Hierarchical Two‐Level Supramolecular Chirality of an Achiral Anthracene‐Based Tetracationic Nanotube in Water

Abstract

Herein, we report an achiral anthracene-based tetracationic nanotube (1•4Cl À ) that shows two levels of supramolecular chirality: namely, conformationally adaptive host-guest complexation with nucleoside triphosphates (e.g. ATP, GTP, CTP, and UTP) and twisted packing of the chiral host-guest complexes in water. Interestingly, achiral 1•4Cl À exhibits chiral recognition for ATP/GTP and CTP/UTP through structural transformation of its intramolecular Mand P-twisted conformation as the first level of supramolecular chirality, which leads to adaptive chirality with opposite CD responses. Furthermore, the formation of chiral M-1•4Cl À 'ATP can promote an intermolecular P-twisted dimeric packing of anthracene rings as the second level of supramolecular chirality to achieve assembled chirality with strong circularly polarized luminescence arising from the excimer ((+)-CPL, g lum % 10 À2 ) in water.

Chiral exciplex dyes showing circularly polarized luminescence: extension of the excimer chirality rule

“… 2 To develop CPL dyes, connecting two of the same aromatic luminophores, which can form an excimer (excited homodimer), to a chiral unit is one of the main approaches because these luminophores often emit with high quantum yields and large Stokes shifts. For example, CPL-active pyrene, 3,4 perylene, 4 b ,5 anthracene, 6 carbazole, 7 and naphthalimide 5 c ,8 excimers have been reported. In contrast, exciplex (excited heterodimer) CPL dyes are still rare, although exciplex fluorescence (FL) dyes are often used in the field of materials and biological sciences.…”

Hierarchical Two‐Level Supramolecular Chirality of an Achiral Anthracene‐Based Tetracationic Nanotube in Water

“…To further understand the relationship between the conformational structure and CD signals, a single crystal of 1•4Cl À 'GTP suitable for X-ray analysis was obtained by the evaporation of water (Figure 5). [10] The X-ray structure of 1•4Cl À 'GTP reveals that this chiral host-guest complex is stabilized by multiple noncovalent interactions, including C À 4) are seen between the pelectron-deficient anthracene rings and the guanine unit, which indicates that the cavity of 1•4Cl À matches well with the nucleobase units of nucleotides (Figure 5 b). It is worth noting that the three-center hydrogen bonds act as a driving force to successfully induce the conformation of 1•4Cl À from a symmetrical conformation to an M-twisted conformation, thereby resulting in shorter distances of 3.8-3.9 between the imidazolium CH groups compared with the 4.3 separation…”

“…The X-ray structure of 1•4Cl À confirms that the nanotube structure formed mainly by four imidazolium and four anthracene rings is achiral and has D 2h symmetry (Figure 2). [10] 1•4Cl À has a large hydrophobic cavity, where the CH sites of the imidazolium rings point to the inside of the cavity, with an average distance of 4.3 between two imidazolium rings (Figure 2 a). [11] The nanotube possesses a cuboid internal cavity with a size of approximately 12.1-(length) 7.7 (width) 7.3 3 (height), which is a suitable size for p-p interactions (Figure 2 a,b).…”

Circular Dichroism Based Chirality Sensing with Supramolecular Host–Guest Chemistry

“…An anthracene-based tetracationic cyclophane (25, Figure 10e) is able to work as a chirality sensor for nucleoside triphosphates in water. [63] Cyclo[6]aramide (26, Figure 10f) is reported to exhibit induced CD signals in the presence of L-amino acid esters in chloroform. [64] As discussed above, cucurbit[n]urils have excellent guest binding ability and thus a wide guest scope as a result of the hydrophobic effects originating from their well-defined and rigid cavities.…”