The fabrication strategies of near-infrared absorbing transition metal complexes

The fluorophores with absorption and emission in the near-infrared region have attracted increased attention and are widely used for bioimaging and phototherapy with high penetration depth, and signal-noise-ratio. Low spin d electronic configuration transition metal complexes have always displayed beneficial chemical and photophysical capabilities. Whereas, the majority of transition metal complexes are required short-wavelength and high-energy light to activate. Fabricating near-infrared absorbing transition metal complexes is therefore particularly meaningful through combining fluorophores with transition metal complexes or other ways. In this review, a brief introduction of near-infrared absorbing fluorophores is described. The design strategies of transition metal complexes absorbing near-infrared light are then overviewed and highlighted. The challenges and opportunities have been prospected in the meantime.