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Synthesis 2025; 57(14): 2189-2196
DOI: 10.1055/a-2593-4590
paper
Romanian Chemists in Synthesis

Azulene-Based Organic Cages Formed with 1,3,5-Tris(aminomethyl)-2,4,6-triethylbenzene: Synthesis and Physicochemical Properties

Adrian E. Ion
a   C. D. Nenitzescu Institute of Organic and Supramolecular Chemistry, Splaiul Independentei 202B, 060023 Bucharest, Romania
,
Andreea Dogaru
a   C. D. Nenitzescu Institute of Organic and Supramolecular Chemistry, Splaiul Independentei 202B, 060023 Bucharest, Romania
,
Catalin Maxim
a   C. D. Nenitzescu Institute of Organic and Supramolecular Chemistry, Splaiul Independentei 202B, 060023 Bucharest, Romania
b   Faculty of Chemistry, University of Bucharest, Regina Elisabeta Blvd. 4–12, 030018 Bucharest, Romania
,
Anamaria Hanganu
a   C. D. Nenitzescu Institute of Organic and Supramolecular Chemistry, Splaiul Independentei 202B, 060023 Bucharest, Romania
b   Faculty of Chemistry, University of Bucharest, Regina Elisabeta Blvd. 4–12, 030018 Bucharest, Romania
,
Cristian Enache
c   National Phytosanitary Authority of Agriculture Ministery, Blvd. Voluntari 11, 077190 Voluntari, Ilfov, Romania
,
Marius Andruh∗
a   C. D. Nenitzescu Institute of Organic and Supramolecular Chemistry, Splaiul Independentei 202B, 060023 Bucharest, Romania
b   Faculty of Chemistry, University of Bucharest, Regina Elisabeta Blvd. 4–12, 030018 Bucharest, Romania
,
Simona Nica∗
a   C. D. Nenitzescu Institute of Organic and Supramolecular Chemistry, Splaiul Independentei 202B, 060023 Bucharest, Romania
› Author Affiliations

This work was supported by a grant from the Ministry of Research, Innovation and Digitization, CNCS-UEFISCDI, project number PN-IV-P8-8.3-ROMD-2023-0045, within PNCDI IV.
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This paper is dedicated to the memory of Professor Ovidiu Maior, an example of scientific excellence and mentorship.

Abstract

A novel [2+3] imine cage, derived from 1,3-diformylazulene and 1,3,5-tris(aminomethyl)-2,4,6-triethylbenzene, was synthesized and characterized. NMR spectroscopy and single crystal X-ray diffraction confirmed the formation of a symmetric hexaimine structure. The cage exhibits fluorescence, as well as characteristic azulene redox behavior. However, its stability in solution is sensitive to the acidity of the solvent. Reduction with NaBH4 led to the isolation of a more stable hexaamine cage, providing a means to further stabilize the structure.


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Key words

azulene-based cages - Schiff base - fluorescence - redox active - hexaamine macrocycle

Organic cages have emerged as a promising class of molecular materials with potential applications in gas storage, molecular recognition, and catalysis.[1] These compounds are discrete molecular architectures formed through the self-assembly of organic building blocks via covalent interactions.[2] Organic cages are often rigid molecules that retain their shape in both solid and solution states.[3] Notably, these cage molecules possess an intrinsic cavity and, upon assembly, an intercage porosity, exhibiting exceptional surface area and porosity.[4] In addition, their solution processability confers superior characteristics, surpassing those of conventional porous frameworks (e.g., MOFs, COFs, HOFs).[5] The synthesis of this family of compounds is based upon the formation of either irreversible or reversible chemical bond formation in one-pot reactions.[1] [2] The most effective approach employs Schiff base condensation reaction of amines and aldehydes, with ease of purification of the organic molecular cage.[6] Strategic functional group selection enables good control over the cavity size and shape of the resulting structure.[7] Additionally, rationally functionalized trigonal organic cages can serve as nodes for the construction of covalent organic frameworks, when reacting the functionalized cage with appropriate linear linkers.[8]

