Structurally tuned benzo[h]chromene derivative as Pb2+ selective 'turn-on' fluorescence sensor for living cell imaging

A benzo[h]chromene derivative, 2-amino-4-phenyl-4H-benzo[h]chromene-3-carbonitrile 1, has been utilized as 'Turn On' fluorescence chemosensor for the selective detection of Pb2+. The title compound 1 was synthesized in one step using a multicomponent condensation reaction (MCR), and characterized using various spectroscopic techniques. The selectivity was tested over a range of 17 different metal and non-metal ions. Compound 1 was found to be weak fluorescent (Φ1=0.06) because of photoinduced electron transfer (PET). The presence of 2 equiv of Pb2+ showed a significant increase in fluorescence quantum yield (Φ1−Pb2+=0.132). A change in weak blue emission of 1 to a glowing green emission along with a prominent red shift (26 nm) in emission band was observed upon addition of Pb2+ to a methanolic solution of 1. The complexation of 1 with Pb2+ was proved by mass spectroscopy and NMR studies. Some of our experimental findings have been supported by theoretical studies. Compound 1 was found to be easily permeable to living cells without causing any harm and ultimately was used to detect effectively Pb2+ in living system.