Switchable Closed‐Shell and Open‐Shell Biradical States in Bis‐Palladium Complexes of Tetrathiadodecaphyrin via Coordination Rearrangement

Abstract A figure‐eight tetrathiadodecaphyrin ( 1 ), featuring two porphyrin‐like sub‐pockets separated by central carbazolylenes was synthesized. Metalation of the thiaporphyrinoid ligand with Pd(OAc) 2 produces two distinct bis‐Pd(II) complexes with different coordination environments. Complex 2 , adopting an {NNCS} metalation mode, exhibits a closed‐shell electronic structure, whereas complex 3 , with an {NNCC} coordination environment, exists as a ligand‐centered organic biradicaloid with two magnetically independent spins ( S = 1/2). Biradical formation is attributed to single‐electron transfer from each ligand sub‐pocket to the Pd(II) center accommodated in a d 8 square‐planner coordination geometry. Notably, the complexes are interconvertible through doubly one‐electron redox processes, demonstrating a reversible metal coordination rearrangement via thiophene ring flipping within a porphyrinoid framework. This work establishes the first example of such tunable metal coordination, offering a precise strategy for modulating closed‐shell and open‐shell biradical states. In addition, while complex 2 displays intense absorption and photoacoustic responses to the first near‐infrared (NIR‐I) light in water after encapsulation within nanoparticles, the nanocomposites encapsulating biradicaloid 3 exhibits enhanced responsiveness in the second near‐infrared (NIR‐II) region.