Tetrathienyl-functionalized red- and NIR-absorbing BODIPY dyes appending various peripheral substituents

A series of boron-dipyrromethene dyes (BODIPYs) 4a-g with different thienyl moieties at 2,3,5,6-positions of the BODIPY core were synthesized by the Stille cross-coupling reaction. The new compounds were characterized by ¹H NMR, ¹³C NMR, HRMS, and IR spectroscopy. The single crystal structure of compound 4e was obtained by X-ray crystallography. The optical and electrochemical properties of these dyes were studied by UV/Vis spectroscopy, fluorescence spectroscopy, and cyclic voltammetry. The DFT calculation of the frontier molecular orbitals of these dyes corroborates the observed effects of peripheral substituents on the optical and redox properties. These results reveal a good tunability of the optical and electronic properties of these BODIPYs by varying the peripheral groups at the α-positions of thienyl moieties, which leads to the absorption and emission reaching the NIR region.