Polymethine dyes of tetraanionic nature comprising 1,3,2-dioxaborine rings in the polymethine chain and end-groups of different electron-accepting abilities have been synthesized. They can be considered as oligomeric polymethines, where a linear conjugated π-system passes through three 1,3,2-dioxaborine units and a number of tri- and dimethine π-bridges between two end-groups. The obtained dyes exhibit near-infrared absorption and fluorescence, with molar absorption coefficients reaching as high as 564000 M−1cm−1 in DMF, rendering them among the strongest absorbers known. The novel compounds are bright NIR fluorophores, with fluorescence quantum yields up to 0.13 in DMF. A comparative analysis of the electronic structure of the obtained dyes with respective dianionic and trianionic oligomers was conducted through quantum chemical calculations.

中文翻译：

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四阴离子低聚二氧硼烷：强吸收近红外染料

合成了四阴离子性质的聚次甲基染料，其在聚次甲基链中包含1,3,2-二氧杂硼啉环和具有不同电子接受能力的端基。它们可以被视为低聚聚次甲基，其中线性共轭 π 系统穿过三个 1,3,2-二氧杂硼啉单元以及两个端基之间的多个三和二次甲基 π 桥。所得染料表现出近红外吸收和荧光，在DMF中摩尔吸收系数高达564000 M−1cm−1，使其成为已知最强的吸收剂之一。这些新型化合物是明亮的近红外荧光团，在 DMF 中的荧光量子产率高达 0.13。通过量子化学计算对所得染料与各自的双阴离子和三阴离子低聚物的电子结构进行了比较分析。