensing molecule based on the proton transfer signaling mode.

[reaction: see text] Oxidized bis(indolyl)methane, 1, a simple chromophore containing an acidic H-bond donor moiety and a basic H-bond acceptor moiety, can act as a selective colorimetric sensor either for F(-) in aprotic solvent or for HSO(4)(-) and weak acidic species in water-containing medium. The deprotonation/protonation of oxidized bis(indolyl)methane 1 is responsible for the dramatic color change.