Probing the Analogy between Living Crystallization-Driven Self-Assembly and Living Covalent Polymerizations: Length-Independent Growth Behavior for 1D Block Copolymer Nanofibers

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.

Impact of Hydrophobic/Hydrophilic Balance on Aggregation Pathways, Morphologies, and Excited-State Dynamics of Amphiphilic Diketopyrrolopyrrole Dyes in Aqueous Media

We report the thermodynamic and kinetic aqueous self-assembly of a series of amide-functionalized dithienyldiketopyrrolopyrroles (TDPPs) that bear various hydrophilic oligoethylene glycol (OEG) and hydrophobic alkyl chains. Spectroscopic and microscopic studies showed that the TDPP-based amphiphiles with an octyl group form sheet-like aggregates with J-type exciton coupling. The effect of the alkyl chains on the aggregated structure and the internal molecular orientation was examined via computational studies combining MD simulations and TD-DFT calculations. Furthermore, solvent and thermal denaturation experiments provided a state diagram that indicates the formation of unexpected nanoparticles during the self-assembly into nanosheets when longer OEG side chains are introduced. A kinetic analysis revealed that the nanoparticles were obtained selectively as an on-pathway intermediate state toward the formation of thermodynamically controlled nanosheets. The metastable aggregates were used for seed-initiated supramolecular assembly, which allowed establishing control over the assembly kinetics and the aggregate size. The sheet-like aggregates prepared using the seeding method exhibited coherent vibration in the excited state, indicating a well-ordered orientation of the TDPP units. These results underline the significance of fine tuning of the hydrophobic/hydrophilic balance in the molecular design to kinetically control the assembly of amphiphilic π-conjugated molecules into two-dimensional nanostructures in aqueous media.

AIE-Active, Stimuli-Responsive Fluorescent 2D Block Copolymer Nanoplatelets Based on Corona Chain Compression

Aggregation-induced emission (AIE) represents a powerful tool in nanoscience as a result of enhanced luminescence in the condensed state. Although AIEgenic materials have been utilized in a wide range of applications, well-defined self-assembled nanoparticles with tailorable and uniform dimensions and morphology remain challenging to access. Herein, we use the seeded growth, living crystallization-driven self-assembly (CDSA) method to prepare size-tunable and uniform AIE-active 2D nanoplatelets from amphiphilic block copolymer (BCP) precursors with a crystallizable core-forming block and a corona-forming block to which tetraphenylethene (TPE) groups were covalently grafted as AIE-active pendants. The nanoplatelets were formed as a result of a solvophobicity-induced 1D to 2D morphology preference change, which accompanied the seeded growth of a BCP with a quaternized corona-forming block bearing the TPE luminogen. The 2D nanoplatelets exhibited a solvent-responsive fluorescent emission, and examples with coronas containing homogeneously distributed AIE-active TPE groups and Hg(II)-capturing thymine units exhibited excellent performance as proof-of-concept "turn-on" sensors for Hg(II) detection with a rapid response, high selectivity, and a low detection limit (5-125 × 10^-9 M, i.e., 1-25 ppb). The fluorescence intensity was found to be nonlinear with respect to analyte concentration and to increase with the area of the nanoplatelet. This behavior is consistent with a cooperative mechanism based on changes in the steric compression of the corona chains, which gives rise to a restriction of the intramolecular motion (RIM) effect.