Mechanoresponsive polymers hold great technological potential in drug delivery, 'smart' optical systems and microelectromechanical systems. However, hysteresis and fatigue (associated with large-scale polymer chain rearrangement) are often problematic. Here, we describe a polyarylamide film that contains s-dibenzocyclooctadiene (DBCOD), which can generate unconventional and completely reversible thermal contraction under low-energy stimulation. The films exhibit a giant negative thermal expansion coefficient of approximately -1,200 ppm K(-1) at ambient or near-ambient temperatures, much higher than any known negative-thermal-expansion materials under similar operating conditions. Mechanical characterization, calorimetry, spectroscopic analysis and density-functional theory calculations all point to the conformational change of the DBCOD moiety, from the thermodynamic global energy minimum (twist-boat) to a local minimum (chair), as the origin of this abnormal thermal shrinkage. This newly identified, low-energy-driven, thermally agile molecular subunit opens a new pathway to creating near-infrared-based macromolecular switches and motors, and for ambient thermal energy storage and conversion.

Large negative thermal expansion of a polymer driven by a submolecular conformational change.

Molecular Clips and Tweezers with Corannulene Pincers

A highly enantioselective method for the synthesis of 4-alkyl substituted 1,2,3,4-tetrahydroisoquinolines is reported The key step relies on the asymmetric synthesis of α-alkylarylacetic acids by alkylation of their corresponding amides employing (S,S)-(+)-pseudoephedrine as chiral inductor Subsequent Friedel−Crafts acylation, stereocontrolled reductive amination and Pictet−Spengler cyclization affords the title compounds in excellent yields and enantioselectivities

A New General Method for the Asymmetric Synthesis of 4-Alkyl-3-aryl-1,2,3,4-tetrahydroisoquinolines.

It is uncommon for a solid substance to expand upon cooling and contract upon heating. In this work, we synthesized a carbocycle monomer that contains 1,2:5,6-dibenzocyclooctadiene (DBCOD) unit and...

Design and Synthesis of Thermal Contracting Polymer with Unique Eight-Membered Carbocycle Unit

The crystal structures of 1,2;5,6-dibenzoocta-1,5-diene (1)(C16H16, P21/n A= 6.638, B= 6.892, C= 12.625 A, α= 90.00°, β= 96.58°, γ= 90.00°, Z= 2); 6,7,13,14-tetrahydrodipyrido[1,2-a:1,2-e]diazocinium dibromide (11)(C14H16N2Br2·2H2O, P21/n, A= 14.586, B= 6.146, C= 9.159 A, α= 90.00°, β= 104.16°, γ= 90.00°, Z= 2); 1,2;5,6;9,10-tribenzododeca-1,5,9-triene (12)(C24H24, P21/n, A= 19.140, B= 5.122, C= 19.214 A, α= 90.00°, β= 107.12°, γ= 90.00°, Z= 4) and 1,2;5,6;9,10;13,14-tetrabenzohexadeca-1,5,9,13-tetraene (16)(C32H32, P21, A= 12.560, B= 33.665, C= 11.312 A, α= 90.00°, β= 90.38°, γ= 90.00°, Z= 8) have been determined. The first two, which belong to the 6,8,6 ring system, exist in the solid state in the chair conformation, whereas both the chair and the boat forms are present in solution. The central twelve-membered ring of compound 12 exists in the crystal as an almost perfect C2 propeller, which is also the only observed conformation in solution. Finally, there are four different molecules of compound 16 in the crystal; however, they roughly correspond to the same conformation (and its enantiomer)[(+–+,–+–,++–,–––) and (–+–,+–+,––+,+++)]. Partial and complementary to literature NMR (1H and 13C) results agree with previous conformational analyses in solution.

https://repositorioinstitucional.ceu.es/bitstream/10637/5520/1/Molecular_Domiano_J_Chem_Soc_Perkin_Trans_1992.pdf

The molecular structure of 6, 8, 6 and related systems

Conformational analysis of 1,2:5,6:9,10-tribenzocyclododeca-1,5,9-triene by proton NMR at 173 K

The Molecular Structure of 6, 8, 6 and Related Systems.

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The molecular structure of 6, 8, 6 and related systems

Conformational analysis of 1,2:5,6:9,10-tribenzocyclododeca-1,5,9-triene by proton NMR at 173 K

The Molecular Structure of 6, 8, 6 and Related Systems.