Living supramolecular polymerization achieved by collaborative assembly of platinum(II) complexes and block copolymers

Metallosupramolecular Multiblock Copolymers of Lanthanide Complexes by Seeded Living Polymerization

Supramolecular block copolymers, derived via seeded living polymerization, are increasingly recognized for their rich structural and functional diversity, marking them as cutting-edge materials. The use of metal complexes in supramolecular block copolymerization not only offers a broad range of block copolymers through the structural similarity in the coordination geometry of the central metal ion but also controls spectroscopic properties, such as emission wavelength, emission strength, and fluorescence lifetime. However, the exploration of metallosupramolecular multiblock copolymerization based on metal complexes remains quite limited. In this work, we present a pioneering synthesis of metallosupramolecular multiblock copolymers utilizing Eu3+ and Tb3+ complexes as building blocks. This is achieved through the strategic manipulation of nonequilibrium self-assemblies via a living supramolecular polymerization approach. Our comprehensive exploration of both thermodynamically and kinetically regulated metallosupramolecular polymerizations, centered around Eu3+ and Tb3+ complexes with bisterpyridine-modified ligands containing R-alanine units and a long alkyl group, has highlighted intriguing behaviors. The monomeric [R-L1Eu(NO3)3] complex generates a spherical structure as the kinetic product. In contrast, the monomeric [R-L1Eu2(NO3)6] complex generates fiber aggregates as a thermodynamic product through intermolecular interactions such as π-π stacking, hydrophobic interaction, and H-bonds. Utilizing the Eu3+ complex, we successfully conducted seed-induced living polymerization of the monomeric building unit under kinetically regulated conditions. This yielded a metallosupramolecular polymer of precisely controlled length with minimal polydispersity. Moreover, by copolymerizing the kinetically confined Tb3+ complex state ("A" species) with a seed derived from the Eu3+ complex ("B" species), we were able to fabricate metallosupramolecular tri- and pentablock copolymers with A-B-A, and B-A-B-A-B types, respectively, through a seed-end chain-growth mechanism.

Living Growth Kinetics of Polymeric Micelles on a Substrate

Living growth of micelles on the substrate is an intriguing phenomenon; however, little is known about its growth kinetics, especially from a theoretical viewpoint. Here, we examine the living growth kinetics of polymeric micelles on a hydrophobic substrate immersed in an aqueous solution. The block copolymers first assemble into short cylinder seeds anchored on the substrate. Then, the small aggregates of block copolymers in the solutions fuse onto the active ends of the anchored seeds, leading to micelle growth on the substrate. A theoretical model is proposed to interpret such living growth kinetics. It is revealed that the growth rate coefficient on the substrate is independent of the copolymer concentration and the multistep feedings; however, it is significantly affected by the surface hydrophobicity. Brownian dynamics simulations further support the proposed growth mechanism and the kinetic model. This work enriches living assembly systems and provides guidance for fabricating bioinspired surface nanostructures.

Strategies for Synthesizing Supramolecular Block Copolymers

Over the past decade, controlled supramolecular polymerization has been extensively studied and gradually shifted to supramolecular block copolymerization. Supramolecular block copolymers (BCPs) are considered the holy grail for developing supramolecular materials with new functionalities due to their fascinating structures and ability to introduce diverse functions. From a thermodynamic view to kinetic aspects, great progress has been made in the synthetic strategies of BCPs in the past few years. This Concept summarizes various strategies to realize supramolecular block copolymerization. The focus is on providing researchers with a methodological basis for achieving heterogeneous nucleation-elongation.

A Kinetic Investigation of the Supramolecular Chiral Self-Assembling Process of Cationic Organometallic (2,2':6',2″-terpyridine)methylplatinum(II) Complexes with Poly(L-glutamic Acid)

The cationic platinum(II) organometallic complex [Pt(terpy)Me]+ (terpy = 2,2':6',2″-terpyridine) at mild acidic pH interacts with poly(L-glutamic acid) (L-PGA) in its α-helix conformation, affording chiral supramolecular adducts. Their kinetics of formation have been investigated in detail as a function of the concentrations of both reagents and changing pH, ionic strength, the length of the polymeric scaffold and temperature. After a very fast early stage, the kinetic traces have been analyzed as three consecutive steps, suggesting a mechanism based on the electrostatic fast formation of a not-organized aggregate that subsequently evolves through different rearrangements to form the eventual supramolecular adduct. A model for this species has been proposed based on (i) the attractive electrostatic interaction of the cationic platinum(II) complexes and the polyelectrolyte and (ii) the π-stacking interactions acting among the [Pt(terpy)Me]+ units.

