Development of optical sensor for water in acetonitrile based on propeller-structured BODIPY-type pyridine-boron trifluoride complex.

A propeller-structured 3,5,8-trithienyl-BODIPY-type pyridine-boron trifluoride complex, ST-3-BF, which has three units of 2-(pyridin-4-yl)-3-(thiophen-2-yl)acrylonitrile at the 3-, 5-, and 8-positions on the BODIPY skeleton, was designed and developed as an intramolecular charge transfer (ICT)-type optical sensor for the detection of a trace amount of water in acetonitrile. The characterization of ST-3-BF was successfully determined by FTIR, H and B NMR measurements, high-resolution mass spectrometry (HRMS) analysis, thermogravimetry-differential thermal analysis (TG-DTA), photoabsorption and fluorescence spectral measurements, and density functional theory (DFT) calculations. ST-3-BF showed a broad photoabsorption band in the range of 600 to 800 nm, which is assigned to the S → S transition of the BODIPY skeleton with the expanded π-conjugated system over the 2-(pyridin-4-yl)-3-(thiophen-2-yl)acrylonitrile units at the 3-, 5-, and 8-positions onto the BODIPY core.