Two new β-diketone-boron difluoride based near-infrared fluorescent probes 1 and 2 which exhibit polarity sensitivity have been designed and synthesized. Probes 1 and 2 are composed of a β-diketone-boron difluoride moiety as an acceptor unit, and a diethylamino group and a phenolic hydroxyl group as donor units. The long conjugate structures form a “donor–acceptor–donor” configuration, induce intramolecular charge transfer (ICT), and confer near-infrared fluorescence emission and excellent polarity sensitivity. The photophysical properties of these two probes were investigated in detail. Experimental data demonstrated that as the environmental polarity decreased, the fluorescence intensity of the probes increased obviously, accompanied by a blue-shift of the maximum emission wavelength. In addition, these two probes were photostable and solely sensitive to polarity without interference from viscosity, pH and common active species. Theoretical calculations indicated that probes 1 and 2 displayed lower energy gaps and faster non-radiative decay in polar solvents. Furthermore, probes 1 and 2 were utilized to quantitatively detect the polarity of a binary mixture through the satisfactory linear relationship between the fluorescence emission intensity ratios and the orientation polarizability of the mixed solvent. Additionally, probe 1 was successfully utilized to visualize the polarity distribution of live cells. Both of these probes are perfect candidates for studying polarity in vitro and even in live systems.

中文翻译：

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基于β-二酮-二氟化硼的新型近红外荧光探针用于极性检测

设计并合成了两种新的基于 β-二酮-二氟化硼的近红外荧光探针1和2，它们具有极性敏感性。探头1和2由作为受体单元的β-二酮-二氟化硼部分和作为供体单元的二乙氨基和酚羟基组成。长共轭结构形成“供体-受体-供体”构型，诱导分子内电荷转移 (ICT)，并赋予近红外荧光发射和优异的极性灵敏度。详细研究了这两种探针的光物理性质。实验数据表明，随着环境极性的降低，探针的荧光强度明显增加，同时最大发射波长发生蓝移。此外，这两种探针是光稳定的，仅对极性敏感，不受粘度、pH 值和常见活性物质的干扰。理论计算表明，探针1和2在极性溶剂中显示出更低的能隙和更快的非辐射衰减。此外，探针1和探针2用于通过荧光发射强度比与混合溶剂的取向极化率之间令人满意的线性关系来定量检测二元混合物的极性。此外，探针1已成功用于可视化活细胞的极性分布。这两种探针都是体外甚至在活系统中研究极性的完美候选者。