Developing strong NIR absorption materials through linear planar π-conjugated cyclopalladated complex dimers

Near-infrared absorption metal complexes (NIRMCs) have been traditionally associated with the pi-expanded macrocycle structure. However, macrocyclic ligands suitable for NIRMCs require a laborious synthetic route, and are a limited few. Herein, we report a kind of NIRMC based on linear large planar pi-conjugated cyclopalladated dimers, which can be obtained by a facile base-induced dimerization of corresponding monomers. These dimers show an intense absorption in the NIR region with epsilon(770 nm) = 2.5 x 10(5) cm(-1) M-1, and display a fluorescence emission peak at ca. 910 nm. Quinoid thiophene methine (QTM) and the cyclopalladated structure are speculated to be the key factors for their strong NIR absorption, which provides a different perspective of preparing NIR absorption metal complexes.

Automated summary

Linear large planar pi-conjugated cyclopalladated dimers obtained through a facile base-induced dimerization show strong NIR absorption and a fluorescence emission peak at around 910 nm. The key factors for their strong NIR absorption are speculated to be quinoid thiophene methine (QTM) and the cyclopalladated structure.