A Synthetic Strategy for Multi-Functionalized Phospharhodamines via Catalytic P-Arylation

The visualization of complex biological events in living cells is highly reliant on the development of sophisticated fluorescent probes with multiple functions. Herein, we report a general synthetic strategy for the synthesis of near-infrared-emissive phospharhodamines (PORs) bearing various types of aryl groups on their bridging phosphorus atoms. This versatile approach utilizes a Ni-catalyzed P-arylation that allows for the design of POR-based multi-functionalized fluorescent probes. We found that PORs substituted with an aminophenyl group exhibited pH-responsive fluorescence intensity, where photo-induced electron transfer occurs to quench the fluorescence. The combination of our new approach with conventional modification at the 9-position of the xanthene skeleton facilitates the development of multi-functionalized fluorescent probes. As one demonstration of this method, we synthesized a fluorescence probe that can selectively visualize the lysosomes that result from endosomal maturation.