Three-Component Multiblock 1D Supramolecular Copolymers of Ir(III) Complexes with Controllable Sequences

Multicomponent supramolecular block copolymers (BCPs) have attracted much attention due to their potential functionalities, but examples of three-component supramolecular BCPs are rare. Herein, we report the synthesis of three-component multiblock 1D supramolecular copolymers of Ir(III) complexes 1-3 by a sequential seeded supramolecular polymerization approach. Precise control over the kinetically trapped species via the pathway complexity of the monomers is the key to the successful synthesis of BCPs with up to 9 blocks. Furthermore, 5-block BCPs with different sequences could be synthesized by changing the addition order of the kinetic species during a sequentially seeded process. The corresponding heterogeneous nucleation-elongation process has been confirmed by the UV/Vis absorption spectra, and each segment of the multiblock copolymers could be characterized by both TEM and SEM. Interestingly, the energy transfer leads to weakened emission of 1-terminated and enhanced emission of 3-terminated BCPs. This study will be an important step in advancing the synthesis and properties of three-component BCPs.

Metallosupramolecular polymers: current status and future prospects

Metallo-supramolecular polymers have gained increasing attention and witnessed continuous development as a vibrant new research interest in the domain of soft materials. These nonconventional polymers have found widespread application in materials and biology owing to their well-defined and diversified topologies and the distinct dynamic nature of the metallosupramolecular interactions against various stimuli. Because of the intriguing redox, photonic, electronic, and magnetic properties, these stimuli-responsive supramolecular structures have attracted considerable interest for optoelectronic device fabrication. However, it still remains challenging to develop stimuli responsive systems with offbeat applications. Furthermore, achieving spatiotemporal control remains elusive with thermoresponsive and sono-responsive metallosupramolecular polymers, which encounter the disadvantage of poor precision control. Additionally, controlling the morphology of these soft materials on the mesoscale, both in solution and on substrates, has many challenges. In this review, we discuss the recent developments and future directions for the construction of stimuli responsive metallosupramolecular systems targeting practical applications. Furthermore, we discuss the synthetic methodologies that have been used to regulate the mesoscale morphology of these materials, such as coordination modulation and pseudomorphic replication. Finally, we briefly cover the burgeoning field of programmed synthesis of metallosupramolecular polymers, emphasizing techniques, such as living polymerization and chemical fuel-driven transiently active systems, which we believe will be the major research directions in the future.

Dynamic Control over Hierarchically Dendritic Architectures of Simple Heterogenous Monomers by Living Supramolecular Assembly

The successful preparation of supramolecular block copolymers (SBCPs) by living supramolecular assembly technology requires two kinetic systems in which both the seed (nucleus) and heterogenous monomer providers are in non-equilibrium. However, employing simple monomers to construct the SBCPs via this technology is almost impossible because the low spontaneous nucleation barrier of simple molecules prevents the formation of kinetic states. Here, with the help of confinement from layered double hydroxide (LDH), various simple monomers successfully form living supramolecular co-assemblies (LSCA). LDH overcomes a considerable energy barrier to obtain living seeds to support the growth of the inactivated second monomer. The ordered LDH topology is sequentially mapped to the seed, second monomer, and binding sites. Thus, the multidirectional binding sites are endowed with the ability to branch, making the branch length of dendritic LSCA reach its maximum value of 3.5 cm so far. The strategy of universality will guide exploration into the development of multi-function and multi-topology advanced supramolecular co-assemblies.

Luminescence and Length Control in Nonchelated d 8 ‐Metallosupramolecular Polymers through Metal‐Metal Interactions

Supramolecular polymers (SPs) of d⁸ transition metal complexes have received considerable attention by virtue of their rich photophysical properties arising from metal‐metal interactions. However, thus far, the molecular design is restricted to complexes with chelating ligands due to their advantageous preorganization and strong ligand fields. Herein, we demonstrate unique pathway‐controllable metal‐metal‐interactions and remarkable ³MMLCT luminescence in SPs of a non‐chelated Pt^II complex. Under kinetic control, self‐complementary bisamide H‐bonding motifs induce a rapid self‐assembly into non‐emissive H‐type aggregates (1A). However, under thermodynamic conditions, a more efficient ligand coplanarization leads to superiorly stabilized SP 1B with extended Pt⋅⋅⋅Pt interactions and remarkably long ³MMLCT luminescence (τ^77 K=0.26 ms). The metal‐metal interactions could be subsequently exploited to control the length of the emissive SPs using the seeded‐growth approach.

