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Unveiling how intramolecular stacking modes of covalently linked dimers dictate photoswitching properties.

ABSTRACT: Covalently linked ?-stacked dimers represent the most significant platform for elucidating the relationship between molecular alignments and their properties. Here, we present the one-pot synthesis of two intramolecularly ?-stacked dimers and disclose how intramolecular stacking modes dictate photoswitching properties. The dimer, which features cofacially stacked chromophores and geometrically favours intramolecular photochemical [2?+?2] cycloadditions, displays a nearly irreversible photoswitching behaviour. By contrast, the dimer, bearing crosswise stacked chromophores, is geometrically unfavourable for the cycloaddition and exhibits a highly reversible photoswitching process, in which the homolysis and reformation of carbon-carbon single bonds are involved. Moreover, the chiral carbon centres of both dimers endow these photoswitches with chirality and the separated enantiomers exhibit tuneable chiroptical properties by photoswitching. This work reveals that intramolecular stacking modes significantly influence the photochemical properties of ?-stacked dimers and offers a design strategy toward chiral photoswitchable materials.

SUBMITTER: Lu RQ

PROVIDER: S-EPMC6889182 | biostudies-literature | 2019 Dec

REPOSITORIES: biostudies-literature

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Unveiling how intramolecular stacking modes of covalently linked dimers dictate photoswitching properties.

Lu Ru-Qiang RQ Yan Xiao-Yun XY Zhu Lei L Zhu Lei L Yang Lin-Lin LL Qu Hang H Wang Xin-Chang XC Luo Ming M Wang Yu Y Chen Rui R Wang Xiao-Ye XY Lan Yu Y Pei Jian J Weng Wengui W Xia Haiping H Cao Xiao-Yu XY

Nature communications 20191202 1

Covalently linked π-stacked dimers represent the most significant platform for elucidating the relationship between molecular alignments and their properties. Here, we present the one-pot synthesis of two intramolecularly π-stacked dimers and disclose how intramolecular stacking modes dictate photoswitching properties. The dimer, which features cofacially stacked chromophores and geometrically favours intramolecular photochemical [2 + 2] cycloadditions, displays a nearly irreversible photoswitch ...[more]

PMID: 31792204

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Project description:A versatile method is presented to form dendrimer superstructures by exploiting coacervate-core micelles as a template to confine and organize the hyperbranched macromolecules. First, complex coacervate-core micelles are formed from negative-neutral block copolymers and positively charged polyamidoamine dendrimers. The dendrimers inside the micellar core are then covalently cross-linked with each other upon addition of glutaraldehyde. After removal of the block copolymer from the assembly by increasing the salt concentration, consecutively, the formed Schiff bases cross-linking the dendrimers are reduced to amines, followed by a final dialysis step. This leads to well-defined covalently cross-linked nanostructures, coined dendroids, with a size of around 30 nm in diameter and a molecular weight of approximately 2.5 MDa. By incorporating dendrimer-encapsulated gold nanoparticles (AuDENs) into the micelle template strategy, the aggregation number of dendrimers inside the dendroids is determined by counting the nanoparticles in TEM micrographs. Furthermore, TEM performed at different tilt angles and AFM analysis corroborate formation of stable, covalently linked three-dimensional structures. Reconstruction of the TEM tilt series results in a tomogram further illustrating the 3D distribution of the gold nanoparticles, and hence the individual dendrimers, in the nanostructure. These dendroids appear to have a hard, poorly compressible core and a relatively soft outside. The versatility of the hierarchical building up of the supermolecules is illustrated by the controlled and synchronous incorporation of empty dendrimers and AuDENs into a single hybrid dendroid structure. The presented strategy allows for the preparation of a variety of classes of supermolecules, depending on the type of micellar-core macromolecule, e.g., dendrimer, cross-linker, and nanoparticles, used. Considering the broad interest in dendrimers as well as micelles in a plethora of research areas, e.g., (targeted) drug delivery, biomedical imaging, theragnostics, and catalysis, there is a great potential for dendroids and related classes of covalently linked macromolecules, viz., supermolecules.

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Unveiling how intramolecular stacking modes of covalently linked dimers dictate photoswitching properties.

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Unveiling how intramolecular stacking modes of covalently linked dimers dictate photoswitching properties.

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