Four-Photon Absorption Iron Complex for Magnetic Resonance/Photoacoustic Dual-Model Imaging and an Enhanced Ferroptosis Process.

Four-photon absorption (4PA) multimodal therapeutic agent applied to tumor ferroptosis process tracking is rarely reported. In this paper, two functionalized terpyridine iron complexes ( TD-FeCl 3 , TD-Fe-TD ) with four-photon absorption properties were designed and synthesized. The four-photon absorption cross sections of TD-FeCl 3 reached 6.87 × 10 -74 cm 8 ·s 3 ·photon -3 . Due to its strong near-infrared absorption, TD-FeCl 3 has excellent photoacoustic imaging (PAI) capability for accurate PA imaging. TD-FeCl 3 has an efficient longitudinal electron relaxation rate ( r 1 = 2.26 mM -1 s -1 ) and high spatial resolution, which can be applied as T 1 -weighted magnetic resonance imaging (MRI) contrast agent for tumor imaging in vivo . In addition, Fe 3+ as a natural ferroptosis tracer, TD-FeCl 3 , is able to deplete glutathione (GSH) effectively, which can further enhance the ferroptosis process. We found that the series of cheap transition metal complexes has four-photon absorption activity and can be used as multimodal (MRI/PAI) diagnostic agents for tumor tracing processes.