Design and Synthesis of Near-Infrared Fluorescent Dyes of Difluoroboron β-Diketonate and Cell Imaging

doi:10.6023/cjoc202404032

Abstract

Near-infrared (NIR) luminescent materials have great potential in the field of bioimaging due to their unique advantages of strong tissue penetration and weak light scattering in biological tissues. In this study, a donor-acceptor (D-A) structured boron difluoride β-diketonate complex (TPA-BF₂-CN) was designed and synthesized through the strategy of enhancing intramolecular charge transfer. This complex exhibits solvent-dependent luminescent properties. It demonstrates good luminescence efficiency in dilute solution and solid state with efficiencies of 11.1% and 5.9%, respectively. The maximum emission wavelength peaks at 760 nm, falling within the NIR range. The complex also possesses mechanochromic properties with a redshift of emission wavelength by 107 nm after grinding. TPA-BF₂-CN exhibits dual emission fluorescence phenomenon with emission peaks located in the blue light region at 400 nm and the NIR region at 760 nm with an emission wavelength range of 690~850 nm in the NIR region. Compared to single-channel fluorescent molecules, it has the advantage of avoiding interference from environmental factors. Cell imaging studies demonstrate good compatibility of TPA-BF₂-CN with HeLa cells, and NIR emission signals can be observed throughout the cytoplasmic region of HeLa cells. Therefore, TPA-BF₂-CN can serve as a fluorescent probe for live cell imaging.

Key words: difluoroboron β-diketonate, near-infrared, cell imaging, mechanochromic, dual-state emission

Cite this article

Yunpeng Qi, Wei Liu, Junlong Wang, Tao Du, Songlin Jiao. Design and Synthesis of Near-Infrared Fluorescent Dyes of Difluoroboron β-Diketonate and Cell Imaging[J]. Chinese Journal of Organic Chemistry, 2024, 44(11): 3357-3364.

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Fig. & Tab. 10

Scheme 1. Synthetic route to the TPA-BF2-CN

In solution						Pristine powder				Ground powder
Solvent	λ_abs^a/nm	ε^b/(L•mol^－1•cm^－1)	λ_em^c/nm	Stokes shift	Φ_f^d/%	τ^e/ns	λ_em^f/nm	λ_em^g/nm	Φ_f^d	Φ_f^d/%	λ_em^f/nm	λ_em^g/nm
Hexane	471	8660	539	2678	10.0
Toluene	484	44310	598	3938	11.1
THF	485	32590	588	3611	5.1	3.09	627	396/760	5.9	0.2	695	397/698
DCM	494	58150	620	4113	2.3
DMSO	495	35640	603	3618	2.2

Table 1. Photophysical data of TPA-BF2-CN in various states

Figure 1. Normalized UV-vis spectra of TPA-BF2-CN in various solvents

Figure 2. Normalized fluorescence spectra of TPA-BF2-CN in various solvents (A), and photographs of TPA-BF2-CN in various solvents (B)

Figure 3. Molecular orbital amplitude plots of HOMO and LUMO levels for TPA-BF2-CN

Figure 4. Fluorescence emission spectra of TPA-BF2-CN in the THF/water mixtures with different fractions of water (A), and photographs in THF/water mixtures of TPA-BF2-CN under 365 nm UV illumination (B)

Figure 5. Fluorescence emission spectra of TPA-BF2-CN in glycerol solution at different temperatures Insert: trends of fluorescence intensity changes of TPA-BF2-CN in glycerol solution at different temperatures.

Figure 6. Fluorescence emission spectrum of solid TPA-BF2-CN under 490 nm excitation (A), fluorescence emission spectrum of solid TPA-BF2-CN under 320 nm excitation (B), XRD spectrum of TPA-BF2-CN in different solid states (C), and photographs of TPA-BF2-CN in different solid states under UV light (D)

Figure 7. Toxicity of TPA-BF2-CN to HeLa cells using the MTT assay

Figure 8. CLSM images of HeLa cells incubated with TPA-BF2- CN (A) Images in blue channel (λex=405 nm, λem=410~466 nm); (B) Images in red channel (λex=405 nm, λem=626~672 nm); (C) Images in green channel (λex=488 nm, λem=597~624 nm); (D) Images in bright field channel; (E) Overlay of A, B, C, D, and F; (F) Images in NIR channel (λex=488 nm, λem=626~663 nm).

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