Supramolecular Inclusion Complexes of Two Cyclic Zinc Bisporphyrins with C₆₀ and C₇₀: Structural, Thermodynamic, and Photophysical Characterization

Abstract

The formation of thermodynamically stable inclusion complexes between two cyclic zinc bisporphyrins, differing in the saturation degree of the hydrocarbon linkers that connect their porphyrin units, and the fullerenes C(60) and C(70) is described. Binding and photophysical studies were performed in two solvents of very different polarity: toluene and dichloromethane. UV/Vis and fluorescence titration experiments showed π-π interactions between the cyclic zinc bisporphyrins and the fullerenes. Solid-state structures were determined by X-ray diffraction analysis and gave valuable insight into the different complexation behaviors of the two macrocyclic systems towards the fullerenes. NMR titrations were also helpful in understanding the geometry of the complexes in solution. Upon fullerene complexation, the two macrocyclic bisporphyrins adopt very distinct conformations. Charge-transfer absorption bands point to ground-state interactions, and quenching of the porphyrin component luminescence indicates fast reactivity in the excited states. Energy transfer plus HOMO-HOMO and LUMO-LUMO electron-transfer processes occur within the complexes. Charge-separated states characterized by a reduced fullerene and an oxidized porphyrin radical, with lifetimes in the order of several hundred picoseconds, are detected.

Solid-state inclusion of C60and C70in a co-polymer induced by metal–ligand coordination of a Zn–porphyrin cage with a bis-pyridyl perylene derivative

“…3 × 10 4 M -1 and 5±0.5 × 10 4 M -1 , respectively, by means of both spectrophotometric (absorption) and spectrofluorometric (emission) spectroscopic titrations. 61 We have also determined the solid-state structures of both inclusion complexes. The Zn(II)-bisporphyrin macrocycle adopts a clamshell-like conformation with the planes of the porphyrin units tilted and forming a dihedral angle in the range of 43-45°.…”

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

“…As compared to porphyrin monomers, porphyrin dimers with appropriate linkage can accommodate electron acceptor guest molecules by π-π interactions to form sandwich complexes. [86][87][88][89][90][91][92][93][94][95][96] For example, a cyclic Ni porphyrin dimer (Ni-CPD Py ) linked by butadiyne moieties bearing 4-pyridyl groups (Fig. 7) forms a sandwich complex with C 60 (C 60 ⊂ Ni 2 -CPD Py ) as shown in the X-ray crystal structure ( Fig.…”

Sponge-like molecular cage for purification of fullerenes

“…Host platforms containing extended p-systems have been designed because of their affinity towards the sphere-like unsaturated structure of fullerenes. In this line, several covalent or supramolecular approaches pursued include: (a) macrocyclic arene-based receptors [18][19][20][21][22][23][24] , (b) macrocyclic structures containing aromatic heterocycles [25][26][27][28] , (c) p-extended TTF receptors [29][30][31][32][33] and (d) macrocyclic or jawlike structures containing porphyrin moieties 17,[34][35][36][37][38][39][40][41][42][43][44][45] . Interestingly, Fujita and co-workers reported the use of the empty channels of a metal-organic framework (MOF) for encapsulating fullerenes upon soaking MOF crystals in fullerene-containing toluene.…”