Synthesis and spectroelectrochemical investigation of two tetraarylporphyrins

Abstract

A free-base tetraarylporphyrin was synthesized by the [2+2] macrocyclization of a dipyrromethane derivative with 3,4,5-tris(dodecyloxy)benzaldehyde in 61% yield. The free-base porphyrin was metallated with zinc acetate in 94% conversion. The free-base and metallated porphyrins show typical intense Soret bands at 426 and 425 nm, respectively, along with the expected number and intensity of Q-bands. Both porphyrins are also fluorescent and display small Stokes shifts between 13 and 18 nm. Cyclic voltammetry established that each porphyrin underwent two reversible one-electron oxidations at 492 and 725 mV (vs Fc/Fc + (ferrocene reference)) for the free-base porphyrin and at 329 and 589 mV (vs Fc/Fc + ) for the Zn-metalloporphyrin. Electron-transfer rates were also determined to fall between 1.2 Â 10 -3 and 2.4 Â 10 -3 cm s -1 . In addition, spectroelectrochemistry and density functional theory calculations of the oxidized products were carried out to confirm the macrocyclic ring oxidations.Résumé : On a réalisé la synthèse d'une tétraaraylporphyrine sous la forme de base libre avec un rendement de 61 % par macrocyclisation [2+2] d'un dérivé de dipyrrométhane avec du 3,4,5-tris(docécyloxo)benzaldéhyde. On a effectué la métal-lation de la porphyrine à l'état de base libre, avec un rendement de 94 %, par traitement avec de l'acétate de zinc. La base libre et la porphyrine métallée présentent respectivement les bandes typiques intenses de Soret à 426 et à 425 nm ainsi que le nombre et l'intensité attendu des bandes Q. Les deux porphyrines sont aussi fluorescentes et elles présentent de faibles déplacements de Stokes, entre 13 et 18 nm. La voltampérométrie cyclique a permis d'établir que chaque porphyrine subit deux oxydations réversibles à un électron, à 492 et 725 mV (vs Fc/Fc + ) pour la base libre et à 329 et 589 mV (vs Fc/Fc + ) pour la Zn-métalloporphyrine. On a aussi déterminé que les vitesses de transfert d'électron se situent entre 1,2 Â 10 -3 et 2,4 Â 10 -3 cm s -1 . De plus, de la spectroélectrochimie et des calculs d'après la théorie de la fonctionnelle de la densité effectués sur les produits oxydés pour confirmer les oxydations des noyaux macrocycliques.Mots-clés : porphyrinoïdes, électrochimie, chimie d'oxydoréduction, photochimie, calculs de la fonctionnelle de la densité.[Traduit par la Rédaction]

Synthesis and Optical and Electronic Properties of Core-Modified 21,23-Dithiaporphyrins

“…Furthermore, both porphyrins 3 and 4 presented Q-bands that were linear in absorbance for concentrations ranging from micro- to millimolar implying minimal aggregation in DMF, and 3 showed linear absorbance behavior in methylene chloride and insignificant solvatochromic effects. Compared to tetrapyrrolic porphyrin analogues, dithiaporphyrins 3 and 4 display red-shifted absorbance maxima, and this observation is consistent with the incorporation of thiophene moieties into the aromatic core . The parent, tetraphenyldithiaporphyrin (TP-N 2 S 2 ), shows similar molar absorptivity trends with peak maxima at the following wavelengths in chloroform: 435 nm (Soret), 515 nm (Q IV), 548 nm (Q III), 635 nm (Q II), and 699 nm (Q I).…”

“…The peak currents for all of the voltammograms (see the Supporting Information for additional voltammograms of 3 and 4 ) show a linear relationship with the square root of the scan rate, which is consistent with a diffusion-controlled reaction, indicating that 3 and 4 do not physisorb to the glassy carbon electrode. Using Nicholson’s method, the electron-transfer rate constants for the quasi-reversible reduction and oxidation peaks for 3 were determined to be 1.8 × 10 –4 cm s –1 ( E red2 ), 4.0 × 10 –4 cm s –1 ( E red1 ), 4.6 × 10 –4 cm s –1 ( E ox1 ), and 3.9 × 10 –4 cm s –1 ( E ox2 ), respectively, and are similar to other dithiaporphyrins and porphyrins. , Additional electrochemical properties for 3 and 4 are summarized in Table and Table S1 in the Supporting Information.…”

“…The absorption spectrum of 4 in DMF is shown in Figure and displays a typical porphyrin profile. ,− The Soret band for 4 is at 440 nm (ε = 2.4 × 10 5 M –1 cm –1 ) with less intense Q-bands, shown in Figure inset, at 518 nm, 554 nm, 637 and 701 nm with molar absorptivities of 2.5 × 10 4 M –1 cm –1 , 1.4 × 10 4 M –1 cm –1 , 1.4 × 10 3 M –1 cm –1 , and 6.9 × 10 3 M –1 cm –1 , respectively. Expectedly, the absorption spectrum of 3 was nearly identical to 4 , and the optical data are summarized Table .…”

“…To afford the nonsymmetrically substituted meso-positions there are two approaches that could result in dithiaporphyrin 3, namely reacting 2a with 1b or reacting 2b with 1a. Interestingly, only the former reaction sequence, 2a with 1b in the presence of BF 3 etherate and DDQ, 33,36 resulted in a reasonable yield of 3 (16%). 32,35,36 By starting with 2b, en route to dithiaporphyrin 3, the Lewis acid ring-closing step with diol 1a caused meso-position scrambling.…”

Liquid crystalline 21,23-dithiaporphyrins

“…Using the method presented by Nicholson, 11 the electron transfer rate constants are 2.2 Â 10 À4 cm s À1 and 2.5 Â 10 À4 cm s À1 for the two oxidation peaks, respectively, which is similar to an analogous N 4 -porphyrin. 12 Again, porphyrin 2b exhibits similar electrochemical properties and is tabulated in the ESI. † Scheme 1 Synthesis of 21,23-dithiaporphyrins.…”