Boosting Organic Afterglow Performance via a Two-Component Design Strategy Extracted from Macromolecular Self-Assembly

Because intersystem crossing and phosphorescence decay are spin-forbidden in organic systems, it is challenging to obtain high-performance organic afterglow materials. Inspired by two-component design strategy from macromolecular self-assembly, here we report the utilization of synthetic polymers to control the excited state properties of difluoroboron β-diketonate (BF₂bdk) and deuterated BF₂bdk compounds for the fabrication of room-temperature organic afterglow materials. The polymer component can interact with BF₂bdk excited states by dipole-dipole interactions, lower BF₂bdk S₁ levels with insignificant effect on T₁ levels, reduce ΔE_ST, and thus enhance intersystem crossing of BF₂bdk excited states. The polymer component can also suppress intramolecular motion of BF₂bdk triplets and protect BF₂bdk triplets from oxygen quenching. The obtained BF₂bdk-polymer afterglow materials exhibit emission lifetimes up to 2.2 s and high photoluminescence quantum yields under ambient conditions, display excellent processability and flexibility, and can function as efficient donors for excited state energy transfer to construct red afterglow materials.

Vapor-Phase Living Assembly of π-Conjugated Organic Semiconductors

In contrast to well-studied amphiphilic block copolymers (BCPs) and π-stacked dyes, living assembly of hydrophobic π-conjugated materials has not yet been explored to date. Using a microspacing physical vapor transport (PVT) technique, the prefabricated microrods of organic semiconductors involving 9,10-dicyanoanthracene (DCA, A) or its binary alloy (B) can act as seeds to initiate living homoepitaxial growth from their ends, giving elongated microrods with controlled length. Red-green-red tricolor fluorescent microrod heterostructures with low dispersity are further realized by living heteroepitaxial growth of B microrod blocks on A seed microrod tips. Upon varying the growth sequence of each block, reverse triblock microrods are also accessible. Such a seed-induced living growth is applicable to triblock microrod heterostructures of more binary combinations as well as even more complex penta- and hepta-block heterostructures comprising A and B. By virtue of a convenient vapor-phase growth method, the present work demonstrates the generality of living assembly of π-conjugated materials.

Intense Organic Afterglow Enabled by Molecular Engineering in Dopant-Matrix Systems

We report intense dopant-matrix afterglow systems with an afterglow efficiency (Φ_AG) of 47% and an afterglow lifetime (τ_AG) of 1.3 s. Luminescent difluoroboron β-diketonate (BF₂bdk) dopants and their deuterated counterparts are designed with naphthalene and carboxylic acid groups. After doping into benzoic acid (BA) matrices, room-temperature afterglow brightness and afterglow duration of the BF₂bdk-BA materials have unexpectedly been found to reach the levels of those at 77 K, which indicates that hydrogen bonding between BF₂bdk and BA, as well as the deuteration technique, can reduce k_nr + k_q of BF₂bdk triplets to very small values even at room temperature. Detailed studies reveal that the BF₂bdk possesses typical ¹ICT characters in the S₁ state and distinct ³LE composition in the T₁ state, and thus shows a high Φ_ISC and a small k_P to obtain a high Φ_AG and a long τ_AG. Besides, triplet-triplet annihilation has been found in the dopant-matrix system at high doping concentrations to further increase Φ_AG.

Exploiting halido ligands to control nucleation pathways and Pt⋯Pt interactions in supramolecular co-polymerizations

We exploit halogen effects to tune metal–metal interactions, nucleation pathways and hetero-seeded growth in supramolecular copolymerizations.

Efficient long-range triplet exciton transport by metal-metal interaction at room temperature

Efficient and long-range exciton transport is critical for photosynthesis and opto-electronic devices, and for triplet-harvesting materials, triplet exciton diffusion length ( [[EQUATION]] ) and coefficient ( [[EQUATION]] ) are key parameters in determining their performances. Herein, we observed that PtII and PdII organometallic nanowires exhibit long-range anisotropic triplet exciton LD of 5-7 μm along the M-M direction using direct photoluminescence (PL) imaging technique by low-power continuous wave (CW) laser excitation. At room temperature, via a combined triplet-triplet annihilation (TTA) analysis and spatial PL imaging, an efficient triplet exciton diffusion was observed for the PtII and PdII nanowires with extended close M-M contact, while is absent in nanowires without close M-M contact. Two-dimensional electronic spectroscopy (2DES) and calculations revealed a significant contribution of the delocalized 1/3[dσ*(M-M)→π*] excited state during the exciton diffusion modulated by the M-M distance.

