Functional acetylenic molecular architecture

Abstract

A diversity of perethynylated building blocks, in particular derivatives of tetraethynylethene (TEE, 3,4-diethynylhex-3-ene-1,5-diyne), were prepared for the construction of multinanometer-sized functional molecular objects. Macrocyclic acetylenic scaffolding yielded perethynylated antiaromatic octadehydro [12]annulenes and aromatic dodecadehydro [18]annulenes as well as highly stable expanded radialenes with extended all-carbon cores. An attempted new synthesis of perethynylated octadehydro [12]annulenes was unsuccessful and led to the isolation of a highly strained permethylenated cycloocta-1,5-diyne instead. Acyclic acetylenic scaffolding using both TEEs and 1,2-diethynylethenes (DEEs (E)-hex-3-ene-1,5-diynes) afforded the first oligomers and polymers with the poly(triacetylene) backbone [PTA, -(CϵC-CR¼CR-CϵC) n -]. The effective conjugation length for this third class of linearly conjugated polymers with a nonaromatic all-carbon backbone, besides polyacetylene and poly(diacetylene), was determined to be in the range of 7-10 monomeric units. By lateral attachment of dendrons along the conjugated backbone of PTA oligomers, cylindrically shaped dendrimers were obtained which can be viewed as insulated molecular wires. Donoracceptor substituted arylated TEEs and DEEs were prepared, and their unusual electrochemical properties and tendency to undergo photochemical trans → cis isomerization were investigated. Measurements of third-order nonlinear optical effects by third harmonic generation revealed useful structure-function relationships. The highest second hyperpolarizabilities ␥ were obtained for two-dimensionally fully conjugated systems with reduced molecular symmetry. PERETHYNYLATED BUILDING BLOCKS FOR MODULAR CHEMISTRYAcetylenic molecular scaffolding in one, two, and three dimensions aims at producing new nanoscale molecular and polymeric materials that exhibit unusual electronic and optical function and properties. These efforts have greatly benefited from the recent renaissance in preparative acetylene chemistry [1] and, in particular, from the discovery of novel metal-catalyzed cross-coupling reactions for C-C bond formation [2]. A rich variety of peralkynylated building blocks have been prepared as starting materials in this modular synthetic approach to new advanced materials [3][4][5][6] and, among these, derivatives of tetraethynylethene (1, TEE, 3,4-diethynylhex-3-ene-1,5-diyne) [7][8][9] are particularly useful. Today, TEEs of nearly any desired functionalization and silyl-protection are available. Additional perethynylated chromophores such as the [3]radialene 2 [10] and [3]cumulene 3 [11] have been prepared in our laboratory. On the other hand, all efforts to synthesize the perethynylated allene 4, a precursor to threedimensional networks and for formation of helical polymers, have failed in the past [12] (Scheme 1). MACROCYCLIC ACETYLENIC SCAFFOLDINGOxidative Glaser-Hay macrocyclization of cis-bis(trialkylsilyl)-protected TEEs yielded the per(silylethynyl)ated octadehydro [12]annulenes...

Insulated Molecular Wires: Dendritic Encapsulation of Poly(triacetylene) Oligomers, Attempted Dendritic Stabilization of Novel Poly(pentaacetylene) Oligomers, and an Organometallic Approach to Dendritic Rods

“…An interesting observation was made during purification of the end-capped thirdgeneration monomer 3a by preparative GPC [28]. Instead of the expected single resonance, two t-Bu resonances were observed in the 1 H-NMR spectrum and TLC of the solution showed two spots.…”

François Diederich (1952–2020): 40 Jahre Organische Chemie

“…Mit Hilfe der Acetylen‐Kupplungschemie [37] (z. B. Glaser/Eglinton/Hay‐ oder Sonogashira‐Kupplungen) wurden acetylenhaltige Monomere zu linearen (“molekulare Drähte”), cyclischen oder verzweigten, z. T. dendritischen Oligomeren mit definierter Struktur verknüpft [34] . Sie wurden vielfach mit Elektronendonoren und ‐akzeptoren ausgestattet, was interessante optoelektronische Eigenschaften mit intensiven Charge‐Transfer‐Banden lieferte [38–40] .…”

“…[20] All diese Arbeiten weckten das Interesse,w eitere bis dato unbekannte Kohlenstoffallotrope oder kohlenstoffreiche Moleküle herzustellen. [33] Systematisch wurden dazu in den Diederich-Laboren durch so genanntes "acetylenic scaffolding" Bausteine mit Doppel-und Dreifachbindungen zu neuen Molekülen mit zwei-oder dreidimensionalem Kohlenstoffgerüst verknüpft (Abbildung 2C), [34][35][36] z. B. zu expandierten Radialenen (Abbildung 2C).…”

Third harmonic generation via dendrimers of four generations

“…Investigation of first generation of resorcinarene dendrimers showed an increase of cubic nonlinear susceptibility by about a factor of five, when phenyl ended group was substituted by a ferrocenyl group [1]. Measurements of third-order nonlinear optical effects by THG revealed useful structure-function relationships in cylindrically shaped dendrimers [2]. Moreover, THG via dendrimers has been successfully employed for monitoring laser induced optical effects in the material [3].…”