Among the various scaffolds used for organic cage synthesis, 1,3,5-tris(aminomethyl)-2,4,6-triethylbenzene (TAMTMB) is particularly appealing due to its rigid, threefold symmetric core.[9] The presence of amine groups at the 1,3,5 positions allows for diverse synthetic modifications, including imine bond formation.[10] The triethyl substituents at the 2,4,6 positions further enhance its structural stability by reducing conformational flexibility and steric hindrance during cage formation. TAMTMB forms three-dimensional organic cages with defined nanoscale cavities when reacted with tri- or dialdehydes.[11] These organic cages exhibit high surface areas and can be tailored for gas storage, separation, or drug delivery.[12]

Recently, we reported the synthesis of azulene-based cages using the reaction between azulene-1,3-dicarboxaldehyde and tris(2-aminoethyl)amine (TREN).[13] This flexible tertiary amine core allowed isolation of a cationic [1+1]2+ tetraimine cage and [2+3] hexaimine cage, through the control of the molar ratio and of the reaction conditions. In the case of the hexaimine cage, a conformational arrangement was observed in solution owing to flexible, aliphatic arms of TREN. These were advantageous for encapsulation of silver ions within the bistren cage. The packing of these molecules in the crystal leads to supramolecular architecture displaying a honeycomb topology. These encouraging results have motivated us to synthesize analogous cages with TAMTMB, a benzene-based core as a scaffold.

We report herein the synthesis of a hexaimine cage through Schiff base condensation of azulene-1,3-dicarboxaldehyde and 1,3,5-tris(aminomethyl)-2,4,6-triethylbenzene, and its subsequent conversion to a hexamine macrobicycle via sodium borohydride reduction. The fluorescent and redox properties of these cages are presented.

The reaction of 1,3,5-tris(aminomethyl)-2,4,6-triethylbenzene with azulene-1,3-dicarboxaldehyde in a 2:3 ratio yielded the hexaimine cage 1 (Scheme [1]). The cage is isolated as pure green precipitate from the reaction mixture.

Zoom Image
Scheme 1 Schematic representation of the cages synthesis

The IR spectrum of 1 shows strong C=N stretching vibration at 1620 cm–1 proving the existence of imine bonds. The structure was established by NMR spectroscopy and high-resolution mass spectrometry analysis. The ESI mass spectrometry gave an m/z peak at 943.54294 for [M + H]+, matching the expected molecular formula of C66H66N6 (calcd 943.54217). The cage exhibits poor solubility in methanol and is insoluble in DMSO or DMF. In contrast, it displays good solubility in chloroform and dichloromethane, allowing for the NMR characterization in CDCl3. However, we observed that the cage undergoes rapid hydrolysis in a slightly acidic deuterated solvent within a timeframe required for recording the 13C NMR spectrum. Thus, the characterization was performed in CDCl3 kept upon silver foil. In this case, the NMR spectra are consistent with the proposed hexaimine cryptand cage (Figure [1]). Cage 1 displays a fairly symmetric structure in solution with equivalent resonances of the three azulene units observed as four peaks at δ = 7.56 to 10.13. A signal corresponding to the six CH=N imine protons was observed at 8.18 ppm. Furthermore, a doublet signal at 5.23 ppm assigned to CH2N protons is consistent with the symmetric structure. The peaks at 3.42 ppm and 1.30 ppm are related to the CH2CH3 groups of the ethyl arm of the aromatic triamine.

Zoom Image
Figure 1 1H NMR spectrum of cryptand 1 recorded in CDCl3 at 298 K

In the 13C NMR spectrum of 1 [Figure S1, Supporting Information (SI)], twelve independent peaks are observed that are consistent with the expected cage structure, providing convincing evidence for its successful synthesis. In this spectrum, the peaks at 23.7 and 16.3 ppm are assigned to the CH2 and CH3 species of the ethyl group. The peak at 54.4 ppm is related to the carbon bonded to nitrogen and the peaks of aromatic carbons together with imine carbon are observed as six peaks in the range of 155.2–124.0 ppm. Under these conditions, the cage is stable both at high and low temperatures as confirmed by temperature-dependent 1H NMR spectroscopy (Figure S2, SI).

