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Stimuli-controlled self-assembly of diverse tubular aggregates from one single small monomer.

ABSTRACT: The design and synthesis of new stimuli-responsive hydrogen-bonding monomers that display a diversity of self-assembly pathways is of central importance in supramolecular chemistry. Here we describe the aggregation properties of a simple, intrinsically C₂-symmetric enantiopure bicyclic cavity compound bearing a terminally unsubstituted ureidopyrimidinone fragment fused with a pyrrole moiety in different solvents and in the absence and presence of C₆₀ and C₇₀ guests. The tetrameric cyclic aggregate is selectively obtained in chlorinated solvents, where only part of the available hydrogen bonding sites are utilized, whereas in toluene or upon addition of C₇₀ guests, further aggregation into tubular supramolecular polymers is achieved. The open-end cyclic assemblies rearrange into a closed-shell capsule upon introduction of C₆₀ with an accompanied symmetry breaking of the monomer. Our study demonstrates that a C₆₀ switch can be used to simultaneously control the topology and occupancy of tubular assemblies resulting from the aggregation of small monomers.

SUBMITTER: Shi Q

PROVIDER: S-EPMC5394284 | biostudies-literature | 2017 Apr

REPOSITORIES: biostudies-literature

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Stimuli-controlled self-assembly of diverse tubular aggregates from one single small monomer.

Shi Qixun Q Javorskis Tomas T Bergquist Karl-Erik KE Ulčinas Artūras A Niaura Gediminas G Matulaitienė Ieva I Orentas Edvinas E Wärnmark Kenneth K

Nature communications 20170412

The design and synthesis of new stimuli-responsive hydrogen-bonding monomers that display a diversity of self-assembly pathways is of central importance in supramolecular chemistry. Here we describe the aggregation properties of a simple, intrinsically C2-symmetric enantiopure bicyclic cavity compound bearing a terminally unsubstituted ureidopyrimidinone fragment fused with a pyrrole moiety in different solvents and in the absence and presence of C60 and C70 gues ...[more]

PMID: 28401927

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Project description:A bis(squaraine) dye equipped with alkyl and oligoethyleneglycol chains was synthesized by connecting two dicyanomethylene substituted squaraine dyes with a phenylene spacer unit. The aggregation behavior of this bis(squaraine) was investigated in non-polar toluene/tetrachloroethane (98:2) solvent mixture, which revealed competing cooperative self-assembly pathways into two supramolecular polymorphs with entirely different packing structures and UV/Vis/NIR absorption properties. The self-assembly pathway can be controlled by the cooling rate from a heated solution of the monomers. For both polymorphs, quasi-equilibrium conditions between monomers and the respective aggregates can be established to derive thermodynamic parameters and insights into the self-assembly mechanisms. AFM measurements revealed a nanosheet structure with a height of 2 nm for the thermodynamically more stable polymorph and a tubular nanorod structure with a helical pitch of 13 nm and a diameter of 5 nm for the kinetically favored polymorph. Together with wide angle X-ray scattering measurements, packing models were derived: the thermodynamic polymorph consists of brick-work type nanosheets that exhibit red-shifted absorption bands as typical for J-aggregates, while the nanorod polymorph consists of eight supramolecular polymer strands of the bis(squaraine) intertwined to form a chimney-type tubular structure. The absorption of this aggregate covers a large spectral range from 550 to 875 nm, which cannot be rationalized by the conventional exciton theory. By applying the Essential States Model and considering intermolecular charge transfer, the aggregate spectrum was adequately reproduced, revealing that the broad absorption spectrum is due to pronounced donor-acceptor overlap within the bis(squaraine) nanorods. The latter is also responsible for the pronounced bathochromic shift observed for the nanosheet structure as a result of the slip-stacked arranged squaraine chromophores.

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Stimuli-controlled self-assembly of diverse tubular aggregates from one single small monomer.

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Stimuli-controlled self-assembly of diverse tubular aggregates from one single small monomer.

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