A series of porphyrin dimers bridged by one or two rigid arylenedioxy linkers was successfully synthesized by catalystfree meso-aryloxylation involving nucleophilic aromatic substitution. The orientational freedom and conformation of the two porphyrin macrocycles in the mono-bridged dimers depended on the steric hindrance between the macrocycles and substituents on the arylenedioxy linkers. On the other hand, the bis-bridged dimers exhibited a highly rigid cofacial conformation with a distinct interplanar distance. The fluorescence quantum yields of the bis-bridged dimers (Φ fl = 0.094 and 0.096) were quite similar to those of the monomers (Φ fl = 0.13). Owing to their high rigidities, the nonradiative deactivation of the photoexcited states associated with dimerization, which are observed for reported dimers, are mostly suppressed, thus suggesting that those dimers have highest rigidities among the cofacial porphyrin dimers exploring emission properties. Cyclic voltammetry revealed the electronic communication between the porphyrin macrocycles in the closely stacked bis-bridged dimer.

<div>Copper- and nickel-porphyrin complexes show extremely weak axial coordination ability without any electron-withdrawing groups. Herein, we report axial ligation on Cu^II- and Ni^II-porphyrins in a highly rigid cofacial porphyrin dimer with a bidentate ligand, 1,4-diazabicyclo[2.2.2]octane (DABCO). To the best of our knowledge, this is the first report on the use of Cu^II- and Ni^II-porphyrins for coordination-induced guest binding of porphyrin-based host molecules without the help of other metal ions. The high rigidity of the dimer induces guest binding through the cooperative effect of weak axial ligation. The results showed that Cu^II- and Zn^II-complexes bind one DABCO molecule inside their cavities, whereas the Ni^II-complex binds two additional DABCO molecules outside to form a stable 6-coordinate paramagnetic Ni^II-complexes. <br></div>

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<div>Copper- and nickel-porphyrin complexes show extremely weak axial coordination ability without any electron-withdrawing groups. Herein, we report axial ligation on Cu^II- and Ni^II-porphyrins in a highly rigid cofacial porphyrin dimer with a bidentate ligand, 1,4-diazabicyclo[2.2.2]octane (DABCO). To the best of our knowledge, this is the first report on the use of Cu^II- and Ni^II-porphyrins for coordination-induced guest binding of porphyrin-based host molecules without the help of other metal ions. The high rigidity of the dimer induces guest binding through the cooperative effect of weak axial ligation. The results showed that Cu^II- and Zn^II-complexes bind one DABCO molecule inside their cavities, whereas the Ni^II-complex binds two additional DABCO molecules outside to form a stable 6-coordinate paramagnetic Ni^II-complexes. <br></div>