Dye Stacking Goes Beyond Single-Molecule Photocatalysis: Modifying Twisted Segregated Stacking of Dyes in Coordination Polymers for Multiphoton-Driven Potent Reduction and Oxidation

Supreme photoreductive and photooxidative potentials are important for single-electron activation of inert bonds. A consecutive two-photon excitation of a neutral dye and its radical cation can theoretically achieve potent photoreductive and photooxidative driving forces. However, the sluggish generation of key radical cationic intermediates and their low concentrations do not favor second-photon excitation. Moreover, the extremely short lifetime of excited-state radical cations and the mutual interference between reductive and oxidative species raise controversial kinetic requirements that are difficult to realize in homogeneous mode. To circumvent these dilemmas, herein, we modified the 10-phenylphenothiazine dye core into a coordination polymer through a twisted donor–acceptor (D-A) segregated stacking manner. This stacking mode retarded the recombination of D•+ and A•– after the first photoexcitation and facilitated the long-range delocalization of separated carriers. This system not only stabilized and accumulated the key radical cationic intermediates to promote second-photon excitation but also circumvented the mutual disturbance between photoreductive and photooxidative processes, promoting the accessibility of extremely short-lived photooxidative centers toward substrates during second photoexcitation. This protocol went beyond the limitations of single-molecule photocatalysis, which effectively exploited the potent photoreduction of cyanoarenes and the potent photooxidation of alkylarenes/carboxylates in one pot, directly achieving C(sp3)-C(sp2) radical cross-coupling with added value and pharmaceutical interests.