Acenequinocumulenes: Lateral and Vertical π‐Extended Analogues of Tetracyanoquinodimethane (TCNQ)

Abstract

We have designed a series of molecules and developed synthetic methodology that allows for the inclusion of structural diversity along both the lateral and vertical axes of the basic TCNQ skeleton. In the lateral direction, benzoannulation extends the π-system through (hetero)acene formation, whereas incorporation of a [3]cumulene increases delocalization vertically. The potential of these new molecules as semiconductors is explored through UV/Vis spectroscopy, cyclic voltammetry, X-ray crystallography, thin-film formation, and mobility measurements (using space charge limited current measurements).

Reverse Bond-Length Alternation in Cumulenes: Candidates for Increasing Electronic Transmission with Length

“…Oligo-quinodimethanes themselves show strong reverse decay of transmission, as the aromatic sextet of each phenyl ring is an important resonance contributor in addition to the quinoidal structure as shown in Scheme (top). , As length increases the quinodal structure loses out and diradical character increases; therefore, only few oligo-quinodimethane derivates have been successfully isolated. , The aromatic sextets promote reverse bond-length alternation when incorporated into cumulenes as shown in Scheme . Recent synthetic reports of quinoid-expanded [3]­cumulenes all display strong reverse bond alternation in the crystal structures; in all cases terminal substituent groups that can accommodate diradical character were used. − Clearly, it will be a challenge to make long oligomers of such systems; still, these are prospective systems for reverse conductance decay. Transmission calculations on such systems, included in Supporting Information part D, show clear reverse decay of transmission with length.…”

Synthesis, Characterization and Photovoltaic Properties of Electron‐Accepting (11‐Oxoanthra[2,1‐b]thiophen‐6‐ylidene)dipropanedinitrile‐Based Molecules

“…Interestingly, this conjugation and planarity are not broken for non‐fullerene acceptor ITBTC, in which the dicyanomethylene group is attached to the five‐membered cycle in 3‐oxo‐2,3‐dihydro‐1 H ‐inden‐1‐ylidene unit [27b] . This causes less distortion of the molecular structure than attaching the dicyanomethylene group to the six‐membered ring of the AT units in 3 a and similar polycyclic compounds [16c,29] . Overall, these results highlight the importance of the attaching motif of functional groups for the electron‐transport properties of organic materials.…”

Pentacenones as Divergent Intermediates to Unsymmetrically Substituted Pentacenes: Synthesis and Crystallographic Analysis

“…One strategy to unsymmetrically substitute pentacenes is to benzannulate a quinone (e.g. 1,4-anthraquinone) via step-wise Cava reactions. , Alternatively, desymmeterization can be achieved by step-wise nucleophilic ketone additions to 6,13-pentacenequinone, a common starting material toward pentacene-based materials. − Pentacenones, such as 13-hydroxy-13-(ethynylated)­pentacene-6­(13 H )-ones, have served as divergent intermediates to 6,13-unsymmetrically substituted pentacenes, related linearly- and cross-conjugated pentacene dimers, , nonconjugated dimers, and longer defined-length oligomers, as well as acenequinocumulenes and conformationally restricted dimers obtained via unusual tautomerization mechanisms (Scheme ). Access to this diverse assortment of structures has enabled the field to gain insight into charge generation and transport properties, including development of models to understand singlet fission and other related photonic processes.…”