Synthesis, characterization, photophysical properties of new fluorescent boron Schiff bases (BOSCHIBAs) and their application as cytoplasm staining dyes in vitro

In this paper, we report a series of Schiff bases synthesized by the condensation reaction between 2-hydroxy-1-naphthaldehyde with aniline derivatives as well as their further coordination with diphenylborinic acid for giving the corresponding boron Schiff bases (BOSCHIBAs) ( E )-N-((2-((di-phenylboryl)oxy)naphthalen-1-yl)methylene)pyridin-3-amine ( 1a ), ( E )-N-((2-((di-phenylboryl)oxy)naphthalen-1-yl)methylene)-2,6-di-methylaniline ( 2a ), and ( E )-N-((2-((di-phenylboryl)oxy)naphthalen-1-yl)methylene)-2,6-di-isopropylaniline ( 3a ). The resulting BOSCHIBAs were characterized by NMR ( 1 H, 13 C, and 11 B), FT-IR, and atmospheric pressure ionization time-of-flight mass spectrometry. BOSCHIBA 1a was structurally characterized by single-crystal. Structure analysis indicates that the boron atom adopts a tetrahedral molecular geometry into a six-membered ring with a half-chair conformation. BOSCHIBAs 1a - 3a and their ligands 1 - 3 exhibit relatively low quantum yields in a range from 1 to 3%. In a bioimaging study by using the BOSCHIBAs 2a , and 3a as fluorescent staining dyes, those materials showed enhanced features in terms of low cytotoxicity, simple synthesis, photostability, hydrolytic stability and specific staining for cytoplasm structures.