π-Conjugated-polymer-based nanofibers through living crystallization-driven self-assembly: preparation, properties and applications

π-Conjugated-polymer-based nanofibers (CPNFs) of controlled length, composition and morphology are promising for a broad range of emerging applications in optoelectronics, biomedicine and catalysis, owing to the morphological merits of fiber-like nanostructures and structural attributes of π-conjugated polymers. Living crystallization-driven self-assembly (CDSA) of π-conjugated-polymer-containing block copolymers (BCPs) has emerged as an efficient strategy to prepare CPNFs with precise dimensional and structural controllability by taking advantage of the crystallinity of π-conjugated polymers. In this review, recent advances in the generation of CPNFs have been highlighted. The influence of the structure of π-conjugated-polymer-containing BCPs and experimental conditions on the CDSA behaviors, especially seeded growth and self-seeding processes of living CDSA, has been discussed in detail, aiming to provide an in-depth overview of living CDSA of π-conjugated-polymer-containing BCPs. In addition, the properties of CPNFs as well as their potential applications have been illustrated. Finally, we put forward the current challenges and research directions in the field of CPNFs.

Manipulation of Organic Afterglow by Thermodynamic and Kinetic Control

The fabrication of room-temperature organic phosphorescence and afterglow materials, as well as the transformation of their photophysical properties, has emerged as an important topic in the research field of luminescent materials. Here, we report the establishment of energy landscapes in dopant-matrix organic afterglow systems where the aggregation states of luminescent dopants can be controlled by doping concentrations in the matrices and the methods of preparing the materials. Through manipulation by thermodynamic and kinetic control, dopant-matrix afterglow materials with different aggregation states and diverse afterglow properties can be obtained. The conversion from metastable aggregation state to thermodynamic stable aggregation state of the dopant-matrix afterglow materials to leads to the emergence of intriguing afterglow transformation behavior triggered by thermal and solvent annealing. The thermodynamically unfavorable reversible afterglow transformation process can also be achieved by coupling the dopant-matrix afterglow system to mechanical forces.

Propagation-Instigated Self-Limiting Polymerization of Multiarmed Amphiphiles into Finite Supramolecular Polymers

A fundamental goal in the noncovalent synthesis of ordered supramolecular polymers (SPs) is to achieve precise control over their size and size distribution; however, the reversible nature of noncovalent interactions often results in formation of living SPs with high dispersity in length. We report here on the self-limiting supramolecular polymerization (SPZ) of a series of multiarmed amphiphiles with propagation-attenuated reactivities that can automatically terminate the polymerization process, enabling effective control in both lengths and polydispersity. Through incorporating multiarmed oligoethylene-glycol (OEG) onto a quadratic aromatic segment, the lengths of the resultant SPs can be tuned from ∼1 μm to 130 and 50 nm with a polydispersity index of ∼1.2 for the last two SPs. We believe that the level of chain frustration of the multiarmed OEG segments, determined by both the number of arms and the degree of polymerization, poses physical and entropic constrains for supramolecular propagation to exceed a threshold length.

Hierarchical Superstructures by Combining Crystallization-Driven and Molecular Self-Assembly

Combining the unique corona structure of worm-like patchy micelles immobilized on a polymer fiber with the molecular self-assembly of 1,3,5-benzenetricarboxamides (BTAs) leads to hierarchical superstructures with a fir-tree-like morphology. For this purpose, worm-like patchy micelles bearing pendant, functional tertiary amino groups in one of the corona patches were prepared by crystallization-driven self-assembly and immobilized on a supporting polystyrene fiber by coaxial electrospinning. The obtained patchy fibers were then immersed in an aqueous solution of a tertiary amino-functionalized BTA to induce patch-mediated molecular self-assembly to well-defined fir-tree-like superstructures upon solvent evaporation. Interestingly, defined superstructures are obtained only if the pendant functional groups in the surface patches match with the peripheral substituents of the BTA, which is attributed to a local increase in BTA concentration at the polymer fibers' surface.

TADF-Type Organic Afterglow

We report a highly efficient dopant-matrix afterglow system enabled by TADF mechanism to realize afterglow quantum yields of 60-70 %, which features a moderate rate constant for reverse intersystem crossing (k_RISC ) to simultaneously improve afterglow quantum yields and maintain afterglow emission lifetime. Difluoroboron β-diketonate (BF₂ bdk) compounds are designed with multiple electron-donating groups to possess moderate k_RISC values and are selected as luminescent dopants. The matrices with carbonyl functional groups such as phenyl benzoate (PhB) have been found to interact with and perturb BF₂ bdk excited states by dipole-dipole interactions and thus enhance the intersystem crossing of BF₂ bdk excited states. Through dopant-matrix collaboration, the efficient TADF-type afterglow materials have been achieved to exhibit excellent processability into desired shapes and large-area films by melt casting, as well as aqueous afterglow dispersions for potential bioimaging applications.

