Tetrathia[7]helicene-Based Complexes of Ferrocene and (η⁵-Cyclohexadienyl)tricarbonylmanganese: Synthesis and Electrochemical Studies

Tetrathia­[7]­helicene ([7]­TH)-based complexes substituted at the thienyl ring ends by a ferrocenyl group (Fc) or by a (η⁵-cyclohexadienyl)­Mn­(CO)₃ derivative have been prepared by Sonogashira coupling reactions starting from the mono- or diiodo [7]­TH compounds. The molecular structure of one of the diferrocenyl [7]­TH complexes was established by X-ray analysis. Electrochemical investigation on the Fc-[7]­TH systems show that the Fc groups are significantly electron poorer with respect to Fc (Δ<i>E</i>° ≈ 0.15 V), due to the effective conjugation of the Fc redox moiety with the triple bond + helicene system, as also confirmed by spectroscopic data. Potential cycling around the second oxidation peak, assigned to the thiahelicene moiety, affords fast, regular growth of electrodeposited conducting films, provided that one terminal α-thiophene position be available for coupling; on the other hand, long alkyl chains hamper film formation. The conducting films feature a broad oxidation wave resulting from the merging of several redox peaks, having its onset at the Fc oxidation. Since conducting films obtained by electrooligomerization of parent tetrathiahelicene have their onset potentials 0.45 V more positive than the Fc redox sites in this studied Fc-[7]­TH conjugates, the above continuity could point to some coupling between Fc redox centers and conjugated π systems, favored by solid-state stacking

Tetrathia[7]helicene-Based Complexes of Ferrocene and (η⁵-Cyclohexadienyl)tricarbonylmanganese: Synthesis and Electrochemical Studies

Tetrathia­[7]­helicene ([7]­TH)-based complexes substituted at the thienyl ring ends by a ferrocenyl group (Fc) or by a (η⁵-cyclohexadienyl)­Mn­(CO)₃ derivative have been prepared by Sonogashira coupling reactions starting from the mono- or diiodo [7]­TH compounds. The molecular structure of one of the diferrocenyl [7]­TH complexes was established by X-ray analysis. Electrochemical investigation on the Fc-[7]­TH systems show that the Fc groups are significantly electron poorer with respect to Fc (Δ<i>E</i>° ≈ 0.15 V), due to the effective conjugation of the Fc redox moiety with the triple bond + helicene system, as also confirmed by spectroscopic data. Potential cycling around the second oxidation peak, assigned to the thiahelicene moiety, affords fast, regular growth of electrodeposited conducting films, provided that one terminal α-thiophene position be available for coupling; on the other hand, long alkyl chains hamper film formation. The conducting films feature a broad oxidation wave resulting from the merging of several redox peaks, having its onset at the Fc oxidation. Since conducting films obtained by electrooligomerization of parent tetrathiahelicene have their onset potentials 0.45 V more positive than the Fc redox sites in this studied Fc-[7]­TH conjugates, the above continuity could point to some coupling between Fc redox centers and conjugated π systems, favored by solid-state stacking

Tetrathia[7]helicene-Based Complexes of Ferrocene and (η⁵-Cyclohexadienyl)tricarbonylmanganese: Synthesis and Electrochemical Studies

Tetrathia­[7]­helicene ([7]­TH)-based complexes substituted at the thienyl ring ends by a ferrocenyl group (Fc) or by a (η⁵-cyclohexadienyl)­Mn­(CO)₃ derivative have been prepared by Sonogashira coupling reactions starting from the mono- or diiodo [7]­TH compounds. The molecular structure of one of the diferrocenyl [7]­TH complexes was established by X-ray analysis. Electrochemical investigation on the Fc-[7]­TH systems show that the Fc groups are significantly electron poorer with respect to Fc (Δ<i>E</i>° ≈ 0.15 V), due to the effective conjugation of the Fc redox moiety with the triple bond + helicene system, as also confirmed by spectroscopic data. Potential cycling around the second oxidation peak, assigned to the thiahelicene moiety, affords fast, regular growth of electrodeposited conducting films, provided that one terminal α-thiophene position be available for coupling; on the other hand, long alkyl chains hamper film formation. The conducting films feature a broad oxidation wave resulting from the merging of several redox peaks, having its onset at the Fc oxidation. Since conducting films obtained by electrooligomerization of parent tetrathiahelicene have their onset potentials 0.45 V more positive than the Fc redox sites in this studied Fc-[7]­TH conjugates, the above continuity could point to some coupling between Fc redox centers and conjugated π systems, favored by solid-state stacking

Physicochemical Investigation of the Panchromatic Effect on β‑Substituted Zn^II Porphyrinates for DSSCs: The Role of the π Bridge between a Dithienylethylene Unit and the Porphyrinic Ring

Three novel dyes based on Zn^II porphyrinates combined, in β-pyrrolic position, with the π unit dithienylethylene (DTE) have been synthesized and investigated for application in DSSCs. The panchromatic effect due to elongation of the π-delocalized system through a bridge between the porphyrinic ring and the DTE unit such as the 4-ethynylstyryl (<b>1</b>), ethynyl (<b>2</b>), and ethenyl (<b>3</b>) bonds have been investigated by computational, electrochemical, and photoelectrochemical methods. For all three dyes the π conjugated substituents in the β position produced the expected panchromatic effect with broadened electronic absorption spectra over a wide range of wavelengths and IPCE spectra featuring a broad plateau in the region 430–650 nm. In addition both DFT computational and electrochemical data have shown a smaller HOMO–LUMO energy gap for dye <b>3,</b> when compared to dye <b>2</b> suggesting a slightly more facile conjugation between the porphyrinic core and the DTE unit through the ethenylic bond. Conversely the photoelectrochemical investigation showed improved DSSC performances from <b>3</b> to <b>1</b>. These results have been rationalized by an in-depth DFT computational study of dyes <b>2</b> and <b>3</b> interacting with a cluster of 82 TiO₂ units. The small energetic overlap between the LUMO and the TiO₂ conduction band characterizing the more structurally distorted dye <b>3</b> would suggest low quantum yield of electron injection, while dye <b>2</b> shows a greater interaction between the LUMO of the dye and the semiconductor. Consequently the increased linearity and planarity of the structure of dye <b>1</b> seems to be the origin of its best performance in DSSC. Therefore it appears that the nature of the bridge between the DTE unit and the porphyrinic ring is quite relevant for the efficiency of these dyes for DSSC, due to distortion from the planarity and linearity of the structure of the dye and the consequent changes on the dye π conjugation