Visualization of nonemissive triplet species of Zn(II) porphyrins through Cu(II) porphyrin emission via the reservoir mechanism in a porphyrin macroring

A macroring composed of three Cu(II) porphyrins (CuP) and three slipped-cofacial Zn(II) porphyrin (ZnP_2) dimers exhibited near-IR emission from the CuP part. The emission lifetime of the macroring (15 μs) was 500 times longer compared to that of a Cu porphyrin monomer (e.g., Cu(II)TPP; TPP = meso -tetraphenylporphyrin). The observed emission is ascribed to emission via the reservoir mechanism from the trip-doublet (^2T_1) state in CuP thermally activated from the T_1 state of ZnP_2, which is located ca. 1030 cm^−1 below the ^2T_1 state of CuP. The near-IR emission of the macroring was significantly quenched by O_2, whereas that of the Cu porphyrin monomer was hardly quenched, indicating that the quenching event mainly occurred on the T_1 state of the ZnP_2 parts. The nonemissive triplet state of a Zn porphyrin at room temperature was visualized through emission from a neighboring Cu porphyrin.

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