One‐Electron‐Reduced and ‐Oxidized Stages of Donor‐Substituted 1,1,4,4‐Tetracyanobuta‐1,3‐dienes of Different Molecular Architectures

Abstract

A series of monomeric and oligomeric donor-substituted 1,1,4,4-tetracyanobuta-1,3-dienes (TCBDs) with various topologies have been synthesized by means of thermal [2+2] cycloaddition between tetracyanoethylene (TCNE) and donor-substituted alkynes, followed by retro-electrocyclization. One-electron-reduced and -oxidized stages of the donor-substituted TCBDs were generated by chemical methods. The obtained radical anions and radical cations were studied by using electron paramagnetic resonance/electron nuclear double resonance (EPR/ENDOR) spectroscopy, supported by density functional theory (DFT) calculations. The extent of pi-electron delocalization in the paramagnetic species was investigated in terms of the EPR parameters. Despite favorable molecular orbital (MO) coefficients, the EPR results suggest that in radical anions the spin and charge are confined to the electron-withdrawing TCBD moieties on the hyperfine EPR timescale. The observed spin localization is presumably caused by an interplay between the nonplanarity of the studied pi systems, limited pi-electron conjugation, and very likely counterion effects. In radical cations, an analogous spin and charge localization confined to the electron-donating N,N-dialkylaniline moieties was found. In this case, an efficient electron delocalization is disabled by small MO coefficients at the joints between the donor and acceptor portions of the studied TCBDs.

Electrochromic Behavior of Donor-Acceptor Polymers Containing Diketopyrrolopyrrole Unit

“…The E ox values suggested that the triphenylamine derivatives are stronger donors than the fluorene unit and that the substitution of the methoxy group at the para-position with respect to the nitrogen atom facilitated the oxidation, whereas the cyano group substitution made it more difficult. This result is consistent with the redox behavior of the reported triphenylamine oligomers and polymers without the DPP unit [29][30][31][32][33]. In contrast, the E red values originating from the DPP unit were not affected by the electron-donating comonomer structures.…”

Star-Shaped Conjugated Systems

“…They were applied as precursors for metallofullerene synthesis [97] or CT-Chromophores [151,152]. In one example a cyanophenyl capped derivative were employed to produce porous MOFs with silver salts [85].…”

“…However such structures are apparent as substructures in highly fluorescent materials [99] and CT-chromophores [151,152]. …”

Comparative theoretical and experimental analysis of hydrocarbon σ-radical cations

“…Recording of their electronic spectra is possible when characteristic absorption bands are intrinsic to radical cations [9]. Magnetic resonance methods are more informative, but their application is limited by short lifetime of radical cation intermediates [10]. Unfortunately, most available methods are almost inapplicable to extremely unstable hydrocarbon σ-radical cations, and only a few examples of such studies have been reported [11].…”