Described here is a three-component self-assembly system that displays emergent behavior that differs from that of its constituents. The system comprises an all-hydrocarbon octaaryl macrocycle cyclo[8](1,3-(4,6-dimethyl)benzene (D 4d -CDMB-8), corannulene (Cora), and I2. No appreciable interaction is seen between any pair of these three-components, either in cyclohexane or under various crystallization conditions. On the other hand, when all three-components are mixed in cyclohexane and allowed to undergo crystallization, a supramolecular iodine-containing capsule, ((D 4d -CDMB-8)3 ⊃(Cora)2)⊃I2, is obtained. This all-hydrocarbon capsule consists of three D 4d -CDMB-8 and two Cora subunits and contains a centrally bound I2 molecule as inferred from single-crystal and powder X-ray diffraction studies as well as solid-state 13C NMR and Raman spectroscopy. These analyses were complemented by solution-phase 1H NMR and UV–vis spectroscopic studies. No evidence of I2 escape from the capsule is seen, even at high temperatures (e.g., up to 418 K). The bound I2 is likewise protected from reaction with alkali or standard reductants in aqueous solution (e.g., saturated NaOH(aq) or aqueous Na2S2O3). It was also found that a mixed powder containing D 4d -CDMB-8 and Cora in a 3:2 molar ratio could capture saturated I2 vapor or iodine from aqueous sources (e.g., 1.0 mM I2 in NaCl (35 wt %) or I2 + NaI(aq) (1.0 mM each)). The present system displays structural and functional features that go beyond what would be expected on the basis of a simple sum-of-the-components analysis. As such, it illustrates a new approach to creating self-assembled ensembles with emergent features.
A novel chiral nanographene (i.e. EP9H) with a pentadecabenzo[9]helicene core fragment has been synthesized and fully characterized. Single‐crystal X‐ray diffraction unambiguously confirms the helical structure. The fluorescence emission of EP9H is located in the near infrared region (λem=684 nm) with a medium quantum yield (0.10) for helicene derivatives. Cyclic voltammetry reveals its seven quasi‐reversible redox states from −2 to +5. Furthermore, enantiopure EP9H displays distinct CD signals in a broad spectral range from 300 to 700 nm. Notably, compared to the reported small organic molecules, EP9H displays an outstanding |glum| value of 4.50×10−2 and BCPL as 304 M−1 cm−1.
Substituent effects play critical roles in both modulating reaction chemistry and supramolecular self-assembly processes. Using substituted terephthalate dianions (p-phthalic acid dianions; PTADAs), the effect of varying the type, number, and position of the substituents was explored in terms of their ability to regulate the inherent anion complexation features of a tetracationic macrocycle, cyclo[2](2,6-di(1H-imidazol-1-yl)pyridine)[2](1,4-dimethylenebenzene) (referred to as the Texas-sized molecular box; 1 4+), in the form of its tetrakis-PF6 – salt in DMSO. Several of the tested substituents, including 2-OH, 2,5-di(OH), 2,5-di(NH2), 2,5-di(Me), 2,5-di(Cl), 2,5-di(Br), and 2,5-di(I), were found to promote pseudorotaxane formation in contrast to what was seen for the parent PTADA system. Other derivatives of PTADA, including those with 2,3-di(OH), 2,6-di(OH), 2,5-di(OMe), 2,3,5,6-tetra(Cl), and 2,3,5,6-tetra(F) substituents, led only to so-called outside binding, where the anion interacts with 1 4+ on the outside of the macrocyclic cavity. The differing binding modes produced by the choice of PTADA derivative were found to regulate further supramolecular self-assembly when the reaction components included additional metal cations (M). Depending on the specific choice of PTADA derivatives and metal cations (M = Co2+, Ni2+, Zn2+, Cd2+, Gd3+, Nd3+, Eu3+, Sm3+, Tb3+), constructs involving one-dimensional polyrotaxanes, outside-type rotaxanated supramolecular organic frameworks (RSOFs), or two-dimensional metal–organic rotaxane frameworks (MORFs) could be stabilized. The presence and nature of the substituent were found to dictate which specific higher order self-assembled structure was obtained using a given cation. In the specific case of the 2,5-di(OH), 2,5-di(Cl), and 2,5-di(Br) PTADA derivatives and Eu3+, so-called MORFs with distinct fluorescence emission properties could be produced. The present work serves to illustrate how small changes in guest substitution patterns may be used to control structure well beyond the first interaction sphere.
A new approach to anion sensing that involves excimer disaggregation induced emission (EDIE) is reported. It involves the anion-mediated disaggregation of the excimer formed from a cationic macrocycle. This leads to an increase in the observed fluorescence intensity. The macrocycle in question, cyclo[1]N 2,N 6-dimethyl-N 2,N 6-bis(6-(1H-imidazolium-1-yl)pyridin-2-yl)pyridine-2,6-diamine[1]1,4-dimethylbenzene (1 2+; prepared as its PF6 – salt), is obtained in ca. 70% yield via a simple cyclization. X-ray diffraction analyses of single crystals revealed that, as prepared, this macrocycle exists in a supramolecular polymeric form in the solid state. Macrocycle 1 2+ is weakly fluorescent in acetonitrile. The emission intensity is concentration dependent, with the maximum intensity being observed at [1 2+] ≈ 0.020 mM. This finding is ascribed to formation of an excimer, followed possibly by higher order aggregates as the concentration of 1 2+ is increased. Addition of tetrabutylammonium pyrophosphate (HP2O7 3–) to 1 2+ (0.020 mM in acetonitrile) produces a ca. 200-fold enhancement in the emission intensity (λex = 334 nm; λem = 390–650 nm). These findings are rationalized in terms of the HP2O7 3– serving to break up essentially non-fluorescent excited-state dimers of 1 2+ through formation of a highly fluorescent anion-bound monomeric complex, 1 2+·HP2O7 3–. A turn-on in the fluorescence intensity is also seen for H2PO4 – and, to a lesser extent, HCO3 –. Little (HSO4 –, NO3 –) or essentially no (N3 –, SCN–, F–, Cl–, Br– and I–) response is seen for other anions. Solid-state structural analysis of single crystals obtained after treating 1 2+ with HP2O7 3– in the presence of water revealed a salt form wherein a H2P2O7 2– anion sits above the cone-like macrocycle.
Solid‐state fluorescent materials play a critical role in the manufacture of light‐emitting diodes, laser dyes, storage materials, and fluorescence sensors. However, it remains challenging to produce solid‐state fluorescent materials using traditional organic dyes since most are subject to aggregation‐caused quenching (ACQ) in the solid state. Here, a macrocycle‐derived crystalline framework is reported that captures various cationic test‐ACQ dyes (e.g., Basic Red 2 (BR2)) and stabilizes them in a fluorescent form. Cyclo[3](1,3‐benzene)[3](4,6‐benzene)(1,3‐dicarboxylic acid), CA‐3, is used as the core macrocyclic building block. When allowed to coordinate with Zn(NO3)2•6H2O or Cd(NO3)2•4H2O, crystalline sponge (CS‐Zn or CS‐Cd) is obtained. In the case of CS‐Zn, nano‐sized cavities are observed in the solid state that serve as containers to capture the cationic ACQ dye BR2 with loading yields up to 14.6 wt% and emission enhancements up to 41× of those seen for solid BR2. The resulting dye‐containing material, CS‐Zn@BR2, displays high stability in water or selected organic solvents at room temperature or under reflux, or when heated at 300 °C for 1 h open to the air, or in the presence of sodium hypochlorite solution (3.0 mm). This study highlights a new strategy for rendering fluorescent ACQ dyes in the solid state.
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