Programmed Synthesis of Molecular Wires with Fixed Insulation and Defined Length Based on Oligo(phenylene ethynylene) and Permethylated α‐Cyclodextrins

Abstract

The development of new tuning methods for π-conjugated insulated molecular wires with strictly defined axle lengths as well as positions and degrees of macrocycle coverage would provide unprecedented insight into insulation effects in functionalized materials. Herein, iterative reactions of oligo(phenylene ethynylene) (OPE) linked with permethylated α-cyclodextrins were carried out to fabricate insulated molecular wires with a defined length and insulation in desired areas. Insulated OPEs were elongated in a stepwise manner by performing sequential coupling/deprotection reactions. The insulated areas on the OPE units in each expansion step were selectively controlled by means of programmed solvent conditions (high/low polarity). Moreover, a completely insulated OPE (up to a linked [11]rotaxane) with high structural regularity and high covering ratio was synthesized by appropriate tuning of the Pd catalyst and an extension unit bearing a traceless capping unit based on a tert-butyldimethylsilyl group. This strategy may guide the development of the selective synthesis of fully insulated, partially insulated, and uninsulated molecular wires with well-defined lengths and covered/uncovered areas.

Synthetic Methodology for Structurally Defined and Insulated Molecular Wires Bearing Non‐centrosymmetric Conjugated Axle Components via Iterative Intramolecular Slippage

“…In this system, the product was kinetically trapped after cooling and transferring to a non‐polar solvent, hence cross‐coupling reactions in aqueous media were not necessary (Figure a, bottom) . The technique in Figure a top was applied to a programmed synthesis via an iterative procedure (Figure b) . The method afforded precise molecular engineering of IMWs bearing desired conjugation length and controlled molecular interactions, which are the critical factors for materials used in molecular electronics and sensors …”

“…The previously reported programmed methodology was limited to centrosymmetric conjugated axle structures and involved specialized reaction conditions . The iterative reactions needed aqueous media and a water‐soluble palladium catalyst in order to fix the supramolecular structures; the protocol had strong limitations and the coupling components without aqueous solubility could not be utilized to obtain diverse π‐conjugated systems.…”

“…[20,21] The previously reported programmedm ethodology was limited to centrosymmetric conjugated axle structures and involveds pecialized reaction conditions. [19] The iterative reactions needed aqueous mediaa nd aw ater-soluble palladium catalyst [22] in order to fix the supramolecular structures;t he protocolh ad strong limitations and the coupling components without aqueous solubility could not be utilized to obtain diverse p-conjugated systems. Moreover,a sc ompared to their centrosymmetric conjugation counterparts, non-centrosymmetric conjugated systemsa re being pursued more eagerly for their applicationsi ntransportation of materials, energies,a nd electrons in the fields of biomaterials, molecular machines, and molecular electronics.…”

“…[18] The technique in Figure 1a top was applied to ap rogrammeds ynthesis via an iterative procedure ( Figure 1b). [19] The methoda fforded precise molecular engineering of IMWs bearing desired conjugation length and controlled molecular interactions, which are the criticalf actors for materials used in molecular electronics and sensors. [20,21] The previously reported programmedm ethodology was limited to centrosymmetric conjugated axle structures and involveds pecialized reaction conditions.…”

“…Moreover,a sc ompared to their centrosymmetric conjugation counterparts, non-centrosymmetric conjugated systemsa re being pursued more eagerly for their applicationsi ntransportation of materials, energies,a nd electrons in the fields of biomaterials, molecular machines, and molecular electronics. [23] Herein, af acile and programmable synthetic methodology for IMWs bearing non-centrosymmetric conjugated axle components, possessing different groups at the ends of the non-centrosymmetricc onjugated backbone, is reported,w hich could serve as ap latform to generate materials for the above-mentioned applications.T his methodi sa fusion of two strategies-the intramoleculars lippage transformation [18] and the iterative cross-coupling reaction, [19] in which kinetically stable IMWs could be prepared without requiring coupling reactions in aqueous media. The newly programmed synthetic methodology for IMWs bearing non-centrosymmetric conjugated axle components,a ss hown in Figure 1c,i nvolves general cross-coupling reactions in common organic solvents followed by intramolecular slippage isomerizationi na queous media, thereby assisting in overcoming the structural limitations posed by earlier methods.…”