Exploiting coordination geometry to tune the dimensions and processability of metallosupramolecular polymers

Achieving precise control over the morphology, dimensions and processability of functional materials is a key but challenging requirement for the fabrication of smart devices. To address this issue, we herein compare the self-assembly behavior of two new Pt(ii) complexes that differ in the molecular and coordination geometry through implementation of either a monodentate (pyridine) or bidentate (bipyridine) ligand. The molecular preorganization of the bipyridine-based complex enables effective self-assembly in solution involving Pt⋯Pt interactions, while preserving aggregate solubility. On the other hand, increased steric effects of the linear bispyridine-based complex hinder an effective preorganization leading to poorly solvated aggregates when a critical concentration is exceeded.

Uniform Nanowires Containing a Heterogeneousπ-Conjugated Core of Controlled Length, Composition and Morphology

In this work, it is demonstrated for the first time that heterojunction nanowires, consisting of a gradient and segmented-like heterogeneous π-conjugated core with controllable length, composition and morphology, can be generated by co-self-seeding of oligo(p-phenylene vinylene) (OPV)- and oligo(p-phenylene ethynylene) (OPE)-containing block copolymers in spite of different chain lengths and molecular conformation for OPE and OPV. More importantly, based on the understanding of the formation of heterogeneous core by the co-self-seeding approach, a "heating/cooling" seeded growth route was developed, by which linear and branched heterojunction nanowires containing a segmented heterogeneous π-conjugated core of controlled length, composition and morphology can be obtained. This work provides a versatile platform to generate heterojunction nanowires with excellent controllability in length, composition, and morphology.

Oriented arrangement of simple monomers enabled by confinement: towards living supramolecular polymerization

The living supramolecular polymerization technique provides an exciting research avenue. However, in comparison with the thermodynamic spontaneous nucleation, using simple monomers to realize living supramolecular polymerization is hardly possible from an energy principle. This is because the activation barrier of kinetically trapped simple monomer (nucleation step) is insufficiently high to control the kinetics of subsequent elongation. Here, with the benefit of the confinement from the layered double hydroxide (LDH) nanomaterial, various simple monomers, (such as benzene, naphthalene and pyrene derivatives) successfully form living supramolecular polymer (LSP) with length control and narrow dispersity. The degree of polymerization can reach ~6000. Kinetics studies reveal LDH overcomes a huge energy barrier to inhibit undesired spontaneous nucleation of monomers and disassembly of metastable states. The universality of this strategy will usher exploration into other multifunctional molecules and promote the development of functional LSP.

Using simple monomers in living supramolecular polymerization is difficult due to energy principles. Here the authors use confinement from a layered double hydroxide nanomaterial to successfully polymerise several simple monomers with length control and narrow dispersity.

Recent advances in supramolecular block copolymers for biomedical applications

Supramolecular block copolymers (SBCs) have received considerable interest in polymer chemistry, materials science, biomedical engineering and nanotechnology owing to their unique structural and functional advantages, such as low cytotoxicity, outstanding biodegradability, smart environmental responsiveness, and so forth. SBCs comprise two or more different homopolymer subunits linked by noncovalent bonds, and these polymers, in particular, combine the dynamically reversible nature of supramolecular polymers with the hierarchical microphase-separated structures of block polymers. A rapidly increasing number of publications on the synthesis and applications of SBCs have been reported in recent years; however, a systematic summary of the design, synthesis, properties and applications of SBCs has not been published. To this end, this review provides a brief overview of the recent advances in SBCs and describes the synthesis strategies, properties and functions, and their widespread applications in drug delivery, gene delivery, protein delivery, bioimaging and so on. In this review, we aim to elucidate the general concepts and structure-property relationships of SBCs, as well as their practical bioapplications, shedding further valuable insights into this emerging research field.

Emerging applications for living crystallization-driven self-assembly

The use of crystallization as a tool to control the self-assembly of polymeric and molecular amphiphiles in solution is attracting growing attention for the creation of non-spherical nanoparticles and more complex, hierarchical assemblies. In particular, the seeded growth method termed living crystallization-driven self-assembly (CDSA) has been established as an ambient temperature and potentially scalable platform for the preparation of low dispersity samples of core-shell fiber-like or platelet micellar nanoparticles. Significantly, this method permits predictable control of size, and access to branched and segmented structures where functionality is spatially-defined. Living CDSA operates under kinetic control and shows many analogies with living chain-growth polymerizations of molecular organic monomers that afford well-defined covalent polymers of controlled length except that it covers a much longer length scale (ca. 20 nm to 10 μm). The method has been applied to a rapidly expanding range of crystallizable polymeric amphiphiles, which includes block copolymers and charge-capped homopolymers, to form assemblies with crystalline cores and solvated coronas. Living CDSA seeded growth methods have also been transposed to a wide variety of π-stacking and hydrogen-bonding molecular species that form supramolecular polymers in processes termed "living supramolecular polymerizations". In this article we outline the main features of the living CDSA method and then survey the promising emerging applications for the resulting nanoparticles in fields such as nanomedicine, colloid stabilization, catalysis, optoelectronics, information storage, and surface functionalization.

