Contrasting Self‐Assembly and Gelation Properties among Bis‐urea‐ and Bis‐amide‐Functionalised Dialkoxynaphthalene (DAN) π Systems

Abstract

Precise control over the spatial arrangement of various functional chromophores [1] plays an important role in modulating the inter-chromophoric interactions and consequently the photophysical properties. The motivation to study these properties stems from the desire to understand the effect of molecular-level interactions on macroscopic properties because of the relevance in organic electronic device applications.[2] In the recent past, there have been many efforts aimed towards developing suitable supramolecular strategies for achieving long-range order in the self-assembled structure of various p systems, such as p- [3] and n-type [4] semiconductors, push-pull-type chromophores, [5] and donor-acceptor charge-transfer systems.[6] The design of the building blocks in most of these systems ensure that self-assembly can be facilitated by gaining the synergistic effect of several non-covalent forces, such as p-p interactions, hydrogen bonding, dipole-dipole interactions, and the hydrophobic effect. In most cases, the role of hydrogen-bonding functionalities has been restricted only to strengthen the propensity for self-assembly, except for a few recent examples in which the nature of the chromophore arrangements could be drastically changed (H-vs. J-type aggregation) by varying the peripheral functional groups [7] or the hydrogen-bonding motif. [8] Amide and urea are the two most common self-complementary hydrogen-bonding motifs and have been extensively used for various dye assemblies. [3][4][5] However, to the best of our knowledge there have not been any studies to exclusively compare the influence of these two functionalities in deciding the chromophoric arrangements in the self-assembled structure. The question we asked is whether, due to the mismatch in number of hydrogen-bonding ( À NH···O À ) interaction sites, they only differ in terms of providing differential stability to the self-assembled structure or are they also capable of altering the mode of the chromophoric arrangements? To answer this question, we have synthesised two derivatives of the dialkoxynaphthalene (DAN) p system, namely, DAN-U and DAN-A (Scheme 1), which differ only in amide and urea functionalities. Herein, we report the contrasting solution self-assembly and gelation behaviour of DAN-U and DAN-A and our studies related to understanding the correlation between these two phenomena.Firstly, we studied the self-assembly in solution by solvent-dependent absorption spectroscopy. In a recent report we have shown that DAN-A forms H-type p stacks in nonpolar medium such as methylcyclohexane (MCH)/CHCl 3 (95:5).[9] However, DAN-U was found to be insoluble in CHCl 3 at room temperature and so to avoid ambiguity in the comparative self-assembly studies in solution, herein we have used a THF and MCH solvent composition.In Figure 1 a, we show the UV-visible absorption spectral changes of DAN-A as a function of solvent composition. With gradual addition of non-polar solvent MCH to the solution of the chromophore in THF, there was almost no cha...

Chiral induction by helical neighbour: spectroscopic visualization of macroscopic-interaction among self-sorted donor and acceptor π-stacks

“…To confirm that the new band appears due to self-assembly of DAN-1, the CD spectrum of the mixture was examined at an intermediate temperature (55 1C) where self-assembly of NDI-1 should remain intact, but the relatively less-stable p-stacked assembly DAN-1 should be converted to monomers. 8,13 In Fig. 3a, it can be clearly seen that at 55 1C the additional bands in the CD-spectrum corresponding to the donor-absorption disappear (blue line) and the spectrum is very similar to that observed for NDI-1 alone (black line).…”

“…S4w) which indicated J-type p-stacking. 13 The CD-spectra of NDI-1 + DAN-2 in 95 : 5 MCH-CHCl 3 was found to be fully matching to that for NDI-1 alone (Fig. S7w).…”

Supramolecular Clippers for Controlling Photophysical Processes through Preorganized Chromophores

“…Upon binding of DAN‐Bola with increasing equivalents of adenosine triphosphate (ATP), a trivalent clipper molecule, a gradual bathochromic shift (2 nm), a decrease in absorbance, and a slight scattering at higher wavelength were observed, which are clear signatures of J‐type interchromophoric organization in dialkoxynaphthalene derivatives (Figure 1 a). 15 Quite surprisingly, the corresponding emission spectra showed a gradual decrease in the monomeric emission at 342 nm, with the simultaneous evolution of a significantly bathochromic emission band at 472 nm, which is 130 nm redshifted relative to the monomeric emission, with an isoemissive point at 389 nm (Figure 1 b). Such a redshifted broad emission band with high fluorescence intensity and without any vibrational features is characteristic of excimer emission, which is well known in NDI‐, naphthalene‐, or pyrene‐derived chromophores 16.…”

Preparation of dicholesteryl-derivatives: The effect of spatial configuration upon gelation

“…It can be seen for both systems that initial G′ is higher than G″ by around one order of magnitude, suggesting the presence of gel phase. With a gradual increase in the applied stress, both G′ and G″ remained invariant and then beyond a certain stress, defined as the yield stress, they deviated from linearity, demonstrating that gels began to flow [42,45]. The yield stresses for FaDC and FaLC were estimated to be 70 and 11 Pa, respectively.…”