Near-infrared fluorescent probe based on rhodamine derivative for detection of NADH in live cells

A near-infrared fluorescent probe was prepared for selective detection of reduced nicotinamide adenine dinucleotide (NADH) in live cells. The probe turns off the fluorescence with a closed spironolactone switch. However, reduction of the probe by NADH turns on fluorescence at 740 nm. Theoretical calculations suggest a more planar arrangement between the rhodamine and quinoline moieties with increased π-delocalization resulting from reduction.