Structural Variations on Self-Assembly and Macroscopic Properties of 1,4,5,8-Naphthalene-diimide Chromophores

Abstract

Supramolecular assembly and macroscopic properties of a series of bis-(trialkoxybenzamide)functionalized naphthalene-tetracarboxylicacid-diimide (NDI) chromophores have been studied. The number of methylene units (0, 2, 3, 4; NDI-0, NDI-2, NDI-3, NDI-4, respectively) in between the NDI chromophore and the amide functionalities have been systematically varied to understand the effect of this simple structural variations on the self-assembly. UV-visible spectroscopic studies revealed facile self-assembly in nonpolar medium by synergistic effect of π-stacking, hydrogenbonding, and hydrophobic interactions. The propensity toward self-assembly was found to follow the order NDI-0 . NDI-2 ≈ NDI-3 > NDI-4 ,which could be attributed to the difference in strength of the H-bonding interaction. Atomic force microscopy (AFM) studies revealed unique morphology for the self-assembled structure in each case such as nanostructure with short-range order (NDI-0), elongated nanowires (NDI-2), relatively flat nanoribbons (NDI-3), and discontinuous nanofibers (NDI-4). Effect of such diverse morphologies was found to be highly relevant in correlating the macroscopic properties such as gelation of the individual chromophore. Most strongly aggregating NDI-0 did not show gelation in any of the tested solvents but formed lyotropic mesophases (chromonic N and M-phase) which could be related to their crystal like morphology as revealed by AFM images. Contrary to this, NDI-2 and NDI-3 showed most promising gelation ability in many common organic solvents with very low critical gelation concentrations (in some cases even <0.1 wt %) and NDI-4 formed gel only in few solvents which can be attributed to the strength of the selfassembly. The viscoelastic properties of the gels were studied by rheological measurements which revealed remarkable dependence on the morphology of the self-assembled structure. For example, although the self-assembly propensity and gelation ability were almost similar between NDI-2 and NDI-3, the yield-stress of the former gel was estimated to be astonishingly high (∼20 times) compared to that of NDI-3 gel owing to the large differences in the aspect ratio of the respective 1Dnanostructures. Further the thermodynamic parameters such as ΔH m (enthalpy of melting) of the gel-to-sol transition were determined for various gels and correlated with the molecular structure and self-assembly propensity in solution.

Formation of Hybrid Hydrogels Consisting of Tripeptide and Different Silver Nanoparticle-Capped Ligands: Modulation of the Mechanical Strength of Gel Phase Materials

“…Generally, the yield stress values of supramolecular hydrogel are less; 69−72 however, the yield stress value obtained from our tripeptide-based hydrogel is comparable to other supramolecular gels. 72 A high storage modulus (G′) and high yield stress (σ y ) values indicate the formation of a significantly rigid gel material.…”

Hydrogen‐Bonding‐Mediated J‐Aggregation and White‐Light Emission from a Remarkably Simple, Single‐Component, Naphthalenediimide Chromophore

“…[5,6] Considering structural simplicity and versatile hydrogenbonding motifs of carboxylic acid group as described in the literature related to crystal engineering, [7] we envisaged it would be worth exploring its utility as a structure-directing functionality in self-assembly of organic functional p-systems. In the recent past, we have been engaged in understanding effect of structural variations on hydrogen-bonding mediated self-assembly of 1,4,5,8-naphthalenetetracarboxdi-A C H T U N G T R E N N U N G imide (NDI) derivatives [8] due to the prospect of using this particular chromophore [9] as an n-type semiconductor. [10] NDI derivatives have also been extensively utilized as building blocks for various elegant supramolecular materials, such as synthetic ion channels, [11] organogels, [8,12] hydrogels, [13] nanotubes, [6,14] catenanes, [15] rotaxanes, [16] foldamers, [17] supramolecular photosystems, [18] nanoparticles, [19] and other amphiphilic nanostructures.…”

“…In the recent past, we have been engaged in understanding effect of structural variations on hydrogen-bonding mediated self-assembly of 1,4,5,8-naphthalenetetracarboxdi-A C H T U N G T R E N N U N G imide (NDI) derivatives [8] due to the prospect of using this particular chromophore [9] as an n-type semiconductor. [10] NDI derivatives have also been extensively utilized as building blocks for various elegant supramolecular materials, such as synthetic ion channels, [11] organogels, [8,12] hydrogels, [13] nanotubes, [6,14] catenanes, [15] rotaxanes, [16] foldamers, [17] supramolecular photosystems, [18] nanoparticles, [19] and other amphiphilic nanostructures. [20] As a part of our continuing interest in self-assembly of NDI chromophore, we synthesized NDI-1 (Figure 1), which contains a carboxylic acid group that is capable of forming a self-complementary hydrogen-bonding network and a dodecyl chain to provide enhanced solubility in relatively nonpolar solvents.…”

Added‐Value Surfactants

“…They could show the formation of liquid crystalline phases in mixtures of chloroform and methylcyclohexane, indicating a wide‐range order under distinct conditions . The group of Nakanishi et al.…”

“…They could show the formation of liquid crystalline phases in mixtures of chloroform and methylcyclohexane, indicating a wide-range order under distinct conditions. [25] The group of Nakanishi et al used the fullereneC 60 as as olvophobic entity, which was modified by "ordinary" hydrophobic groups. [26] Upon solvation in n-hexane self-assembly takes place as indi-cated by X-ray methods and cross-polarizationm icroscopy.T he tendency of C 60 to exhibit p-p-interactions is relativelys mall.…”