Synthesis, Structure, and Resolution of Exceptionally Twisted Pentacenes

Oligomers and Polymers Based on Pentacene Building Blocks

Functionalized pentacene derivatives continue to provide unique materials for organic semiconductor applications. Although oligomers and polymers based on pentacene building blocks remain quite rare, recent synthetic achievements have provided a number of examples with varied structural motifs. This review highlights recent work in this area and, when possible, contrasts the properties of defined-length pentacene oligomers to those of mono- and polymeric systems.

Synthesis of benzo[c] and naphtho[c]heterocycle diesters and dinitriles via homoelongation

Syntheses of benzo[c] and naphtho[c]heterocycle diesters and dinitriles were achieved via our newly developed iterative elongation protocol. The photophysical and electrochemical properties of these conjugated systems are explored.

X-ray structures of cyclophanes derived from naphtho[1,2-c:5,6-c]difuran and the synthesis, structure, and reaction kinetics of its 1,3,6,8-tetrasilylated derivative

A silylated derivative of naphtho[1,2-c:5,6-c]difuran, 1,3,6,8-tetrakis(tert-butyldimethylsilyl)naphtho[1,2-c:5,6-c]difuran, has been isolated and its X-ray crystal structure determined. Bond localization confirms the polyene character of this isobenzofuran ring system. This molecule undergoes two successive Diels-Alder reactions with second-order rate constants differing by over 2 orders of magnitude, consistent with predictions based on their structure-count ratios and with the reactivity of the novel 1,3-bis(tert-butyldimethylsilyl)isobenzofuran. Crystal structures of two cyclophanes derived from the reaction of naphtho[1,2-c:5,6-c]difuran and bis(imide) or bis(ester) dienophiles show marked differences in the conformation of the aliphatic chain found in the solid state.

An organometallic route to long helicenes

Along with the recent progress in the development of advanced synthetic methods, the chemical community has witnessed an increasing interest in promising carbon-rich materials. Among them, helicenes are unique 3D aromatic systems that are inherently chiral and attractive for asymmetric catalysis, chiral recognition and material science. However, there have been only limited attempts at synthesizing long helicenes, which represent challenging targets. Here, we report on an organometallic approach to the derivatives of undecacyclic helicene, which is based on intramolecular [2 + 2 + 2] cycloisomerization of aromatic hexaynes under metal catalysis closing 6 new cycles of a helicene backbone in a single operation. The preparation of nonracemic compounds relied on racemate resolution or diastereoselective synthesis supported by quantum chemical (density functional theory) calculations. The fully aromatic [11]helicene was studied in detail including the measurement and theoretical calculation of its racemization barrier and its organization on the InSb (001) surface by STM. This research provides a strategy for the synthesis of long helical aromatics that inherently comprise 2 possible channels for charge transport: Along a pi-conjugated pathway and across an intramolecularly pi-pi stacked aromatic scaffold.

1,3-diphenylisobenzofuran

The structure of the title compound, 1,3-diphenyl-2-benzofuran, C₂₀H₁₄O, exhibits a distinct alternation of short [mean 1.361 (3) Å] and long [mean 1.431 (3) Å] C—C bonds around the benzofuran ring system, indicating a predominantly polyene character. Over 60 Diels–Alder adducts of this commercially available furan have been structurally characterized, but this is the first report of the structure of the parent compound.