Tetraanionic Oligo-Dioxaborines: Strongly Absorbing Near-Infrared Dyes

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 pi-system passes through three 1,3,2-dioxaborine units and a number of tri- and dimethine pi-bridges between two end-groups. The obtained dyes exhibit near-infrared absorption and fluorescence, with molar absorption coefficients reaching as high as 564000 M-1 cm-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. Strongly absorbing NIR polymethines of tetraanionic nature bearing 1,3,2-dioxaborine rings and different electron-accepting end-groups were synthesized and characterized. Due to a highly symmetric electronic structure of tetraanionic chromophore, the obtained dyes possess exceptionally high molar absorption coefficients (exceeding half a million) and good fluorescence quantum yields (up to 0.13). image