发展比率型近红外荧光探针对生物活性分子的识别、检测以及生物成像研究具有重要的意义。然而，能用于构建比率型近红外荧光探针，特别是能用于构建近红外荧光增强型的比率型荧光探针的近红外荧光染料分子非常缺乏。针对这一问题，本项目拟发展一系列结构新型的苯并吡喃共轭体作为新的近红外荧光染料分子，并研究这些共轭体分子在构建比率型近红外荧光探针中的应用。拟合成的探针分子不仅具有类似罗丹明分子可以通过“闭环-开环”机制来控制荧光“关-开”的特性，而且还可以做到比率型近红外荧光的变化。因此，本项目不仅为发展比率型近红外荧光探针提供了新的思路，而且通过项目的实施还有望发展一些性能优异的比率型近红外荧光探针，从而为生物活性分子的识别、检测和生物成像研究提供有效的分子工具。

The development of ratiometric and near-infrared (NIR) fluorescent probe is of great significance for the recognition, detection and bioimaging of biologically important molecules. However, the lack of appropriate NIR fluorescent dyes seriously hindered the development of such kind of probes, especially ratiometric probes with NIR fluorescent turn-on changes. In this proposal, benzopyrylium-based conjugates are proposed to be developed as new NIR fluorescent dyes for the development of ratiometric and NIR fluorescent probes. These conjugates not only contain a semi-rhodamine structure, which retained the unique merit of the “spirocyclization-spiroopening” mechanism of the widely-used rhodamine dyes for controlling their fluorescence, but also contain an additional fluorophore, which afford them new ideal platforms to construct ratiometric NIR fluorescent probes. Therefore, this project is expected to develop a series of benzopyrylium-based conjugates, and use them to develop some ratiometric NIR fluorescent probes with excellent sensing properties, thus providing useful molecular tools for the recognition, detection and bioimaging of biologically important molecules.