Further confirmation of this structure was provided by X-ray diffraction analysis. Single crystals were isolated from the reaction filtrate, by slow evaporation at room temperature. Cage 1 crystallizes as green rhombic crystals, in the P121/n1 space group. The two phenyl units of the 1,3,5-tris(aminomethyl)-2,4,6-triethylbenzene linker form the ‘floor’ and ‘roof’ of the central cavity, analogous to similar cages formed with phenylene- or pyrrole-based dicarboxaldehydes.[10c] [14] A perspective view of the molecular structure including atom labeling is depicted in Figure [2] and Figure S3 (SI), while Table [1] provides the summary of the crystallographic data together with refinement details. The imine groups are arranged on the same side of the phenyl ring, whereas the ethyl groups are oriented to the opposite side, outside the cavity. The inner dimension of the cavity, measured between the phenyl groups, is approximately 9.8 Å (calculated by the centroid-centroid distance). Inside the molecular cages, the bisimine units are arranged in anti,anti conformation, the cage showing an eclipsed conformation, propeller-like, feature also observed for the reported azulene-based bistren cage.[13]

Zoom Image
Figure 2 a) The asymmetric unit of cryptand 1 with atom labeling; b) top view of the propeller-like feature.

Table 1 Crystallographic Data for Cage 1

Empirical formula

C66H66N6

Fw

943.24

T [K]

293(2)

space group

P 1 21/n 1

a [Å]

14.0542(6)

b [Å]

16.4159(7)

c [Å]

26.2565(13)

a [°]

90

b [°]

93.649(4)

g [°]

90

V [Å3]

6045.4(5)

Z

4

ρ calcd [g cm–3]

1.036

μ [mm–1]

0.061

2Θ range

3.97 to 49

Reflections collected

37846

Data/restraints/parameters

9994/0/655

[Rint = 0.0566]

R1

0.0737

wR2

0.2055

GOF

1.028

Largest diff. peak/hole/eÅ–3

0.894/–0.226

The crystal packing of 1 is dominated by π-π interactions between the azulene moieties, which form columns running along the crystallographic b axis (Figure [3a] and Figure S4, SI). These interactions occur between the five-membered rings of azulene moieties within 3.58–3.64 Å range, measured as centroid-centroid distance, giving rise to one-dimensional supramolecular assemblies (Figure [3b]). Furthermore, the orientation of the ethyl groups facilitates C–H···π interactions (3.72 Å) between adjacent cage molecules, connecting the π-stacked columns into a bidimensional architecture (Figure [3c]).

Zoom Image
Figure 3 Packing diagram in crystal 1: a) columns running along the crystallographic b axis; b) one dimensional supramolecular assembly formed by π-π stacked azulene moieties; c) two-dimensional architecture formed by π-π and C–H∙∙∙π interactions.

In comparison with our previously described silver cryptate, the estimated voids volume by Olex2.-1.5 software is smaller, 1236 Å3 per unit cell and 360 electrons.[13]

Reduction of cage 1 with NaBH4 gave the corresponding macrobicyclic hexaamine 2 in almost quantitative yield. In contrast to 1, compound 2 is freely soluble in lipophilic solvents. The MS spectroscopy revealed the [M + H]+ molar peak at m/z 947.57353, which corresponds to the calculated value of 947.57347 for C66H70N6. The identity of this hexamine cage was confirmed by NMR spectroscopy (Figure [4]), also in CDCl3. The azulene signals are shifted upfield, except the proton at the 2 position, which is deshielded from 7.56 ppm in the hexaimine cage to 8.01 ppm in the corresponding hexaamine 2. The disappearance of the CH=N resonance and the appearance of a new set of signals at 4.39 and 3.96 ppm for CH2NH protons are in agreement with the formation of amine structure. The 13C NMR spectrum also testifies the formation of the hexaamine macrocyclic structure (Figure S3, SI). Two signals at 48.64 and 48.30 ppm corresponding to the NHCH2 groups confirm the formation of the amine type cage.

