Functional terpyridyl iron complexes for in vivo photoacoustic imaging

Photoacoustic (PA) imaging has received extensive attention in the recent decade due to its ultra-high resolution in deep tissue penetration, whereas functional PA probes with tunable molecular structure at a low cost level remain a significant challenge. Herein, we have rationally designed three triple-pyridyl iron complexes with different water solubilities. These complexes show a higher photothermal conversion efficiency due to their rapid excited-state deactivation, making them suitable as PA probes. Notably, the photothermal conversion efficiency of one complex named S-Fe could reach as high as 29.6%. In addition, S-Fe has excellent solubility and biocompatibility, which enable PA imaging in vivo. Significantly, further pharmacokinetics evaluation demonstrated that this complex showed minimal invasiveness for live animals and displayed a relatively fast metabolism rate. This study using inexpensive iron complexes as PA agents upgraded the toolbox for PA imaging and correlated multi-modal imaging applications.