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The peripheral nitrogen of N-confused porphyrins (NCP) can serve as a hydrogen bonding donor and acceptor, and a metal coordination site as well. NCP forms versatile dimers with the assistance of metal ions such as Pd^II, Pt^II, Zn^II, Cd^II, Hg^II, Mn^II and Fe^II. The square-planar divalent metal complexes of C₆F₅-substituted NCP with Cu^II, Ni^II and Pd^II act as efficient anion binding receptors. The doubly N-confused porphyrins (N₂CP), possessing both N and NH at the periphery, form self-assembled 1-D hydrogen bonding networks, whose orientations differ in cis (zigzag) and trans (straight) isomers.

A hexapyrrane P6 with a terminal N-confused pyrrole was synthesized by acid-catalyzed [3+3] condensation followed by oxidation with DDQ, which did not afford the expected N-confused hexaphyrin. In stead, a rearranged product, i.e., $\alpha$-dipyrrin appended N-confused porphyrin 1 was obtained in a yield of 46%. Chelation of 1 with Pt(II) afforded the peripheral complex 1-Pt, which was further coordinated with Rh(I) in the cavity to afford the corresponding bimetallic complex 1-Pt-Rh. Both 1-Pt and 1-Pt-Rh exhibit split Soret-like bands and noticeable Q-like bands tailing to the NIR region up to ca. 1200 nm. Single crystal X-ray diffraction analyses of 1 and 1-Pt revealed that the peripheral coordination of Pt(II) slightly modifies the interplanar angle between the porphyrin macrocycle and the dipyrrin unit, which may modulate the absorption spectra. The results of this work compose an interesting example of synthesizing porphyrinoids appended with conjugated peripheral chains by the oxidative ring closure reaction of an oligopyrrane containing a terminal N-confused pyrrole, and such compounds may be used for both inner and peripheral coordination to afford complexes with tunable NIR absorption.

With the purpose to develop long chain-conjugated oligopyrrin-like compounds and their metal complexes, and thus achieve tunable near-infrared absorption, a dithienyl-blocked hexapyrrane ${\mathrm{\text{S}}}_2-{\mathrm{\text{P}}}_6$ was synthesized by acid-catalyzed [2+4+2] condensation, followed by oxidation with DDQ to afford dithiaoctapyrrin 1, and its mononuclear metal complexes 1-Cu and 1-Zn were synthesized by treating 1 with Cu(II) and Zn(II) acetates. All the compounds were systematically characterized by NMR/EPR, and HRMS. The crystal structures revealed that 1 adopts a double hook-like conformation. Whereas, both complexes 1-Cu and 1-Zn adopt spiral-hook hybrid conformations, showing smaller interplanar angles between the rings within the spiral part, compared with those in the hook-like counterpart of molecule 1, which is favorable for red-shifting the absorption. As expected, the absorption band edges for complexes 1-Cu and 1-Zn are red-shifted to ca. 1560 nm, compared with that of 1260 nm observed for 1.