Zoom Image
Figure 4 1H NMR spectrum of hexaamine cryptand 2 recorded in CDCl3 at 298 K

The optical properties of both cages were investigated in CHCl3 by UV/vis absorption spectroscopy. The UV/vis spectrum of 1 as freshly prepared solution is shown in Figure [5a]. Cage 1 exhibits absorption features related to the conjugated system involving azulene moieties. Azulene derivatives typically show absorption in the visible region, which is often in the range of 400–500 nm due to S0-S1 transition.[15] The absorption spectrum of 1 shows two peaks in the UV region at 244 and 290 nm attributed to π→π* transitions of the aromatic ring, while the latter peak can be assigned to an S0→S2 transition of azulene.[13] [16] Relative broad absorption bands in the visible region are detected at 406 and 425 nm, characteristic of azulene S0-S1 transition. Azulene is a fluorescent compound that violates Kasha’s rule, emitting fluorescence from the S2 state.[17] Thus, upon excitation of cage 1 with 300 nm wavelength, fluorescence emission peak is detected at 439 nm, consistent with the known fluorescence emission of azulene. In addition, two shoulders were observed at 419 and 466 nm, which are likely due to vibronic transitions or multiple excited-state relaxations.

Changes in the electronic structure upon reduction caused a blue-shift of the absorption maxima. The recorded UV/vis spectrum of 2 showed absorption maximum at 288 nm and other medium absorption bands at 241, 352, and 371nm (Figure [5b]), which are shifted to lower wavelengths as compared to cage 1. The hexaamine cage emits at 384 nm and 400 nm upon excitation with 300 nm wavelength. This blue shift of the emission band is most likely caused by the loss of conjugation upon imine reduction, reflected also in a decrease of fluorescence intensity as compared to hexaimine cage.

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Figure 5 Absorption (red) and emission (black) spectra recorded for cage 1 (A) and 2 (B) recorded in CHCl3

Thus, the hexaimine cage with an extended electron conjugation has stronger absorption and stronger fluorescence due to more efficient radiative relaxation. The reduced hexaamine cage shows lower fluorescence intensity and hypsochromic shifts in both the UV/Vis and fluorescence spectra.

Azulene is known for its distinct redox behavior being able to both oxidize and reduce with the formation of radical anions and cations.[18] The redox properties of the two cages were investigated using cyclic voltammetry (CV) in anhydrous methanol containing 0.1 M tetrabutylammonium perchlorate as supporting electrolyte in the –2 to 2 V potential range. The electrochemical investigations were conducted at 0.1 V/s scan rate, using platinum disk electrode as working electrode and Pt wire as counter electrode, referred to Ag wire, used as quasi-reference electrode. In methanol, the response of cage 1 appears small compared to previous bistren type cryptand.[13] There are no sharp redox peaks; instead, broad current responses are seen (Figure S6, (SI). This suggests poor redox activity which might be due to the low solubility of the cage in methanol as solvent. Therefore, the cyclic voltammetry experiments were performed in a mixture chloroform:methanol. In this case, CV graph in Figure [6] shows quasi-reversible redox behavior, as indicated by the presence of distinct oxidation and reduction peaks. Two oxidation peaks are observed at 1.01 and 0.71 V, and reduction peaks at –0.63 V. These peaks correspond to the redox potentials of azulene moieties being similar to those observed in similar derivatives.[13] [19]

Zoom Image
Figure 6 Cyclic voltammetry experiments containing 0.1 M tetrabutylammonium perchlorate recorded for cage 1, 4.7·10–5 M in CHCl3/MeOH (5:1 v/v) (A) and cage 2, 4.1·10–5 M in MeOH (B) with a scan rate of 100 mV/s in the –2 to 2 V potential range.

