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

Abstract

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 (1H, 13C, and 11B), FT-IR, and atmospheric pressure ionization time-of-flight mass spectrometry. BOSCHIBA1a 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.