Solvent-Driven Supramolecular Wrapping of Self-Assembled Structures

Self‐assembly relies on the ability of smaller and discrete entities to spontaneously arrange into more organized systems by means of the structure‐encoded information. Herein, we show that the design of the media can play a role even more important than the chemical design. The media not only determines the self‐assembly pathway at a single‐component level, but in a very narrow solvent composition, a supramolecular homo‐aggregate can be non‐covalently wrapped by a second component that possesses a different crystal lattice. Such a process has been followed in real time by confocal microscopy thanks to the different emission colors of the aggregates formed by two isolated Pt^II complexes. This coating is reversible and controlled by the media composition. Single‐crystal X‐ray diffraction and molecular simulations based on coarse‐grained (CG) models allowed the understanding of the properties displayed by the different aggregates. Such findings could result in a new method to construct hierarchical supramolecular structures.

Synthesis and applications of anisotropic nanoparticles with precisely defined dimensions

Shape and size play powerful roles in determining the properties of a material; controlling these aspects with precision is therefore an important, fundamental goal of the chemical sciences. In particular, the introduction of shape anisotropy at the nanoscale has emerged as a potent way to access new properties and functionality, enabling the exploration of complex nanomaterials across a range of applications. Recent advances in DNA and protein nanotechnology, inorganic crystallization techniques, and precision polymer self-assembly are now enabling unprecedented control over the synthesis of anisotropic nanoparticles with a variety of shapes, encompassing one-dimensional rods, dumbbells and wires, two-dimensional and three-dimensional platelets, rings, polyhedra, stars, and more. This has, in turn, enabled much progress to be made in our understanding of how anisotropy and particle dimensions can be tuned to produce materials with unique and optimized properties. In this Review, we bring these recent developments together to critically appraise the different methods for the bottom-up synthesis of anisotropic nanoparticles enabling exquisite control over morphology and dimensions. We highlight the unique properties of these materials in arenas as diverse as electron transport and biological processing, illustrating how they can be leveraged to produce devices and materials with otherwise inaccessible functionality. By making size and shape our focus, we aim to identify potential synergies between different disciplines and produce a road map for future research in this crucial area.

Achieving Purely-Organic Room-Temperature Aqueous Phosphorescence via a Two-Component Macromolecular Self-Assembly Strategy

Manipulation of supramolecular behaviors and aggregation states represents an important topic in devising intriguing photofunctional systems. Here we report a two-component macromolecular self-assembly strategy for achieving aqueous room-temperature phosphorescence (RTP) in purely organic systems. Amphiphilic triblock copolymers are used to modulate the self-assembly of planar RTP molecules in aqueous solution, leading to the formation of sheet-like RTP objects with well-defined morphology, uniform crystalline nanostructures and excellent aqueous dispersity. In contrast, the addition of the planar RTP molecules into aqueous medium only leads to precipitation and quenching of RTP properties. Powder X-ray diffraction and single-crystal X-ray diffraction studies reveal that the amphiphilic triblock copolymers can assist supramolecular columnar packing of the planar RTP molecules where multiple non-covalent interactions stabilize the triplet excited states. Interestingly, it is found that luminescent signals of the sheet-like RTP objects can be extracted from strong fluorescent environments by phosphorescence mode and emission lifetime measurement.

Platinum(ii) non-covalent crosslinkers for supramolecular DNA hydrogels

Manipulation of non-covalent metal–metal interactions allows the fabrication of functional metallosupramolecular structures with diverse supramolecular behaviors. The majority of reported studies are mostly designed and governed by thermodynamics, with very few examples of metallosupramolecular systems exhibiting intriguing kinetics. Here we report a serendipitous finding of platinum(ii) complexes serving as non-covalent crosslinkers for the fabrication of supramolecular DNA hydrogels. Upon mixing the alkynylplatinum(ii) terpyridine complex with double-stranded DNA in aqueous solution, the platinum(ii) complex molecules are found to first stack into columnar phases by metal–metal and π–π interactions, and then the columnar phases that carry multiple positive charges crosslink the negatively charged DNA strands to form supramolecular hydrogels with luminescence properties and excellent processability. Subsequent platinum(ii) intercalation into DNA competes with the metal–metal and π–π interactions at the crosslinking points, switching on the spontaneous gel-to-sol transition. In the case of a chloro (2,6-bis(benzimidazol-2′-yl)pyridine)platinum(ii) complex, with [Pt(bzimpy)Cl]⁺ serving as a non-covalent crosslinker where the metal–metal and π–π interactions outcompete platinum(ii) intercalation, the intercalation-driven gel-to-sol transition pathway is blocked since the gel state is energetically more favorable than the sol state. Interestingly, the ligand exchange reaction of the chloro ligand in [Pt(bzimpy)Cl]⁺ with glutathione (GSH) has endowed the complexes with enhanced hydrophilicity, decreasing the planarity of the complexes, and turning off the metal–metal and π–π interactions at the crosslinking points, leading to GSH-triggered hydrogel dissociation.