The reduced hexaamine cage 2 showed a defined redox behavior in methanol solution, the current reaches up to 3 × 10–⁴ A, indicating enhanced electron transfer kinetics. The CV presents distinct peaks for the oxidation process. Two oxidation peaks are observed at 0.76 and 1.31 V. While the first one might correspond to the oxidation of electron-rich amine groups, the second one is characteristic for the oxidation of azulene π-system. The oxidation peaks around +1.3 V align well with azulene derivatives in protic solvents.[19]

In conclusion, by using azulene-dialdehyde as a linker and 1,3,5-tris(aminomethyl)-2,4,6-triethylbenzene as a triamine node, two types of macrobicyclic cages were isolated. By Schiff base condensation, a new [2+3] hexaimine cage was obtained. This cage shows a high symmetrical structure, both in solution and in solid state. The X-ray crystal structure revealed the formation of a bidimensional architecture assembled by π-π stacked azulene moieties and C–H···π interactions. The azulene units through extended π-conjugation induced absorption in the visible region and fluorescent properties of the hexaimine cage. Upon reduction with NaBH4, the corresponding macrobicyclic hexaamine was isolated. The chemical structure was assigned by NMR and high-resolution mass spectroscopy. The reduced cage showed a hypsochromic shift and decrease in fluorescence intensity, which suggests that the reduction of the imine groups to amines disrupts the conjugated system, leading to shorter absorption and emission wavelengths and a reduction in fluorescence efficiency. Both cages are redox active, the hexaamine cryptand showing higher current values, likely due to better electron transfer kinetics enabled by the flexible, reduced amine structure.

Azulene-1,3-dicarboxaldehydes was obtained following the Vilsmeier reaction.[20] Commercially available anhydrous solvents (MeOH and DMF) were purchased from Merck and used as received. CH2Cl2 was dried over CaH2. CDCl3 was kept over silver foil before use. 1,3,5-Tris(aminomethyl)-2,4,6-triethylbenzene trihydrochloride was purchased from Sigma-Aldrich and used as received. The IR spectra were collected using an ATR equipped Bruker Vertex V70 spectrometer in the 4000–400 cm–1 range. UV/vis spectra of the liquid samples were measured on a Varian Cary 100 spectrophotometer using 1 cm quarts cells. The solid samples were collected on a PerkinElmer Lambda 35 instrument. The high-resolution mass spectra were acquired with a QTOF LCMS-9030 mass spectrometer from Shimadzu (Kyoto, Japan), equipped with the ESI interface and auxiliary interface for calibration. The calibration was performed with a NaI solution. Samples dissolved in MeCN at a concentration of 1 ppm were infused directly into the ESI interface with an LC-40D × 3 pump at a flow rate of 0.4 mL/min with a mobile water phase (0.1% formic acid) 10% and MeCN. The sample solutions were loaded into a loop using a SIL-40C × 3 automatic injector. The injected volume was 1 μL. At the ESI interface, the nebulizing gas was N2 with a flow rate of 3 L/min, N2 was used as the drying gas with a flow rate of 10 L/min, the heating gas was air at a rate of 15 L/min, and the temperature of the ESI interface was 250 °C. The fluorescence emission spectra in solution were recorded with a Jasco FP-6500 spectrofluorometer, using 3 and 10 nm bandpass for the excitation and emission monochromators, a detector response of 1 s, a scanning speed of 100 nm min–1, and a data pitch of 1 nm, at an excitation wavelength of 300 nm. For both compounds, they were used as CHCl3 solutions, concentrations: 1.8·10–5 mM for cage 1 and 1.6·10–5 mM for cage 2. The NMR spectra were recorded on a Bruker Avance II 500 MHz (1H: 500 MHz, 13C: 175.47 MHz), Karlsruhe, Germany. The structural assignment of the 1H and 13C resonances was obtained from 1H COSY and 13C HSQC, and HMBQ experiments. Electrochemical measurements were carried out on a potentiostat-galvanostat system AutoLab Vionic powered by INTELLO software. Three electrodes in a one-compartment cell (50 mL) were used in all experiments. A platinum disk electrode (Metrohm, 3 mm in diameter) served as the working electrode. The counter electrode was a Pt wire of a large area. All experimental potentials were referred to Ag wire (Metrohm), used as a quasi-reference electrode. The electrochemical measurements were carried out in anhyd MeOH and CHCl3/MeOH (25/5 v/v) for cage 1, containing 0.1 M tetrabutylammonium perchlorate as the supporting electrolyte. The solutions containing the electroactive species and the supporting electrolyte were purged with argon for 20 min in order to remove the oxygen. X-ray diffraction measurements for crystals of 1 were performed on a Rigaku XtaLAB Synergy-S diffractometer operating with a Mo-Kα (λ = 0.71073 Å) microfocus sealed X-ray tube. The structures were solved by direct methods and refined by full-matrix least-squares techniques based on F2. The non-H atoms were refined with anisotropic displacement parameters. Calculations were performed using the SHELX-2014 or SHELX-2018 crystallographic software package.[21] A summary of the crystallographic data together with refinement details is presented in Table [1[22] (see above).


