Pyrrolopyrrole cyanine dyes: a new class of near-infrared dyes and fluorophores.

Pyrrolopyrrole cyanine (PPCy) dyes are presented as a novel class of near-infrared (NIR) chromophores, which are synthesized in a condensation reaction of diketopyrrolopyrrole with heteroarylacetonitrile compounds. Their optical properties are marked by strong and narrow-band NIR absorptions. Complexation products with BF(2) and BPh(2) show strong NIR fluorescence and hardly any absorption in the visible range. We synthesized a series of new PPCys that differ only in the heterocyclic peripheral groups of the chromophore. With this strategy, the absorption spectra can be tuned between 684 and 864 nm, while high fluorescence quantum yields are maintained. The influence of the heterocycle on the optical properties of the dyes is discussed.