ADMET Polycondensation of Diketopiperazine-Based Dienes. Polymerization Behavior and Effect of Diketopiperazine on the Properties of the Formed Polymers

Metal-Assisted Synthesis of Extended Polyaromatic Nitrogen-Rich Ligands for Tunable Sensitization of Eu(III) Complexes

We report the metal-assisted synthesis of oligomeric nitrogen-rich DiL1 and PoL1n sensitizers from the monomer L1 via acyclic diene metathesis (ADMET) polymerization for the tuning of the photoluminescence properties of europium-containing complexes by ligand design. The binding of [Eu(hfac)3] cargoes (H-hfac = 1,1,1,5,5,5-hexafluoropentane-2,4-dione) to monomer L1 to give [L1Eu(hfac)3] during metathesis appeared to be essential (i) for protecting the Grubbs ruthenium catalyst to interact with the nitrogen atoms of L1 and (ii) to drive the Ru-catalyzed ADMET reaction toward dimeric {DiL1[Eu(hfac)3]2} and polymeric {PoL1n[Eu(hfac)3]n} assemblies. Compared with the monomeric tridentate L1-L4 ligands, significant electronic delocalization occurs through the π-conjugated benzimidazole-CH═CH-benzimidazole skeletons in the dimer DiL1 and polymers PoL1n, which results in a stepwise red-shift of the excited levels in these extended polyaromatic ligands. As a consequence, the sensitization of bound [Eu(hfac)3] units reveals a decrease of the photoluminescence quantum yields along the [L4Eu(hfac)3] > [L3Eu(hfac)3] > [L2Eu(hfac)3] ≈ [L1Eu(hfac)3] > {DiL1[Eu(hfac)3]2} > {PoL118[Eu(hfac)3]18} series due to unfavorable europium-to-ligand back energy transfers.

Tyrosine-based photoluminescent diketopiperazine supramolecular aggregates

L-Tyrosine diketopiperazine (DKP) derivative 1 was synthesized, and the aggregation and photoluminescence behaviors were examined. A solution of 1 in tetrahydrofuran (THF) gradually became viscous at room temperature, and turned into the gel state 5 hours after preparation, as confirmed by dynamic viscoelasticity measurement. A solution of 1 in THF exhibited photoluminescence. Fibrous patterns were observed by transmission electron, atomic force and fluorescence microscopies. Dynamic light scattering, semiempirical molecular orbital and density functional theory calculations, as well as molecular dynamics simulations, indicated aggregate formation. This was attributed to intermolecular hydrogen bonding, mainly between the DKP moieties and partly between the urethane moieties, resulting in π-orbital overlap of the terminal phenyl groups leading to photoluminescence.

Synthesis and solvent-controlled self-assembly of diketopiperazine-based polyamides from aspartame

An aspartame-based AB-type diketopiperazine monomer, cyclo(l-aspartyl-4-amino-l-phenylalanyl) (ADKP), was synthesized and subsequently utilized in the polycondensation of homo-polyamides with high molecular weights. By using various amino acids, dicarboxylic acids, and diamines, random DKP-based copolymers were also synthesized. The self-assembly properties of ADKP and poly(cyclo(l-aspartyl-4-amino-l-phenylalanyl)) (PA1) were studied via the solvent displacement method. Notably, PA1 self-assembled into particles with various morphologies in different solvent systems, such as irregular networks, ellipsoids, and hollow particles. The morphological transformation was also confirmed by dropping acetone and toluene onto the PA1 particles. Furthermore, infrared spectra and Hansen solubility parameters of PA1 and different solvents revealed the particle formation mechanism, which provided more insights into the relationship between the morphology and strength of the hydrogen bonding of each solvent.

Diketopiperazine-based polyamides have been synthesized from aspartame, and could self-assemble into particles with various morphologies in different solvents.

Morphology-Controlled Self-Assembly and Synthesis of Biopolyimide Particles from 4-Amino-l-phenylalanine

Self-assembling polyimides (PIs) having diketopiperazine (DKP) components were synthesized by polycondensation of a 4-amino-l-phenylalanine (4APhe) dimer, an aromatic diamine newly designed in this study. The amino acid-derived PIs showed high thermal resistance, with a 10% weight loss temperature (T _d10) of 432 °C at the maximum, and did not show any glass transition below the thermal decomposition temperature. The poly(amic acid) (PAA) precursors formed nanospheres upon reprecipitation over dimethylacetamide into water. The nanospheres were then added to solvents with different polarities and sonicated to induce deformation of the spherical forms into spiky balls, flakes, or rods. The PAA particle morphologies were retained in the PIs after the two-step imidization. Finally, the PI particles with self-assembling DKP moieties were formed, and their morphologies were fine-tuned using different mixed solvents.

Polymerization of cystine-derived monomers

Platform of cystine-derived acyclic and cyclic monomers for step-growth and entropy-driven ring-opening polymerization.

Functional Precision Polymers via Stereo- and Regioselective Polymerization Using Group 6 Metal Alkylidene and Group 6 and 8 Metal Alkylidene N-Heterocyclic Carbene Complexes

The concepts of functional precision polymers and the latest accomplishments in their synthesis are summarized. Synthetic concepts based on chain growth polymerization are compared to iterative synthetic approaches. Here, the term "functional precision polymers" refers to polymers that are not solely hydrocarbon-based but contain functional groups and are characterized by a highly ordered primary structure. If insertion polymerization is used for their synthesis, olefin metathesis-based polymerization techniques, that is, ring-opening metathesis polymerization (ROMP), acyclic diene metathesis (ADMET) polymerization, and the regio- and stereoselective cyclopolymerization of α,ω-diynes are almost exclusively applied. Particularly with regio- and stereospecific ROMP and with cyclopolymerization, the synthesis of tactic polymers and copolymers with high regio-, stereo-, and sequence control can be accomplished; however, it requires carefully tailored transition metal catalysts. The fundamental synthetic concepts and strategies are outlined.

Metathesis polymerization of cystine-based macrocycles

Entropy-driven ring-opening metathesis polymerization (ED-ROMP) of cystine-based macrocycles yields multifunctional poly(ester-amine-disulfide-alkene)s.

Single-chain nanoparticles containing sequence-defined segments: using primary structure control to promote secondary and tertiary structures in synthetic protein mimics

We investigated intra-chain multicomponent reactions to synthesize single-chain nanoparticles (SCNP) containing sequence-defined segments at each cross-link, creating materials featuring multiple protein-inspired elements.

One-pot oligoamides syntheses from l-lysine and l-tartaric acid

Oligoamides based on natural raw materials, l-lysine and l-tartaric acid, were synthesized using one-pot processes. A l-lysine diketopiperazine structure was obtained with good selectivity without protection/deprotection steps.

Green chain-shattering polymers based on a self-immolative azobenzene motif

A chain-shattering polymer system consisting of nontoxic, partially renewable resource-based monomersviaacyclic diene metathesis (ADMET) chemistry is introduced.

Functional α,ω-dienes via thiol-Michael chemistry: synthesis, oxidative protection, acyclic diene metathesis (ADMET) polymerization and radical thiol–ene modification

The synthesis of the novel α,ω-diene 2-(undec-10-en-1-yl)tridec-12-en-1-yl acrylate is described.