Abstract
A couple of water-soluble chiral 2,6-helic[6]arene derivatives P-H1 and M-H1 were synthesized, and they could form 1:1 stable complexes with 4-[(4′-N, N-diphenylamino)-styryl]-N-methylpyridinium iodide (G) in water. Compared with G, the host-guest complexes exhibited enhanced fluorescence, which might be attributed to the spatial confinement of G and restriction of aggregation-caused quenching (ACQ) effects. Based on the host-guest complexation, the first helic[6]arene-based chiral assemblies were then constructed, and they showed rectangular or hexagonal nanostructures by scanning electron microscopy (SEM) images. Interestingly, the assemblies showed clear mirror-image circular dichroism (CD) and circularly polarized luminescence (CPL) spectra in aqueous solution, revealing a consecutive chirality transfer from the chiral macrocyclic cavities of the hosts to G. Moreover, the supramolecular chirality of the assemblies could also show responsiveness to the pH values and temperatures of the system.
Highlights
Polarized luminescent (CPL) materials have aroused extensively interest for their potential applications in the fields of biological probes (Carr et al, 2012), photoelectric devices (Grell et al, 2001; Shimada et al, 2017; Li et al, 2018a), asymmetric synthesis (Kawasaki et al, 2005; Xu et al, 2014), and chiral sensing (Yang et al, 2013)
As shown in Scheme 1, treatment of P-H4 and methyl bromoacetate in acetonitrile in the presence of K2CO3 provided methoxycarbonyl-substituted 2,6-helic[6]arene P-H3 in 93% yield, which were followed by the hydrolysis with sodium hydroxide aqueous solution and acidification with hydrochloric acid to give the 2,6-helic[6]arene derivative P-H2
From the 2D ROESY spectrum of a solution of 2.0 mM P-H1 and 2.0 mM G (Figures S10, S11), correlations were observed between protons H2, H3 of guest G and protons Ha on P-H1, which further indicated that in the complex, the methylpyridinium group of G was located inside the cavity of P-H1, while the benzene ring connected with the double bond of G might be located outside the cavity
Summary
Polarized luminescent (CPL) materials have aroused extensively interest for their potential applications in the fields of biological probes (Carr et al, 2012), photoelectric devices (Grell et al, 2001; Shimada et al, 2017; Li et al, 2018a), asymmetric synthesis (Kawasaki et al, 2005; Xu et al, 2014), and chiral sensing (Yang et al, 2013). It was further deduced that chiral macrocyclic arenes could provide an opportunity to develop the CPL materials based on the host-guest complexation. Based on the host-guest complexation, the first helic[6]arene-based chiral assemblies with rectangular or hexagonal nanostructures were constructed.
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