A Dimethylaminophenyl-Substituted Naphtho[1,2-b]quinolizinium as a Multicolor NIR Probe for the Fluorimetric Detection of Intracellular Nucleic Acids and Proteins

The dye 3-(4-(N,N-dimethylamino)phenyl)naphtho[1,2-b]quinolizinium was synthesized by means of a Suzuki–Miyaura reaction in good yield, and its binding properties with duplex DNA, quadruplex DNA (G4-DNA), RNA, and bovine serum albumin (BSA) were investigated by photometric, fluorimetric and polarimetric titrations and DNA denaturation analysis. The compound intercalates into DNA and RNA, associates in binding site I of BSA, and binds to G4-DNA by terminal π stacking. The ligand exhibits a fluorescence light-up effect upon complexation to these biomacromolecules, which is more pronounced and blue shifted in the presence of BSA (Φfl=0.29, λfl=627 nm) than with the nucleic acids (Φfl=0.01–0.05, λfl=725–750 nm). Furthermore, the triple-exponential fluorescence decay of the probe when bound to biomacromolecules in a cell enables their visualization in this medium and the differential labeling of cellular components.