Cation-responsive turn-on fluorescence and absence of heavy atom effects of pyridyl-substituted triarylmethyl radicals

Pyridyl-substituted triarylmethyl radicals exhibited cation-responsive turn-on fluorescence when additional pyridyl rings were incorporated at an appropriate position; the mechanism of fluorescence enhancement is examined. Reduced quenching by internal and external heavy atom effects is proposed as a unique property of fluorescent radicals, which can be utilized in different environments to conventional closed-shell fluorescent molecules.