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Preparation of Cage 1

To a stirred solution of azulen-1,3-dialdehyde (33 mg, 0.18 mmol) in anhyd CH2Cl2 (20 mL) was added dropwise at rt under argon a solution of 1,3,5-tris(aminomethyl)-2,4,6-triethylbenzene trihydrochloride (43 mg, 0.12 mmol) and treated with Et3N (50 μL, 0.36 mmol) in anhyd MeOH (10 mL). The reaction was continued for 24 h, The green precipitate was filtered and the filtrate kept at rt for slow evaporation of the solvent mixture to give 34 mg (60%) of a green solid. The reaction can be scaled-up to three times with a slight decrease of the reaction yield to around 56%. As such, the reaction was performed with azulen-1,3-dialdehyde (99 mg, 0.54 mmol) in anhyd CH2Cl2 (75 mL) and 1,3,5-tris(aminomethyl)-2,4,6-triethylbenzene trihydrochloride (129 mg, 0.36 mmol) by treating with Et3N (100 μL, 0.11 mmol) in anhyd MeOH (20 mL); yield: 95 mg (56%, 0.10 mmol) of green precipitate.

IR: 2962 (m), 2929 (m), 1620 (vs), 1591 (s), 1523 (m), 1440 (vs), 1391 (s), 1319 (s), 1300 (s), 1237 (m), 1143 (m), 1003 (s), 972 (s), 802 (vs), 744 (vs), 578 cm–1 (m).

1H NMR (500 MHz): δ = 10.13 (d, J = 9.8 Hz, 6 H, H-4 and H-8), 8.18 (s, 6 H, CH=N), 7.83 (t, J = 9.8 Hz, 3 H, H-6), 7.58 (t, J = 9.9 Hz, 6 H, H-5 and H-7), 7.56 (s, 3 H, H-2), 5.23 (d, J = 1.4 Hz, 12 H, CH2), 3.42 (q, J = 7.3 Hz, 12 H, CH 2CH3), 1.30 (t, J = 7.3 Hz, 18 H, CH2CH 3).

13C NMR (125 MHz): δ = 155.24 (Cq), 155.12 (CH=N), 144.65 (Cq), 143.47 (C-2), 140.81 (C-6), 139.80 (C-4 and C-8), 131.02 (Cq), 129.35 (C-5 and C-7), 124.01 (Cq), 54.44 (CH2), 23.68 (CH2CH3), 16.29 (CH2 CH3).

HRMS (ESI+): m/z [M + H]+ calcd for C66H66N6: 943.54217; found: 943.54294.

UV/vis (CHCl3): λ (lg ε) = 244 (5.06), 290 (5.07), 317 (sh), 406 (4.51), 425 nm (4.42).


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Preparation of Cage 2

To a stirred solution of cage 1 (27 mg, 0.028 mmol) in anhyd CH2Cl2 (20 mL) was added a solution of NaBH4 (10 mg, 0.28 mmol) dissolved in MeOH (10 mL). The reaction was performed at rt, under argon atmosphere for 1 h. The solvent was removed under reduced pressure and the residue was dissolved in CHCl3. The CHCl3 layer was washed with H2O, dried (Na2SO4), and filtered over Celite; yield: 26 mg (93%); blue solid.

