A Dual-Emissive Organoplatinum(II) Probe Enables Ratiometric NIR and Phosphorescence Lifetime Imaging of Cell Membrane Integrity

Fluorescent microscopy imaging continues
to face major
challenges
due to biological scattering and autofluorescence. In this work, tridentate
platinum(II) complexes self-assemble into nanoaggregates via Pt–Pt
interactions, enabling molecular-level control over the cellular uptake
discrimination between membrane-intact and disrupted cells. This self-assembly
switches the emission character from intraligand charge transfer (ILCT)
to a lower-energy metal–metal-to-ligand charge transfer (MMLCT),
yielding a ratiometric blue-to-NIR photoluminescence response. The
emission transition is accompanied by a prolongation of the luminescence
lifetime into the microsecond regime, which facilitates concentration-independent
lifetime imaging. Furthermore, rational ligand engineering enhances
the two-photon absorption cross-sections of the complexes, supporting
their use in 3D imaging. The combination of assembly-driven two-photon
excited NIR ratiometric emission and lifetime differentiation offers
an approach for real-time monitoring of cell membrane integrity.