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

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 d8 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.