Greatly Enhanced Intermolecular π‐Dimer Formation of a Porphyrin Trimer Radical Trications through Multiple π Bonds

Abstract

A trefoil-like porphyrin trimer linked by triphenylamine (TPA-TPZn(3)) was synthesized. A three-electron oxidation of TPA-TPZn(3) forms a radical trication (TPA-TPZn(3)(3+)), in which each porphyrin ring undergoes a one-electron oxidation. The radical trication TPA-TPZn(3)(3+) spontaneously dimerizes to afford (TPA-TPZn(3))(2)(6+) in CH(2)Cl(2) . The characteristic charge-resonance band due to the charge delocalization over the π system of (TPA-TPZn(3))(2)(6+) was observed in the NIR region. The initial oxidation potential of TPA-TPZn(3) is negatively shifted relative to that of the corresponding monomer porphyrin, which results from the stabilization of the oxidized state of TPA-TPZn(3) associated with the dimerization. The thermodynamic parameters (i.e., ΔH, ΔS, and ΔG) for the formation of (TPA-TPZn(3))(2)(6+) were determined by measuring Vis/NIR spectra at various temperatures. The formation constant of (TPA-TPZn(3))(2)(6+) is significantly larger than that of the radical cation dimer of the corresponding monomer porphyrin (e.g., over 2000-fold at 233 K). The electronic states were investigated using EPR spectroscopic analysis. The greatly enhanced dimerization of TPA-TPZn(3)(3+) results from multiple π-bond formation between the porphyrin radical cations.

Acid-Responsive Conductive Nanofiber of Tetrabenzoporphyrin Made by Solution Processing

“…Visible−near-infrared (vis−NIR) spectroscopy provided further evidence of electron delocalization through the BP columnar stacka very broad peak in the NIR region of 1500− 2500 nm (Figure 2f), which we assign to a charge-resonance band because of electron delocalization among tightly π-stacked BP molecules. 25,26 The significantly blue-shifted (against neutral BP) Soret band peaked at 396 nm and the Q-band peaked at 594 nm are also characteristic.…”

Long-lived photoinduced charge separation for solar cell applications in supramolecular complexes of multi-metalloporphyrins and fullerenes

“…•+ ). 113,116,117 In sharp contrast to the TPZn 3 -PyC 60 complex, the transient absorption spectrum of the monomer porphyrin (MPZn) in the presence of PyC 60 (Fig. 13b) exhibits the absorbance change due to the energy transfer from 1 MPZn* to PyC 60 to give the singlet excited state 1 PyC 60 * (1.76 eV), followed by the conversion to the triplet excited states 3 MPZn* and 3 PyC 60 * at 2800 ps (green line in Fig.…”

Interactions of Metal-Based and Ligand-Based Electronic Spins in Neutral Tripyrrindione π Dimers

“…The interaction of delocalized π radicals − to form cofacial dimers and stacked architectures is an important aspect of the chemistry of stable organic radicals − and of several metal complexes of redox-active ligands hosting unpaired electrons. − In recent years, π–π interactions have been incorporated in the design of functional molecular materials featuring tunable optical and conductive properties. − In biology, π–π interactions between tetrapyrrolic macrocycles are key to numerous electron-transfer processes, such as those originating at the bacteriochlorophyll dimer ( special pair ) in bacterial photosynthetic reaction centers. , Inspired by the combination of π–π electronic interactions and one-electron redox chemistry in biological tetrapyrroles, the chemistry of π dimers of porphyrin radical cations − continues to attract considerable attention. − Herein, we document the first characterizations in solution of neutral π dimers featuring ligand-based radicals on tripyrrolic complexes.…”