Abstract
Metal tetrapyrrole macrocycles such as porphyrins and chlorins are ubiquitous in nature. Synthetic analogs, including phthalocyanines, have found applications in medicine, particularly as photosensitizers for photodynamic therapy and as fluorescent imaging probes. Tripyrrolic macrocycles, called subphthalocyanines (SPcs) with a smaller boron atom at their core, have similar potential as optical agents. We have recently reported a series of mixed fluorinated SPcs with varying aromaticity, showing that electronic absorption and emission are synthetically tunable across the far visible region, and that the inclusion of 4–12 peripheral fluorine atoms results in strong fluorescence within MDA-MB-231 breast tumor cells. Further probing this system, we report herein the synthesis and characterization of boron trifluorosubphthalocyanine chloride (F3SPc). The constitutional isomers F3SPc(C3) and F3SPc(C1) are readily separable by chromatography, and their identity and purity have been confirmed by 1H NMR, 19F NMR, HR APCI-MS, and HPLC. Unsurprisingly, these structurally similar F3SPcs have identical electronic absorption (λmax = 557 nm; tetrahydrofuran (THF)) and emission (λem = 574 nm; Φf = 0.27–0.28; THF). Strong fluorescence from MDA-MB-231 breast tumor cells was observed following treatment with F3SPc(C3) and F3SPc(C1) (50 µM F3SPc, 15 min), further highlighting the importance of even a limited number of peripheral fluorine atoms for this type of application.
Highlights
Subphthalocyanines (SPcs), contracted tripyrrolic cousins of tetrapyrrole phthalocyanines (Pcs), were first prepared in 1972 as a templated cyclization of phthalonitrile derivatives around a central boron atom [1]
Beryllium subphthalocyanines have emerged as promising molecules [4]; toxicity issues have far precluded the widespread attention that boron subphthalocyanines have garnered
Relevant to this communication, halogenated SPcs have been used in photovoltaic and organic light–emitting diode technologies [5,6,7,8], and other SPcs have been applied in biological systems as anti-cancer agents [9], optical imaging agents [10], and as antibacterial agents [11]
Summary
Subphthalocyanines (SPcs), contracted tripyrrolic cousins of tetrapyrrole phthalocyanines (Pcs), were first prepared in 1972 as a templated cyclization of phthalonitrile derivatives around a central boron atom [1]. We intend to build upon these limited biological studies by creating a library of fluorinated SPcs for application as either photodynamic therapeutics or fluorescent probes. These studies showed that electronic absorption and emission profiles are highly tunable visible region through variation of peripheral F-atoms and aromaticity. Other pyrrolic fluorescence to enhanced cellular uptake, presumably due to the F-atoms’ modulation of polarity or macrocycles with peripheral C–F bonds are known to undergo SN Ar reactivity, thereby replacing lipophilicity. Despite the the similar similar structure structure of literature where they can be separated chromatographically [25], and enantiomers can be further literature where they can be separated chromatographically [25], and enantiomers can be further resolved resolvedby bychiral chiralHPLC Owingto totheir their nearly nearly identical identical photophysical photophysical properties, properties, constitutional many practical applications as a mixture.
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