Activatable fluorogenic compounds and uses thereof as near infrared probes

A fluorogenic compound comprising three acceptor-containing moieties and a donor-containing moiety arranged such that:

• (i) said three acceptor-containing moieties and said donor-containing moiety form a conjugated π-electron system devoid of resonating electrons, such that the compound is incapable of emitting NIR infrared light;
• and
• (ii) upon a chemical event, said donor-containing moiety rearranges so as to transfer π-electrons to one of said acceptor-containing moieties and, as a result, said acceptor-containing moiety becomes a donor-containing moiety to the other acceptor-containing moieties, to thereby enable emission of near infrared light,
• wherein each of said acceptor-containing moieties is independently selected from an ammonium form of an indolenine or an ammonium form of a pyridine,
• and wherein said donor containing moiety comprises an aryl substituted by at least one electron-donating group, and is such that upon said chemical event, it rearranges by undergoing a quinonemethidine-like rearrangement,
• said donor-containing moiety being independently linked to each of said three acceptor-containing moieties either directly or via a linking moiety, said linking moiety comprising a carbomethine-containing chain of at least one —CR′═CR″— moiety, wherein R′ and R″ are each independently hydrogen, alkyl or cycloalkyl, or, alternatively, R′ and R″ form together an aryl, and is such that said acceptor-containing moieties and said donor containing moiety form said conjugated π-electron system.