Ferrocenyl‐Ended Thieno–Vinylene Oligomers: Donor–Acceptor Polarization and Mixed‐Valence Properties with Emphasis on the Raman Mapping of Localized‐to‐Delocalized Transitions

Abstract

What's your role? New oligothiophene-vinylene compounds have been synthesized to study the role of the conjugated chain in two different cases (see scheme; MV=mixed valence). The electronic and molecular structures were analyzed by means of electronic, X-ray photoelectron, and Raman spectroscopy, together with thermo spectroscopy, electrochemistry, and DFT calculations.New oligothiophene-vinylene compounds have been synthesized in order to study the role of the conjugated chain in two different cases: 1) when push-pull action operates between an electron-donor and an electron-acceptor group at the ends of the thiophene-vinylene conjugated chain, and 2) when mixed-valence action is induced by single oxidation of the same chain functionalized at both terminal positions with ferrocene groups leading to competition between the donor groups. The electronic and molecular structures are analyzed by means of electronic, X-ray photoelectron and Raman spectroscopies, together with thermospectroscopy, electrochemistry and density functional theory calculations. The cyclic voltammetry processes have been followed by spectrochemistry. It is shown that the radical cation of the diferrocenyl derivative is a class III mixed-valence system (i.e., fully delocalized) according to its Raman spectrum. Moreover, by Raman thermo-spectroscopy the thermal transition of this radical cation from a delocalized (class III, room temperature) to a localized (class II, -160 degrees C) state is scanned. In all cases the Raman study is paralleled by an electronic absorption spectroscopic analysis. Structure-property relationships are proposed for molecules of two important fields of very active research as that of the non-linear optics (i.e., organic optoelectronic) and that of the mixed-valence systems (i.e., charge-transfer processes).

Robust Ethylenedioxythiophene–Vinylene Oligomers from Fragile Thiophene–Vinylene Cores: Synthesis and Optical, Chemical and Electrochemical Properties of Multicharged Shapes

“…For 3 EDOT, only two stable oxidation potentials were measured, [12] which appear at higher potentials than the ones for 3 EDOTV, which is in line with the greater p space of the later imparted by the intercalation of vinylene bonds (see DE values in Table 2). For 4 TV, [5,17] the DE value between the dicationic and the cationic oxidation potentials was measured to be 0.2 V, which is larger than 0.17 V, which was measured for our 4 EDOTV sample, revealing the stabilising effect of the EDO groups for the oxidised species. There is a good linear fit of the first two oxidation potentials with the reciprocal of the chain length (see Figure S25 in the Supporting Information) for the three n EDOTV compounds indicating that the major role in the stabilisation of the positive charge is imparted by the conjugated C=C/CÀC bond sequence.…”

Delocalization-to-Localization Charge Transition in Diferrocenyl-Oligothienylene-Vinylene Molecular Wires as a Function of the Size by Raman Spectroscopy

“…This work presents the preparation of a series of medium to large size oligothiophene-vinylene oligomers (Scheme and Supporting Information) in which the delocalized/localized property is introduced in the radical cation state by two end-capping ferrocenes, thus mimicking the M–B–M structural formula. For comparisons, the same oligothiophenes-vinylene oligomers without ferrocenes are also studied (Scheme ).…”

Delocalization-to-Localization Charge Transition in Divinylthiophene-Bridged Biruthenium Complexes as a Function of Length of the Bridging Chain by Both IR Spectroscopy and Theoretical Investigations

“…Wenger et al designed and synthesized an organic mixed valence system using α,α′-bis­(diphenylamino) units as redox termini and studied the electronic coupling properties of oligothiophene derivatives. , Chen et al, Liu et al, , and Patra et al have reported bis­(ethynyl)­oligothiophene-bridged biruthenium complexes and investigated their electrochemical and spectroscopic properties in different redox states. The delocalized-to-localized charge transitions in thieno-vinylene oligomers with ferrocene as the redox active unit were studied using Raman spectroscopy. , Gidron and Bendikov reported that biferrocenyl-capped oligothiophenes offer slightly weaker electronic coupling than oligofurans. , Sato et al previously also reported mixed valence systems containing biferrocenyl-capped oligothiophenes, but without quantitative discussion on charge delocalization in such systems. , Despite the extensive work in the field, systematic studies on the influence of oligothiophenes of various chain lengths on the electronic delocalization in bimetallic mixed valence complexes [ML n (bridge)­ML n ] + are still scarce.…”

“…The delocalized-to-localized charge transitions in thieno-vinylene oligomers with ferrocene as the redox active unit were studied using Raman spectroscopy. 22,23 Gidron and Bendikov reported that biferrocenyl-capped oligothiophenes offer slightly weaker electronic coupling than oligofurans. 24,25 Sato et al previously also reported mixed valence systems containing biferrocenyl-capped oligothiophenes, but without quantitative discussion on charge delocalization in such systems.…”