Conjugation and optoelectronic properties of acetylenic scaffolds and charge-transfer chromophores

Abstract

Our group started a research program in acetylene chemistry in 1987; since then, an intense research effort led to a fascinating journey into acetylenic scaffolding, aimed at exploring conjugative and optoelectronic properties of acetylenic chromophores. This journey included the generation of a unique molecular construction kit for acetylenic scaffolding, consisting of (E)-1,2-diethynylethenes [DEEs, (E)-hex-3-ene-1,5-diynes], tetraethynylethenes (TEEs, 3,4-diethynylhex-3-ene-1,5-diynes), chiral 1,3-diethynylallenes (DEAs, hepta-3,4-diene-1,6-diynes), 1,4-di and 1,1,4,4-tetraethynylbutatrienes, chiral trialkynylmethanes, and 1,1,2,2-tetraethynylethanes. These building modules were subsequently applied to the synthesis of carbon-rich architectures extending into one, two, and three dimensions. They include multinanometer-long monodisperse oligomers as models for infinite acetylenic polymers, molecular switches, perethynylated dehydroannulenes, expanded radialenes, and radiaannulenes, and an octamethoxy-substituted expanded cubane with a central C 56 core. Donor-substituted cyanoethynylethenes (CEEs) and 1,1,4,4-tetracyanobuta-1,3-dienes (TCBDs) were introduced as new push-pull chromophores featuring intense intramolecular charge-transfer (CT) interactions. Dendritic multivalent CT chromophores were constructed using atom-economic, "click"-like reactions, and these systems were shown to behave as "molecular batteries", featuring exceptional electron uptake and storage capacity. The research finally led to the development of an unprecedented cascade reaction for the preparation of dendritic and oligomeric donor-acceptor (D-A) molecules. New [AB]-type oligomers become accessible in domino reactions involving repetitive sequences of [2+2] cycloadditions of tetracyanoethylene (TCNE) and tetrathiafulvalene (TTF) to polyynes, followed by retro-electrocyclizations.

Nanostructured Carbonaceous Materials from Molecular Precursors

“…[134] Concurrently, Sygula and Rabideau published a similar approach, [135] and further refinement of the synthetic protocol toward greater functional-group tolerance paved the way for the preparation of various substituted corannulenes. [127] In an attempt to modularize the otherwise complex stepwise synthesis of carbon-rich molecular nanostructures, Diederich and co-workers pioneered [33,34] and recently reviewed [136] the field of "acetylenic scaffolding", in which a small and simple set of (E)-1,2-diethynylethene, 1,1,2,2tetraethynylethene, and related derivatives are used as building blocks for the construction of large carbon-rich molecules (Scheme 5). This approach resulted in impressive molecular structures such as a 17.8 nm long fully conjugated oligo(triacetylene), [137] an expanded octa(methoxy)cubane, [138] as well as a [6]radialene in which the perethynylated core adopted a nearly perfect chairlike conformation.…”

Nanostrukturierte Kohlenstoffmaterialien aus molekularen Vorstufen

“…[127] Diederich und Mitarbeiter versuchten die komplizierte mehrstufige Synthese molekularer Kohlenstoff-Nanostrukturen zu vereinfachen und begründeten damit das Gebiet der "acetylenischen Gerüste", [33,34] deren neueste Entwicklungen kürzlich in einem Übersichtsartikel zusammengefasst wurden. [136] Basierend auf einem Bausatz aus kleinen kohlenstoffreichen Molekülen, z. B.…”

Electron Donor-Acceptor Organic Polymers by “Click” Type Cycloaddition/Retroelectrocyclization Reaction

“…The first step of cycloaddition/retroelectrocyclization reaction involves the reaction of electron-rich alkynes activated by strong electron-donating groups (EDGs) with a strong electron-accepting cyanoolefinic molecule via a [2+2] cycloaddition to form the cyclobutene rings, and in the subsequent step, these cyclobutene rings are spontaneously opened to produce the donor-acceptor type chromophores in quantitative yields under mild conditions [12]. The currently available electron-donating groups for almost quantitative yields include aromatic amines [13][14][15][16], ferrocene [17,18], azulene, and organometallic derivatives [19,20]. Examples of electron-accepting cyanoolefinic molecules are tetracyanoethylene (TCNE), 7,7,8,8-tetracyanoquinodimethane (TCNQ ) and its derivatives [21][22][23][24], as well as dicyanovinyl and tricyanovinyl derivatives [25,26].…”