Near-infrared squarate and croconate dianions derived from tetranitrofluorene

Squarylium and croconium dianionic dyes with tetranitrofluorene terminal groups have been synthesized. A distinctive feature of their absorption is multiple fairly intense bands in the VIS and NIR regions (up to 1060 nm). DFT quantum chemical calculation (including polarizing continuum simulation of solvent) was used to interpret their optical behaviour.