We report a serendipitous finding of platinum(ii) complexes serving as non-covalent crosslinkers for the fabrication of supramolecular DNA hydrogels.

Platinum(II) Probes for Sensing Polyelectrolyte Lengths and Architectures

Platinum(II) polypyridine complexes of a square-planar geometry have been used as spectroscopic reporters for quantification of various charged species through non-covalent metal-metal interactions. The characterization of molecular weights and architectures of polyelectrolytes represents a challenging task in polymer science. Here, we report the utilization of platinum(II) complex probes and non-covalent metal-metal interactions for sensing polyelectrolyte lengths and architectures. It is found that the platinum(II) probes can bind to linear polyelectrolytes via electrostatic attractions and give rise to significant spectroscopic changes associated with the formation of metal-metal interactions, and the extent of the spectroscopic changes is found to increase with the lengths of the linear polyelectrolytes. Besides, the platinum(II) probes have been found to co-assemble with the linear polyelectrolytes to form well-defined nanofibers, and the lengths of the linear polyelectrolytes can be directly estimated from the diameter of the nanofibers under transmission electron microscopy observation. Interestingly, upon mixing with the platinum(II) probes, polyelectrolytes with bottlebrush architectures have been found to exhibit larger spectroscopic changes than linear polyelectrolytes with the same chemical composition. Combined with the reported theoretical studies on counterion condensation of polyelectrolytes, the platinum(II) complexes are found to function as spectroscopic probes for sensing the charge densities of the polyelectrolytes with different lengths and diverse architectures. Moreover, platinum(II) probes pre-organized in nanostructured aggregates have been found to intercalate into double-stranded DNA, which are naturally occurring biological polyelectrolytes with helical architectures and intercalation sites, to give significant enhancement of spectroscopic changes when compared to the intercalation of monomeric platinum(II) probes into double-stranded DNA.

Controlled supramolecular polymerization of π-systems

Externally-initiated controlled supramolecular polymerization of the kinetically trapped aggregated state in a chain growth mechanism can produce well-defined living supramolecular polymers and copolymers.

A guide to supramolecular polymerizations

Supramolecular polymers are non-covalent assemblies of unimeric building blocks connected by secondary interactions and hold great promises due to their dynamic nature.

Anisotropic polymer nanoparticles with controlled dimensions from the morphological transformation of isotropic seeds

Understanding and controlling self-assembly processes at multiple length scales is vital if we are to design and create advanced materials. In particular, our ability to organise matter on the nanoscale has advanced considerably, but still lags far behind our skill in manipulating individual molecules. New tools allowing controlled nanoscale assembly are sorely needed, as well as the physical understanding of how they work. Here, we report such a method for the production of highly anisotropic nanoparticles with controlled dimensions based on a morphological transformation process (MORPH, for short) driven by the formation of supramolecular bonds. We present a minimal physical model for MORPH that suggests a general mechanism which is potentially applicable to a large number of polymer/nanoparticle systems. We envision MORPH becoming a valuable tool for controlling nanoscale self-assembly, and for the production of functional nanostructures for diverse applications.

Exploiting Coordination Isomerism for Controlled Self-Assembly

We exploited the inherent geometrical isomerism of a PtII complex as a new tool to control supramolecular assembly processes. UV irradiation and careful selection of solvent, temperature, and concentration leads to tunable coordination isomerism, which in turn allows fully reversible switching between two distinct aggregate species (1D fibers↔2D lamellae) with different photoresponsive behavior. Our findings not only broaden the scope of coordination isomerism, but also open up exciting possibilities for the development of novel stimuli-responsive nanomaterials.

