pH‐Responsive Side Chains as a Tool to Control Aqueous Self‐Assembly Mechanisms

Abstract

pH-Tunable nanoscale morphologya nd self-assembly mechanism of as eries of oligo(p-phenyleneethynylene)( OPE)-based bolaamphiphiles featuring poly(ethylene imine) (PEI) side chains of differentl ength and degree of hydrolysis are described. Protonation and deprotonation of the PEI chainsb yc hanging the pH alters the hydrophilic/hydrophobic balance of the systems and, in turn, the strength of intermoleculari nteractions between the hydrophobic OPE moieties. Low pH values (3) lead to weak interaction betweent he OPEs and resulti ns pherical nanoparticles, in whicha ggregation follows an isodesmic mechanism. In contrast, higherp Hv alues (11) induce deprotonation of the polymer chains and lead to as tronger, cooperativea ggregation into anisotropic nanostructures. Our resultsd emonstrate that pH-responsive chains can be exploited as at ool to tune self-assemblymechanisms, which opens exciting possibilities to develop new stimuliresponsive materials. Supramolecular polymerization enables the creation of functional materials with multiple potentiala pplicationsi nvarious fields including optoelectronics or life sciences. [1] This bottomup approachr elies on the use of dynamic and reversible noncovalenti nteractions, which provides the system with outstanding properties, such as responsivenesst oe xternals timuli or self-healing. [2] Meanwhile, detailed mechanistic investigations of supramolecular polymerization processes have been reported for different types of buildingb locks. [3] The majority of these systemsc an be described by two main polymerization mechanisms-isodesmic and cooperative. [4] The determinants of ag iven mechanistic pathway are the type and number of non-covalent interactions. [5] Although supramolecularp olymers only exhibiting p-p stacking are usually described by the isodesmic mechanism, the combination of p-stacking and Hbondingg enerally guarantees ac ooperative mechanism,p rovided that no strong repulsive effectsa re present. [6] Regulation of these mechanismsi sahot topic in current research, which is possible by alteringthe molecular design or by adjusting the physicalp arameters (temperature, solvent, and/orc oncentration) to preparet he aggregate solution. However,p redicting the type of self-assembly mechanismb ym olecular design is still challenging, and the development of advanced self-assembled systemsw ith tailoredm echanismsi saprerequisite to generalize this trend.Previously,o ur groups reported that the self-assembly mechanism (isodesmic vs.c ooperative) of polymer-functionalized OPE-based bolaamphiphiles in aqueous mediac an be directly correlated with the polymer chain length. [7] This molecular engineering methode nables the fine tuning of the hydrophilic/ hydrophobic balance,w hich in turn determines the aggregate morphology (organized 2D lamellae vs. disorganizedn anoparticles). These findingsp rompted us to investigate whether the hydrophilic/hydrophobicr atio and the resulting aggregation behavior could also be controlled by pH changes. In that regard, pH-responsive pol...

Thiosquaramide-Based Supramolecular Polymers: Aromaticity Gain in a Switched Mode of Self-Assembly

“…Moreover, the weak red-shifted shoulder observed experimentally at 420 nm is consistent with other supramolecular polymers involving stacked chromophores that exhibit a rotational offset in the aggregated state. 41 …”

“…In the case of 2′ and 2a , supramolecular polymerization results in a blue-shift of the monomer absorbance spectra that can be ascribed to the formation of an H-type aggregate with a parallel arrangement of transition dipole moments, suggesting a cofacial orientation of the thiosquaramide units. Moreover, the weak red-shifted shoulder observed experimentally at 420 nm is consistent with other supramolecular polymers involving stacked chromophores that exhibit a rotational offset in the aggregated state …”

“…Moreover, the weak red-shifted shoulder observed experimentally at 420 nm is consistent with other supramolecular polymers involving stacked chromophores that exhibit a rotational offset in the aggregated state. 41 An alternative explanation for the observed shifts in the absorbance spectra results from analyzing the symmetry of the π-orbitals involved in the UV transitions. In the head-to-tail hexamer of 1′, the HOMO and LUMO orbitals of neighboring monomers are out-of-phase, and thus, disrupting this disfavored interaction leads to a red-shifted HOMO → LUMO transition (the peak at 258.2 nm shifts to 263.3 nm) upon disassembly.…”

Impact of Ring-Closing on the Photophysical Properties of One-Dimensional π-Conjugated Molecular Aggregate

“…In this study, we focus on how circular structures of organic matter at a larger scale (i.e., in the mesoscale range) affect the properties of the constituent molecules. Our strategy to construct such mesoscale organic structures is based on one-dimensional aggregation (supramolecular polymerization) of functional molecules. − Supramolecular polymerization has been developed and exploited in the past two decades to prepare macromolecular materials with a wide range of applications including stimuli-responsive soft materials, − electronic devices, − and biofunctional materials. − In most cases, supramolecular polymer main chains have either no specific higher-order structure (those based on multiple hydrogen bonds or host–guest interactions) or a one-dimensional cylindrical structure (those based on functional molecules with multiple noncovalent interactions). On the other hand, the supramolecular polymers we have studied in this decade elongate with a curvature diameter of about 20 nm (Figure a–c). , Consequently, by modulating the supramolecular polymerization protocol, we can prepare cyclic, randomly coiled, and helically coiled mesoscopic structures.…”

Chiral information harvesting in helical poly(acetylene) derivatives using oligo(p-phenyleneethynylene)s as spacers

“…2). 34,47 Additional structural studies were carried out in poly-(S)-2 and poly-(S)-3 to obtain an approximated secondary structure of these polymers and determine their dynamic behaviour.…”