Low-Symmetry Mixed Fluorinated Subphthalocyanines as Fluorescence Imaging Probes in MDA-MB-231 Breast Tumor Cells

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.

Synthesis of the C3 and C1 Constitutional Isomers of Trifluorosubphthalocyanine and Their Fluorescence within MDA-MB-231 Breast Tumor Cells

“…Analogous to other pyrrolic macrocycles [28], SPcs have two major absorption features, the Soret band (2nd HOMO → LUMO; λ max < 350 nm) and the Q-band (HOMO → LUMO; λ max > 500 nm). The F 3 SPc(C 3 ) and F 3 SPc(C 1 ) exhibit identical Q-band absorptions at 557 nm, representing a ~15 nm hypsochromic shift from previously reported perfluorinated SPcs (Figure 3, black) [20]. Upon excitation into the Soret band (λ ex = 325 nm), intense orange fluorescence is observed (λ em = 575 nm) (Figure 3, upper, red).…”

“…Breakage of the symmetry in F 3 SPc(C 1 ) results in three separate signals at δ −106.6, −106.7, and −106.9 ppm. These β–F signals lie ~30 ppm downfield from those of SPcs with F-atoms in both α and β positions [20], in line with the trend that the extent of fluorination alters 19 F chemical shifts further upfield.…”

“…We have recently studied a series of mixed fluorinated SPcs and subnapthalocyanines (SnPcs), made through co-cyclization of tetrafluorophthalonitrile, and phthalonitrile (SPcs) or 2,3-napthalenedicarbonitrile (SnPcs) [20]. These two reactions resulted in a series of macrocycles with a variable number of peripheral fluorine atoms (#F = 0, 4, 8, 12) and varied aromaticity (π e − = 14, 16, 18, 20).…”

Electronic Structure, Bonding, and Stability of Boron Subphthalocyanine Halides and Pseudohalides

“…In parallel with this basic progress, BsubPcs have been shown to possess many desirable properties for multiple applications. They can be easily applied as dyes and pigments [26][27][28][29][30] but can also be applied as fluorescence sensors, [31][32][33] optical imaging materials, [34] and photodynamic therapy sensors. [35] Particularly for their optical properties, but also for their tunable chemical Stick and space filling model representation of Cl-BsubPc in a solid-state arrangement, available through the CCDC database as PHTLBC02-1052234.…”

“…In parallel with this basic progress, BsubPcs have been shown to possess many desirable properties for multiple applications. They can be easily applied as dyes and pigments [ 26–30 ] but can also be applied as fluorescence sensors, [ 31–33 ] optical imaging materials, [ 34 ] and photodynamic therapy sensors. [ 35 ] Particularly for their optical properties, but also for their tunable chemical and thermal stabilities, low sublimation temperatures, and in some cases bipolar electrochemistry, BsubPcs have emerged as interesting semiconductors for organic photovoltaics (OPV) applications.…”