Efficient Synthesis of Arylenedioxy‐Bridged Porphyrin Dimers through Catalyst‐Free Nucleophilic Aromatic Substitution

Abstract

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.

Outstanding Enhancement in the Axial Coordination Ability of the Highly Rigid Cofacial Cyclic Metalloporphyrin Dimer

“…The overall structure was relatively similar to that of 1 reported previously. [34] The Zn II -NDABCO bond length was ~2.20 Å, slightly longer than the Zn II -Npor bond length (~2.06 Å). The Zn ions were located 0.29-0.30 Å off the mean plane comprising four nitrogen atoms.…”

“…Bis(2,7-naphthylenedioxy)-bridged cyclic porphyrin dimer (1), [34] monobridged acyclic porphyrin dimer (2), [34] and reference monomer (3) [60] were synthesized as previously reported procedures. Chlorobenzene (PhCl) was distilled from CaH2.…”

“…(Figure 1). We have earlier reported the efficient synthesis of a cofacial porphyrin dimer bridged by two 2,7-naththyleneoxylinkers (1) [34] via catalyst-free nucleophilic aromatic substitution reactions. [35-38][39-47] This dimer has a highly rigid structure, as revealed by the diffraction and spectroscopic studies, and has an internal cavity surrounded by two porphyrin moieties with an interplanar distance of ~7.5 Å, which is suitable for binding a 1,4diazabicyclo[2.2.2]octane (DABCO) molecule.…”

Nucleophilic Aromatic Substitution (SNAr) and Related Reactions of Porphyrinoids: Mechanistic and Regiochemical Aspects

“…Porphyrin ethers have also been utilized in the generation of strapped bisporphyrin systems; more specifically cofacial porphyrin dimers (Scheme 10). Yamashita et al, [ 106 ] utilized various dihydroxyarenes and both mono‐ and trans ‐dibromo‐A 2 porphyrins to yield a variety of arylenedioxy‐bridged porphyrin dimers. As noted by the authors, there have been limited reports regarding the preparation of “closely‐stacked” porphyrin dimers, which require high dilution to be successful.…”

Outstanding Enhancement in the Axial Coordination Ability of the Highly Rigid Cofacial Cyclic Metalloporphyrin Dimer

“…(Scheme 1). We have earlier reported the efficient synthesis of a cofacial porphyrin dimer bridged by two 2,7-naththyleneoxylinkers (1) [35] via catalyst-free nucleophilic aromatic substitution reactions. [36][37][38][39][40][41][42][43][44][45][46][47][48] This dimer has a highly rigid structure, as revealed by the diffraction and spectroscopic studies, and has an internal cavity surrounded by two porphyrin moieties with an interplanar distance of ~7.5 Å, which is suitable for binding a 1,4-diazabicyclo[2.2.2]octane (DABCO) molecule.…”