Synthesis, characterization and properties of covalently linked porphyrin–naphthalimide pentamer and its metal complexes

• A novel porphyrin–naphthalimide pentamer was synthesized and the corresponding metal complexes were obtained.
• The porphyrin–naphthalimide pentamer 5 and its Zn complexes 6a emit intense red light.
• The fluorescence quantum yields were 0.14 and 0.08 respectively.
• Due to the efficient energy transfer, the compound 5 and 6a can act as efficient light-harvesting antennae.

A novel porphyrin–naphthalimide pentamer 5 was synthesized by linking four light-harvesting naphthalimide units to a central porphyrin, via ether bridges. The corresponding metal (Zn2+, Cu2+, Mn2+, Fe3+, Co2+) complexes 6a–6e were obtained under different reaction conditions. The structures of these compounds were characterized by 1H and 13C NMR spectra, FT-IR, MALDI-TOF-MS and elemental analysis. The photophysical properties have been investigated by UV–Vis absorption and steady-state fluorescence spectroscopy. It is found that the excitation energy transfer occurs from the naphthalimide units to the porphyrin core, and that the free base porphyrin 5 and Zn porphyrin 6a can emit intense red light. Additionally, the electrochemical properties of compounds 5 and 6a–6e were also investigated by cyclic voltammetry.

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