Abstract
Boron subphthalocyanines (SPcs) are aromatic macrocycles that possess a combination of physical and optical properties that make them excellent candidates for application as fluorescent imaging probes. These molecules have intense electronic absorption and emission, and structural versatility that allows for specific tuning of physical properties. Herein, we report the synthesis of a series of low-symmetry fluorinated SPcs and compare them to analogous compounds with varying numbers of peripheral fluorine atoms and varied aromaticity. Across the series, with increasing addition of fluorine atoms to the periphery of the ring, a downfield chemical shift in 19F NMR and a bathochromic shift of electronic absorption were observed. Expanding the size of the aromatic ring by replacing peripheral benzo- groups with naphtho- groups prompted a far more drastic bathochromic shift to absorption and emission. Fluorescence quantum yields (Φf) proved to be sufficiently high to observe intracellular fluorescence from MDA-MB-231 breast tumor cells in vitro by epifluorescence microscopy; fluorination proved vital for this purpose to improve solubility. This report lays the groundwork for the future development of these promising SPcs for their ultimate application as near-infrared (NIR) fluorescent imaging probes in biological systems.
Highlights
Boron subphthalocyanines (SPcs) are 14π-electron tripyrrolic macrocycles that were first discovered in 1972 [1], and have garnered significant attention for their structural versatility and optical properties, which has recently been reviewed extensively [2,3]
The ring system is conical in shape with an apical central boron with an axial ligand, usually a halogen (X = F, Cl, Br) [4], making these macrocycles more polar and less aggregative than their planar tetrapyrrole phthalocyanine (Pc) cousins
Like Pcs, SPcs are synthesized by the templated cyclization of phthalonitrile derivatives
Summary
Boron subphthalocyanines (SPcs) are 14π-electron tripyrrolic macrocycles that were first discovered in 1972 [1], and have garnered significant attention for their structural versatility and optical properties, which has recently been reviewed extensively [2,3]. Each SPc contains two types of fluorine atoms, α-F (non-peripheral) and β-F (peripheral), relative to the central pyrroles. Based on 19F NMR trends observed for various substituted fluorobenzenes [28], and analogous 1H NMR data for SPcs [2], we assign the non-peripheral F-atoms to be further upfield (more negative ppm) than peripheral F-atoms (Table 1). The naphtho- functionalized “AC” SPcs are more shielded than the analogous benzo- “AB” SPcs with the furthest upfield signal being for SPc(AC2). These data confirm identity of the fluorinated SPcs studied here, and provide a library of 19F chemical shifts for SPcs to be used in future synthetic refinement.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
