Zinc Complexes of Porphyrin‐Quinone Cyclophanes: Syntheses, Structures and Electron‐Transfer‐Related Properties

Abstract

Electron-transfer mechanism in metalloporphyrin-quinone cyclophanes Preparation and Characterization of Zinc Porphyrin-Quinone CyclophanesFor zinc complexation the respective metal-free porphyrin-quinone cyclophanes were heated with excess zinc acetate dihydrate in trichloromethane/methanol or in dichloromethanelmethanol. The zinc complexes were purified by MPLC on silica gel with cyclohexane/ethyl acetate and crys- EtEt tallized from trichloromethane/methanol (for details see Ex-

Distance Dependence of Photoinduced Electron-Transfer: Syntheses and Properties of Biphenylene-Spacered Porphyrin-Quinone Cyclophanes

“…The relative quantum yields Φ rel were ob-on the quinone radical anion which with increasing distance tained by dividing the integrated fluorescence bands by between porphyrin and quinone is no longer possible. This those of the corresponding porphyrin-dimethoxybenzene result is in agreement with earlier electron-transfer rate decyclophanes which for 1 to 4 are the appropriate precursors terminations [10] including X-ray structure elucidations of without, however, the capability of an intramolecular elec-zinc porphyrin-quinone cyclophanes [3] [11] . tron-transfer.…”

“…For the benzene-and naphthalene-spacered cyclo-served for the quinone protons of the zinc complexes of the benzene-and naphthalene-spacered systems (∆δ ϭ 0.47 and phanes with the shortest transannular distances, the δ values for the two hydrogen atoms on the central benzene ring 3.76, respectively), which most likely are due to an attractive interaction between the zinc ion and the carbonyl oxyare dramatically reduced from the normal value of δ ഠ 6.65 to δ ϭ 4.15 for the benzene-spacered compound, and to gen atoms of the quinones [3] [10] [11] . This high-field shift is not observed for the zinc complexes of the biphenylene-and δ ϭ 4.41 for the naphthalene-spacered analogue as a result of the porphyrin ring-current (all s, 2 H, CDCl 3 ).…”

“…the cyclophane type 1 and 2 showed by X-ray structure analyses [3] [6] [11] , and in agreement with molecular dynamics The dialdehydes 13 and 16, containing the biphenylene units linked to the central aromatic ring by the two tetra-calculations [12] , that the quinones in the cyclophane bridges are inclined towards the porphyrin plane leading to short methylene chains with all the substituents in the right places, represent the essential partial structures for building contacts between the carbonyl oxygen atoms and the zinc centre (ca. 255 pm).…”

Electron transfer reactions of rigid, cofacially compressed, π-stacked porphyrin–bridge–quinone systems

“…The [n.n]paracyclophanes define the quintessential -stacked architecture [222][223][224][225][226][227][228][229][230][231][232][233]. In cases where the methylene bridges are short (3-4 carbons), the paracylophane's arene units experience restricted rotation and are forced to adopt a stacked arrangement.…”

UV/Vis Spectra of Cyclophanes

“…As acceptors different groups such as quinones [109][110][111][112][113][114][115][116], 7,7,8,8-tetracyanoquinodimethane (TCNQ) [117], pyromellitic diimide [118], and others [119,120] were utilized. As acceptors different groups such as quinones [109][110][111][112][113][114][115][116], 7,7,8,8-tetracyanoquinodimethane (TCNQ) [117], pyromellitic diimide [118], and others [119,120] were utilized.…”