A First Series of Dimeric Porphyrins Electrochemically Linked with Diphosphonium Bridges

Abstract

The synthesis of dimeric porphyrins with a diphosphonium bridge in a direct one‐pot electrochemical reaction is reported. The variation in the yields of this coupling reaction depends on the conditions of the electrolysis, and was examined mainly with respect to the detected by‐products. An interpretation of this selective formation of dimers is proposed. Monomers and trimers were also obtained. These new compounds were characterized by 1H NMR, 31P NMR, UV/Vis spectroscopy and microanalysis. Important excitonic interactions were observed when the two porphyrin chromophores were linked with a short diphosphonium bridge. The NMR‐spectroscopic data suggest that isomers are present in solution. Electrochemical data indicate that the two phosphonium groups of the bridge are not electrochemically independent in the zinc dimers.

Bisporphyrins with Bischlorin Features Obtained by Direct Anodic Coupling of Porphyrins

“…An unexpected feature in the reduction of the dimers was the alternated sequence in the sites of the electron transfers respective to the chlorin‐like analogues or porphyrins and to the spacer. In contrast to the previous results,19–21 in the present dimers electrons are added first to the chromophore subunits. The first and the third two‐electron reductions generated π‐radical anions and dianions.…”

“…This bathochromic shift resulted from the electron‐withdrawing effect22–23 of the phosphonium cation linked to the β position on the porphyrin ring. The shifts of the Soret bands were similar to those already reported for other β ‐substituted porphyrins 18–21…”

“…The interesting feature in the dimers is the easy reduction of the two porphyrin rings, which occurs at very low potentials before the reduction of the diphosphonium spacer, at variance with previous results with others spacers 19–21. This specific behavior may be ascribed to the partial delocalization onto the porphyrin rings of the two positive charges carried by the spacer, in agreement with the proposed structure of a chlorin‐like compound supported by the UV‐visible and NMR results.…”

Bisporphyrins with Bischlorin Features Obtained by Direct Anodic Coupling of Porphyrins

“…An unexpected feature in the reduction of the dimers was the alternated sequence in the sites of the electron transfers respective to the chlorin‐like analogues or porphyrins and to the spacer. In contrast to the previous results,19–21 in the present dimers electrons are added first to the chromophore subunits. The first and the third two‐electron reductions generated π‐radical anions and dianions.…”

“…This bathochromic shift resulted from the electron‐withdrawing effect22–23 of the phosphonium cation linked to the β position on the porphyrin ring. The shifts of the Soret bands were similar to those already reported for other β ‐substituted porphyrins 18–21…”

“…The interesting feature in the dimers is the easy reduction of the two porphyrin rings, which occurs at very low potentials before the reduction of the diphosphonium spacer, at variance with previous results with others spacers 19–21. This specific behavior may be ascribed to the partial delocalization onto the porphyrin rings of the two positive charges carried by the spacer, in agreement with the proposed structure of a chlorin‐like compound supported by the UV‐visible and NMR results.…”

Supramolecular Assemblies Obtained by Large Counteranion Incorporation in a Well-Oriented Polycationic Copolymer

“…Analogous observations have already been described . Although the nucleophilic attack could occur on the π-cation radical as discussed previously, this reaction was not detected during cyclic voltammetry experiments, because its kinetics was too slow. ,,

1 Left: The atomic force micrograph (AFM) of 2-poly-Zn on an ITO electrode. Right: Cyclic voltammograms recorded during electropolymerization of 2-Zn in CH 3 CN/1,2-C 2 H 4 Cl 2 (1:4) performed in the potential range −0.9 V, +1.9 V vs SCE.

…”

Azolium‐Porphyrin Electrosynthesis

“…For more than a decade, our group has been interested in the electrochemical transformation of porphyrins, [5] especially in the oxidative functionalization of the porphyrin ring. We have shown, like others, [6][7][8][9][10][11] that the porphyrin core can be efficiently and (regio)selectively functionalized with different nucleophiles (pyridine, [6][7][8][9][10][11] triphenylphosphine, [9,12] nitrite, [13,14] chloride… [13,15] ) by electrochemical oxidation. The reaction mechanism involves the electrochemical oxidation of the porphyrin ring affording its cation radical, the nucleophilic attack of the nucleophile on the porphyrin, the re-oxidation of the resulting intermediate and finally the re-aromatization via the loss of a proton.…”

Bisporphyrins with Bischlorin Features Obtained by Direct Anodic Coupling of Porphyrins

“…An unexpected feature in the reduction of the dimers was the alternated sequence in the sites of the electron transfers respective to the chlorin‐like analogues or porphyrins and to the spacer. In contrast to the previous results,19–21 in the present dimers electrons are added first to the chromophore subunits. The first and the third two‐electron reductions generated π‐radical anions and dianions.…”