One-shot preparation of topologically chimeric nanofibers via a gradient supramolecular copolymerization

Supramolecular polymers have emerged in the last decade as highly accessible polymeric nanomaterials. An important step toward finely designed nanomaterials with versatile functions, such as those of natural proteins, is intricate topological control over their main chains. Herein, we report the facile one-shot preparation of supramolecular copolymers involving segregated secondary structures. By cooling non-polar solutions containing two monomers that individually afford helically folded and linearly extended secondary structures, we obtain unique nanofibers with coexisting distinct secondary structures. A spectroscopic analysis of the formation process of such topologically chimeric fibers reveals that the monomer composition varies gradually during the polymerization due to the formation of heteromeric hydrogen-bonded intermediates. We further demonstrate the folding of these chimeric fibers by light-induced deformation of the linearly extended segments.

Detailed Approach to Investigate Thermodynamically Controlled Supramolecular Copolymerizations

Elucidating the microstructure of supramolecular copolymers remains challenging, despite the progress in the field of supramolecular polymers. In this work, we present a detailed approach to investigate supramolecular copolymerizations under thermodynamic control. Our approach provides insight into the interactions of different types of monomers and hereby allows elucidating the microstructure of copolymers. We select two monomers that undergo cooperative supramolecular polymerization by way of threefold intermolecular hydrogen bonding in a helical manner, namely, benzene-1,3,5-tricarboxamide (BTA) and benzene-1,3,5-tris(carbothioamide) (thioBTA). Two enantiomeric forms and an achiral analogue of BTA and thioBTA are synthesized and their homo- and copolymerizations are studied using light scattering techniques, infrared, ultraviolet, and circular dichroism spectroscopy. After quantifying the thermodynamic parameters describing the homopolymerizations, we outline a method to follow the self-assembly of thioBTA derivatives in the copolymerization with BTA, which involves monitoring a characteristic spectroscopic signature as a function of temperature and relative concentration. Using modified types of sergeants-and-soldiers and majority-rules experiments, we obtain insights into the degree of aggregation and the net helicity. In addition, we apply a theoretical model of supramolecular copolymerization to substantiate the experimental results. We find that the model describes the two-component system well and allows deriving the hetero-interaction energies. The interactions between the same kinds of monomers (BTA-BTA and thioBTA-thioBTA) are slightly more favorable than those between different monomers (BTA-thioBTA), corresponding to a nearly random copolymerization. Finally, to study the interactions of the monomers at the molecular level, we perform density functional theory-based computations. The results corroborate that the two-component system exhibits a random distribution of the two monomer units along the copolymer chain.

Steering the Self-Assembly Outcome of a Single NDI Monomer into Three Morphologically Distinct Supramolecular Assemblies, with Concomitant Change in Supramolecular Polymerization Mechanism

Noncovalent self-assembly creates an effective route to highly sophisticated supramolecular polymers with tunable properties. However, the outcome of this assembly process is highly dependent on external conditions. In this work, a monomeric naphthalene diimide (NDI), designed to allow solubility in a wide range of solvents, can assemble into three distinct noncovalent supramolecular species depending on solvent composition and temperature. Namely, while the self-assembly in chlorinated solvents yields relatively short, hydrogen-bonded nanotubes, the reduction of solvent polarity changes the assembly outcome, yielding π-π stacking polymers, which can further bundle into a more complex aggregate. The obtained polymers differ not only in their global morphology but-more strikingly-also in the thermodynamics and kinetics of their supramolecular self-assembly, involving isodesmic or two-stage cooperative assembly with kinetic hysteresis, respectively. Ultimately, three distinct assembly states can be accessed in a single experiment.

Supramolecular Block Copolymers by Seeded Living Polymerization of Perylene Bisimides

Living covalent polymerization has been a subject of intense research for many decades and has culminated in the synthesis of a large variety of block copolymers (BCPs) with structural and functional diversity. In contrast, the research on supramolecular BCPs is still in its infancy and their generation by living processes remains a challenge. Here we report the formation of supramolecular block copolymers by two-component seeded living polymerization of properly designed perylene bisimides (PBIs) under precise kinetic control. Our detailed studies on thermodynamically and kinetically controlled supramolecular polymerization of three investigated PBIs, which contain hydrogen-bonding amide side groups in imide position and chlorine, methoxy, or methylthio substituents in 1,7 bay-positions, revealed that these PBIs form kinetically metastable H-aggregates, which can be transformed into the thermodynamically favored J-aggregates by seed-induced living polymerization. We show here that copolymerization of kinetically trapped states of one PBI with seeds of another PBI leads to the formation of supramolecular block copolymers by chain-growth process from the seed termini as confirmed by UV/vis spectroscopy and atomic force microscopy (AFM). This work demonstrates for the first time the formation of triblock supramolecular polymer architectures with A-B-A and B-A-B block pattern by alternate two-component seeded polymerization in a living manner.