Fluorescent Modular Boron Systems Based on NNN- and ONO-Tridentate Ligands: Self-Assembly and Cell Imaging

Abstract

We have synthesized a series of new fluorescent boron systems 1a-c and 2a-d based on nitrogen (NNN) or nitrogen and oxygen (ONO)-containing tridentate ligands. These novel dyes are characterized by high thermal and chemical stability. They show large Stokes shifts (mostly above 3200 cm(-1)) and quantum yields in solution and in the solid state up to 40%. The easy, modular synthesis facilitates the convenient variation of the axial substituent on the central boron atom, allowing the functionalization of this dye for biochemical use. Introducing a long alkyl chain with a phenyl spacer at this axial position enables the self-assembly of the boron compound 2d to form a fluorescent vesicle, which is able to encapsulate small molecules such as sulforhodamine. Additionally, boron compound 2d was found to serve as a dye for cell imaging since it has the capability of binding to the nuclear membranes of HeLa cells. With phospholipids such as DOPC, giant unilamelar vesicles (GUV) are formed. These results demonstrate the wide applicability of this new boron system in supramolecular and medicinal chemistry.

Fluorescent benzene-centered mono-, bis- and tris-triazapentadiene–boron complexes

“…Therefore we decided to use the crude product 6e for further reactions since we know from experience that the triazapentadiene boron compounds are readily purified by either recrystallization or via column chromatography on alumina oxide. 15,21 Boron complexes 14a-e: the novel boron complexes derived from these ligands were synthesized by heating a solution of the respective triazapentadiene ligands 6a-e with 1 to 3 equivalents of triphenylborane in toluene under reflux for 5 hours (Scheme 4).…”

Facile synthesis of highly fluorescent BF2 complexes bearing isoindolin-1-one ligand

“…7 On the other hand, non-pyrrolic BODIPY analogues have recently attracted much interest and possess many advantages including the following: (1) readily available, cheaper and more stable starting materials; (2) easier synthesis, especially for the asymmetrical dyes and generally no oxidation step needed; (3) unparalleled diversity in structures; (4) larger Stokes shifts and better photostability of dyes. Thus, a variety of O,O-bi-, 8-10 N,N-bi-, 11,12 N,O-bi-, [13][14][15] O,N,O-tri-, 16,17 N,N,N-tri-, 17 and N,N,O,O-tetradentated 18 boron complexes have been efficiently synthesized and some show larger Stokes shifts with remarkable photostabilities.…”

“…So far, only limited BF 2 complexes of aza-BODIPY analogues have been reported. BF 2 complexes C and their π-extended boron complexes by Würthwein 17,19 and pyridine based dyes D, E and their derivatives by Fu, 20 and Zhu 21 all show high thermal, chemical stabilities and favorable photophysical properties. A class of BF 2 complexes F was recently synthesized by You and coworkers 22 through Pd catalyzed coupling reactions and showed mechanochromic luminescence.…”

Recent Advances in BODIPY Compounds: Synthetic Methods, Optical and Nonlinear Optical Properties, and Their Medical Applications

“…The results showed that the N→B coordinative bond facilitates the polarization of the electronic π-system, a situation that optimizes the third-order nonlinear optical (NLO) response. In addition, three boron complexes ( 65a – 65c ) were prepared by the reaction of bidentate ligands ( 66a – 66c ) and diphenylboronic acid ( Scheme 13 ) [ 69 ]. Compounds 58a and 58c were found to have a nonplanar conformation for the main p-backbone, acquired after boron complexation; for compound 58b , the planar conformation is preserved.…”