Cyclic Porphyrin Dimers with a Slipped Cofacial Arrangement Through Coordination Linkage of Phosphine Oxide Substituents with Yb(III) and Lu(III) Complexes

Porphyrin derivatives have been widely studied as models for (bacterio)chlorophyll pigments, and various dimeric architectures have been constructed through covalent or noncovalent bonds to mimic the special pairs found in photosynthetic reaction centers. Herein, novel cyclic porphyrin dimers are reported that are formed through the coordination between meso-substituted porphyrins bearing two phosphine oxide groups and lanthanide complexes, Ln(hfa)₃ (Ln = Yb, Lu; hfa = hexafluoroacetylacetonate). Single-crystal X-ray analysis of the Yb(III) complex revealed a slipped cofacial arrangement, in which two porphyrin units are bridged by Yb(III) centers via phosphine oxide coordination, closely resembling natural special pairs. The resulting dimers are stable in toluene and exhibit broadened Soret bands and redshifted Q bands compared to the monomeric porphyrin ligand. Upon porphyrin photoexcitation, the Yb(III) complex shows near-infrared luminescence from the Yb(III) center, while the porphyrin fluorescence intensity is essentially unaffected, demonstrating potential for oxygen sensing (Φ_Yb(Ar)/Φ_Yb(air) = 4.8). Transient absorption measurements confirmed the extended T₁ lifetime of the porphyrin units within the dimer structure. The dimers also show enhanced photostability under blue-light irradiation compared to the monomer. This study presents the first example of the Yb(III)-coordinated slipped cofacial porphyrin dimer with ratiometric oxygen-sensing capability and high photostability.