IR: 2959 (m), 2923 (m), 2865 (m), 1624 (vs), 1530 (m), 1488 (vs), 1370 (s), 1257 (m), 1079 (br), 876 (m), 733 cm–1 (vs).

1H NMR (500 MHz): δ = 8.19 (d, J = 9.6 Hz, 6 H, H-4 and H-8), 8.01 (s, 3 H, H-2), 7.50 (t, J = 9.6 Hz, 3 H, H-6), 7.01 (t, J = 9.6 Hz, 6 H, H-5 and H-7), 4.39 (s, 12 H, CH 2Az), 3.96 (s, 12 H, ArCH 2), 2.84 (q, J = 7.5 Hz, 12 H, CH 2CH3), 1.32 (t, J = 7.5 Hz, 18 H, CH2CH 3).

13C NMR (125 MHz): δ = 142.19 (Cq), 137.23 (C-6), 135.08 (Cq), 134.60 (C-2), 132.73 (C-4 and C-8), 132.60 (Cq), 128.11(Cq), 120.92 (C-5 and C-7), 48.64 (ArCH2), 48.30 (CH2Az), 22.61 (CH2CH3), 16.92 (CH2 CH3).

HRMS (ESI+): m/z [M + H]+ calcd for C66H70N6: 947.57347; found: 947.57353.

UV/vis (CHCl3): λ (lg ε) = 241 (3.08), 288 (4.18), 352 (3.25), 371 nm (3.25).


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Conflict of Interest

The authors declare no conflict of interest.

Acknowledgment

The financial support from the Ministry of Research, Innovation and Digitization, CNCS-UEFISCDI, project number PN-IV-P8-8.3-ROMD-2023-0045, within PNCDI IV is gratefully acknowledged. We are grateful to Dr. Maria Maganu for the IR spectroscopy measurements.

Supporting Information

    Supporting information for this article is available online at https://doi-org.accesdistant.sorbonne-universite.fr/10.1055/a-2593-4590.
  • Supporting Information

Corresponding Authors

Marius Andruh
C. D. Nenitzescu Institute of Organic and Supramolecular Chemistry
Splaiul Independentei 202B, 060023 Bucharest
Romania   

Simona Nica
C. D. Nenitzescu Institute of Organic and Supramolecular Chemistry
Splaiul Independentei 202B, 060023 Bucharest
Romania   

Publication History

Received: 31 March 2025

Accepted after revision: 23 April 2025

Accepted Manuscript online:
23 April 2025

Article published online:
22 May 2025

© 2025. Thieme. All rights reserved

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Zoom Image
Scheme 1 Schematic representation of the cages synthesis
Zoom Image
Figure 1 1H NMR spectrum of cryptand 1 recorded in CDCl3 at 298 K
Zoom Image
Figure 2 a) The asymmetric unit of cryptand 1 with atom labeling; b) top view of the propeller-like feature.
Zoom Image
Figure 3 Packing diagram in crystal 1: a) columns running along the crystallographic b axis; b) one dimensional supramolecular assembly formed by π-π stacked azulene moieties; c) two-dimensional architecture formed by π-π and C–H∙∙∙π interactions.
Zoom Image
Figure 4 1H NMR spectrum of hexaamine cryptand 2 recorded in CDCl3 at 298 K
Zoom Image
Figure 5 Absorption (red) and emission (black) spectra recorded for cage 1 (A) and 2 (B) recorded in CHCl3
Zoom Image
Figure 6 Cyclic voltammetry experiments containing 0.1 M tetrabutylammonium perchlorate recorded for cage 1, 4.7·10–5 M in CHCl3/MeOH (5:1 v/v) (A) and cage 2, 4.1·10–5 M in MeOH (B) with a scan rate of 100 mV/s in the –2 to 2 V potential range.