Synthesis, photophysical properties and systematic evaluations of new phenanthroimidazole fluorescent probe for bioimaging: Experimental and theoretical study

- For PB2 dye the charge-transfer excited state is more planar than the ground state.
- The PB2 compound exhibits the non-monotonic solvatochromism.
- The PB2 dye has potential applicability as a fluorescent probe.
- The PB2 conjugates with Concanavalin A in the active site near LYS200.

In this study, the newly synthesized 4′-(1H-phenantro[9,10-d]-imidazol-2-yl)-bifenyl-4-carboaldehyde - PB2 was investigated as a fluorescent dye. For this reason, the spectroscopic properties in solvents of different polarity were studied. The experimental data were supported by quantum-chemical calculations using density functional theory. Measurements and theoretical calculations showed that PB2 compound is characterized by the non-monotonic solvatochromism, strongly polar charge transfer excited state, large Stokes' shift, high fluorescence quantum yield and high fluorescence lifetime. Simulations using AutoDock presented in this study, showed that after conjugation with Concanavalin A in the active site with LYS200, the PB2 possesses the highest probability of binding affinity. Circular dichroism (CD) measurement was performed to monitor the changes of the secondary structure of Concanavalin A induced by the presence of PB2 fluorophore. These results indicate that the addition of PB2 influences the secondary structure of Concanavalin A, but does not affect the interactions with carbohydrate moieties. Finally, by using fluorescence microscopy it was demonstrated that the PB2 is the photostable fluorescent probe and PB2 conjugate Concanavalin A exhibits a blue fluorescence. The results of this study have implications in designing PB2-protein conjugate as a valuable alternative to commercial probes designed for cellular labeling in biological and biomedical research.

Graphical AbstractSpectroscopic properties of PB2-Concanavalin A conjugate.82