Quinoidal oligothiophenes: new properties behind an unconventional electronic structure

Abstract

The main chemical, spectroscopic and material research done in tetracyano quinoidal oligothiophenes in the last 30 years has been reviewed. Their use as semiconducting substrates in organic electronic and their versatility to act as multifunctional materials have been highlighted. This tutorial review has been paralleled by the description of the main findings provided by Raman spectroscopy, in particular, associated with the discovery of the intrinsic diradical properties inherent to the pro-aromatic character of the quinoidal arrangement. It turns out that the fascinating properties of these materials are the manifestation of the diradical fingerprint behind a rather unconventional electronic structure.

Thermally controlling the singlet–triplet energy gap of a diradical in the solid state

“…Estimation, determination and the control of the singlet–triplet energy gap have thus become the central themes in the study of diradicals. 1–10 The use of different substituents and incorporation of heteroatoms in the structures have proven effective ways to alter the energy gap. However, control of Δ E ST of a crystalline diradical by external stimuli (temperature, pressure, light, etc. )…”

Progress in side-chain thiophene-containing polymers: synthesis, properties and applications

“…Polythiophenes, oligothiophenes and their functional derivatives are among the most frequently used -conjugated materials as active components in organic electronics [9][10][11][12][13][14]. Among thiophene-based polymeric materials, thiophene moieties are generally placed in the main-chain architecture.…”

Corrigendum: An Unusually Small Singlet–Triplet Gap in a Quinoidal 1,6‐Methano[10]annulene Resulting from Baird's 4n π‐Electron Triplet Stabilization

“…[3] Tw oc ommon motifs for these molecules are extended polycyclic aromatic frameworks [4][5][6][7] and conjugated oligomers with terminal dicyanomethylene groups (e.g.Q nTCN, Scheme 1). [8][9][10] Molecules with extended quinoidal structures often exhibit strong electron-accepting behavior,w ith electron mobilities well over 1cm 2 V À 1 s À 1 . [11,12] These quinoidal platforms typically have ap roaromatic character,w hich makes them convertible into aromatic moieties,t hus opening ad ichotomy of closed-shell quinoidal or open-shell diradical structures (Scheme 1).…”

“…[11,12] These quinoidal platforms typically have ap roaromatic character,w hich makes them convertible into aromatic moieties,t hus opening ad ichotomy of closed-shell quinoidal or open-shell diradical structures (Scheme 1). [9] Thel atter are characterized by singlet electronic ground states because of double spin polarization (DSP), which preferably stabilizes the singlet over the triplet diradical state and thus controls the singlet-triplet energy gap (DE ST in Scheme 1). [9] Thel atter are characterized by singlet electronic ground states because of double spin polarization (DSP), which preferably stabilizes the singlet over the triplet diradical state and thus controls the singlet-triplet energy gap (DE ST in Scheme 1).…”