How Subtle Changes Can Make a Difference: Reproducibility in Complex Supramolecular Systems

Abstract

The desire to construct complex molecular systems is driven by the need for technological (r)evolution and our intrinsic curiosity to comprehend the origin of life. Supramolecular chemists tackle this challenge by combining covalent and noncovalent reactions leading to multicomponent systems with emerging complexity. However, this synthetic strategy often coincides with difficult preparation protocols and a narrow window of suitable conditions. Here, we report on unsuspected observations of our group that highlight the impact of subtle "irregularities" on supramolecular systems. Based on the effects of pathway complexity, minute amounts of water in organic solvents or small impurities in the supramolecular building block, we discuss potential pitfalls in the study of complex systems. This article is intended to draw attention to often overlooked details and to initiate an open discussion on the importance of reporting experimental details to increase reproducibility in supramolecular chemistry.

Self‐assembly of chiral diketopyrrolopyrrole chromophores giving supramolecular chains in monolayers and twisted microtapes

“…Although we were unable to check the enantiomeric excess of the chiral compounds made here (their high polarity and their limited solubility in appropriate solvents for chromatography made this impractical in our hands), the optical activity observed by circular dichroism (CD) spectroscopy indicates similar enantiopurity (see below). Despite appearing clean by nuclear magnetic resonance spectroscopy (NMR) and elemental analysis, the first attempts at synthesis of PhO( R,R ) EP DPP NH and PhO( S,S ) EP DPP NH resulted in compounds that exhibited slightly different CD spectra (and only PhO( S,S ) EP DPP NH gave rise to a CPL signal in the first isolated materials, see below), indicating a slight chemical or optical impurity 84,85 . The fact that after optimization the compounds were purified by precipitation, a process that would be expected to favor a high enantiomeric purity, and the process does give materials with mirror image CD spectra, supports that hypothesis.…”

2D self-assembly ofo-OPE foldamers for chiroptical barcoding

“…This abnormal behaviour could be due to diverse and complex contribution of the intermolecular interactions between the molecules forming the monolayer and with the water molecules. 51…”

“…This abnormal behaviour could be due to diverse and complex contribution of the intermolecular interactions between the molecules forming the monolayer and with the water molecules. 51 The microscopic morphology of the monolayers could be observed in situ at the air/water interface using Brewster Angle Microscopy (BAM), see Fig. 2B and Fig.…”

Chiral Supramolecular Polymers Assembled from Conformationally Flexible Amino‐Acid‐Substituted Biphenyldiimides

“…This is mainly due to the inherent weakness of the supramolecular assemblies, where a lot of factors such as molecular conformations, [ 14 ] solute‐solvent interactions, [ 15 ] guest molecules, [ 16 ] or the type of the side chains [ 17 ] may affect the self‐assembly outcome. [ 18 ]…”

“…This is mainly due to the inherent weakness of the supramolecular assemblies, where a lot of factors such as molecular conformations, [14] solute-solvent interactions, [15] guest molecules, [16] or the type of the side chains [17] may affect the self-assembly outcome. [18] In contrast to the well-known rigid and flat diimides, biphenyldiimides (BPDIs) [19] with significant flexibility around the single bond of the central aromatic core are much less explored but recently attracted attention as the versatile building blocks for the generation of nanooptic, [20] nanoelectronic, [21] and photocatalytic [22] materials. While those intramolecular motions might be restricted either by the introduction of bulky substituents, [23] or cyclization, [20,21,24] to the best of our knowledge, the unrestricted BPDIs have not yet been successfully employed in the formation of chiral supramolecular polymers.…”