“…This bathochromic shift resulted from the electron‐withdrawing effect22–23 of the phosphonium cation linked to the β position on the porphyrin ring. The shifts of the Soret bands were similar to those already reported for other β ‐substituted porphyrins 18–21…”

“…The interesting feature in the dimers is the easy reduction of the two porphyrin rings, which occurs at very low potentials before the reduction of the diphosphonium spacer, at variance with previous results with others spacers 19–21. This specific behavior may be ascribed to the partial delocalization onto the porphyrin rings of the two positive charges carried by the spacer, in agreement with the proposed structure of a chlorin‐like compound supported by the UV‐visible and NMR results.…”

Supramolecular Assemblies Obtained by Large Counteranion Incorporation in a Well-Oriented Polycationic Copolymer

“…Analogous observations have already been described . Although the nucleophilic attack could occur on the π-cation radical as discussed previously, this reaction was not detected during cyclic voltammetry experiments, because its kinetics was too slow. ,,

1 Left: The atomic force micrograph (AFM) of 2-poly-Zn on an ITO electrode. Right: Cyclic voltammograms recorded during electropolymerization of 2-Zn in CH 3 CN/1,2-C 2 H 4 Cl 2 (1:4) performed in the potential range −0.9 V, +1.9 V vs SCE.

…”

Azolium‐Porphyrin Electrosynthesis

“…For more than a decade, our group has been interested in the electrochemical transformation of porphyrins, [5] especially in the oxidative functionalization of the porphyrin ring. We have shown, like others, [6][7][8][9][10][11] that the porphyrin core can be efficiently and (regio)selectively functionalized with different nucleophiles (pyridine, [6][7][8][9][10][11] triphenylphosphine, [9,12] nitrite, [13,14] chloride… [13,15] ) by electrochemical oxidation. The reaction mechanism involves the electrochemical oxidation of the porphyrin ring affording its cation radical, the nucleophilic attack of the nucleophile on the porphyrin, the re-oxidation of the resulting intermediate and finally the re-aromatization via the loss of a proton.…”

Bisporphyrins with Bischlorin Features Obtained by Direct Anodic Coupling of Porphyrins

“…An unexpected feature in the reduction of the dimers was the alternated sequence in the sites of the electron transfers respective to the chlorin‐like analogues or porphyrins and to the spacer. In contrast to the previous results,19–21 in the present dimers electrons are added first to the chromophore subunits. The first and the third two‐electron reductions generated π‐radical anions and dianions.…”

“…This bathochromic shift resulted from the electron‐withdrawing effect22–23 of the phosphonium cation linked to the β position on the porphyrin ring. The shifts of the Soret bands were similar to those already reported for other β ‐substituted porphyrins 18–21…”

“…The interesting feature in the dimers is the easy reduction of the two porphyrin rings, which occurs at very low potentials before the reduction of the diphosphonium spacer, at variance with previous results with others spacers 19–21. This specific behavior may be ascribed to the partial delocalization onto the porphyrin rings of the two positive charges carried by the spacer, in agreement with the proposed structure of a chlorin‐like compound supported by the UV‐visible and NMR results.…”

Supramolecular Assemblies Obtained by Large Counteranion Incorporation in a Well-Oriented Polycationic Copolymer

“…Analogous observations have already been described . Although the nucleophilic attack could occur on the π-cation radical as discussed previously, this reaction was not detected during cyclic voltammetry experiments, because its kinetics was too slow. ,,

1 Left: The atomic force micrograph (AFM) of 2-poly-Zn on an ITO electrode. Right: Cyclic voltammograms recorded during electropolymerization of 2-Zn in CH 3 CN/1,2-C 2 H 4 Cl 2 (1:4) performed in the potential range −0.9 V, +1.9 V vs SCE.

…”

Azolium‐Porphyrin Electrosynthesis

“…For more than a decade, our group has been interested in the electrochemical transformation of porphyrins, [5] especially in the oxidative functionalization of the porphyrin ring. We have shown, like others, [6][7][8][9][10][11] that the porphyrin core can be efficiently and (regio)selectively functionalized with different nucleophiles (pyridine, [6][7][8][9][10][11] triphenylphosphine, [9,12] nitrite, [13,14] chloride… [13,15] ) by electrochemical oxidation. The reaction mechanism involves the electrochemical oxidation of the porphyrin ring affording its cation radical, the nucleophilic attack of the nucleophile on the porphyrin, the re-oxidation of the resulting intermediate and finally the re-aromatization via the loss of a proton.…”