Supramolecular Aggregation/Deaggregation in Amphiphilic Dipolar Schiff-Base Zinc(II) Complexes

Abstract

The synthesis, characterization, optical, and fluorescent properties of an amphiphilic Schiff-base bis(salicylaldiminato)zinc(II) complex are reported. Detailed (1)H nuclear magnetic resonance (NMR), diffusion-ordered spectroscopy (DOSY) NMR, optical absorption, and fluorescence spectroscopy studies indicate the existence of aggregate species in noncoordinating solvents. The degree and type of aggregation are related to the concentration and the polarity of the noncoordinating solvent. Dilute solutions are likely characterized by the presence of defined dimers, whereas larger oligomeric aggregates are conceivably formed at higher concentrations. The concentration needed to observe the formation of larger species depends upon solvent polarity. In coordinating solvents or in the presence of coordinating species, a complete deaggregation of the system occurs, because of the axial coordination to the Zn(II) ion, accompanied by considerable changes of (1)H NMR and optical absorption spectra. A dramatic enhancement of fluorescence emission is observed in dichloromethane solutions upon deaggregation with a coordinating agent. The formation of a defined 2:1 supramolecular structure is demonstrated in the case of a ditopic ligand as coordinating species. Overall, these complexes are promising systems for the development of new supramolecular architectures and supramolecular fluorescent probes.

Supramolecular Aggregation of a New Substituted Bis(salicylaldiminato)zinc(II) Schiff-Base Complex Derived from trans-1,2-Diaminocyclohexane

“…The synthesis of (R)-2 was carried out by standard template method [5][6][7][8][9][10], using 4-(diethylamino)-2-hydroxybenzaldehyde and (1R,2R)-trans-1,2-diaminocyclohexane in methanol solution and a stoichiometric excess of triethylamine. Then, complexation with the Zn(II) ion was accomplished by using zinc perchlorate.…”

“…To further investigate about the structure of (R)-2 in solution, we performed diffusion-ordered NMR spectroscopy (DOSY) measurements, by using a known internal reference to estimate the molecular mass of species in solution [5][6][7][8][9][10]. The DOSY spectrum of (R)-2 in DMSO-d 6 (1.0 × 10 −2 M) confirms the presence of a single component in the diffusion dimension (D = 2.5 × 10 −10 m 2 ·s -1 ), with an estimated molecular mass (679 Da) consistent with the (R)-2·DMSO adduct ( Table 1).…”

“…All NMR experiments were recorded at 27 °C on a Varian Unity S 500 spectrometer (Varian, Palo Alto, CA, USA), using tetramethylsilane (Si(CH3)4, TMS) as an internal reference. DOSY experiments were performed as reported elsewhere [5][6][7][8][9][10]. Optical absorption and CD spectra were recorded at room temperature using a UV-VIS Jasco V-630 spectrophotometer (Jasco Europe, Cremella (LC), Italy) and a Jasco 810 spectropolarimeter (Jasco Europe, Cremella (LC), Italy), respectively.…”

A Cryptand-Type Aluminum Tris(salophen) Complex: Synthesis, Characterization, and Cell Imaging Application

“…In our group, a series of Zn salen/salophen complexes have been reported as fluorescent probes for cell imaging even with super-resolution, with multiple functions such as intracellular reactive oxygen species, monitoring the lipid droplets and autophagy processes [17][18][19][20][21][22][23]. However, Zn salen complexes tend to aggregate through the axial intermolecular interactions between the Zn center and the phenolic oxygen of another molecule, especially in non-coordinating solvents [24][25][26][27][28][29]. The aggregation not only weakens fluorescence intensity, but also influences the cellular uptake pathway and subcellular localization [30].…”

Synthesis, Characterization and Property Studies on a Dinuclear Copper(II) Complex with Dipyridine Derivate and Acetylacetone

“…[1][2][3][4] The most efficient and widely used approach for designing such material is the self-assembly of organic ligands and metal ions, and the type/topology of the products generated from this process can be tuned by a judicious choice of the ligands, [5][6] metal coordination geometry preference, counter ion, [6][7][8] solvent, [8][9] metal to ligand ratio [10][11] and temperature. 12 Among these, the choice of organic ligand is one of the important factors.…”