Cooperative supramolecular polymerization of an amine-substituted naphthalene-diimide and its impact on excited state photophysical properties

A donor-acceptor-donor (D-A-D) type naphthalene-diimide (NDI-H) chromophore exhibits highly cooperative J-aggregation leading to nanotubular self-assembly and gelation in n-decane, as demonstrated by UV/Vis, FT-IR, photoluminescence and microscopy studies. Analysis of temperature-dependent UV/Vis spectra using the nucleation-elongation model and FT-IR data reveals the molecular origin of the cooperative nature of the self-assembly. The supramolecular polymerization is initiated by H-bonding up to a degree of polymerization similar to 20-25, which in a subsequent elongation step promotes J-aggregation in orthogonal direction leading to possibly a sheet-like structure that eventually produces nanotubes. Time-resolved fluorescence and absorption measurements demonstrate that such a tubular assembly enables very effective delocalization of excited states resulting in a remarkably prolonged excited state lifetime

Influence of Metal, Ligand and Solvent on Supramolecular Polymerizations with Transition-Metal Compounds: A Theoretical Study

The nature of intermolecular interactions governing supramolecular polymerizations is very important to control their cooperativity. In order to address this problem, supramolecular columns made of Pt(II) and Pd(II) complexes of oligo(phenyleneethynylene)-based pyridine (OPE) and tetrazolyl-pyridine ligands (TEP) were investigated through the dispersion-corrected PM6 method. Aromatic, CH-π, M-Cl and metallophilic interactions helped stabilize the supramolecules studied, and their geometries and associated cooperativities were in excellent agreement with experimental data. The OPE ligand and/or the presence of Pt(II) have led to stronger metallophilic interactions and also to cooperative supramolecular polymerizations, which clearly suggests that metallophilic interactions are a key factor to control cooperativity. The results indicate that sequential monomer addition is in general less spontaneous than the combination of two larger pre-formed stacks. The present theoretical investigations contribute to the further understanding of the relation between the thermodynamics of supramolecular polymerizations and the nature of different synthons

Control over the Self-Assembly Modes of Pt^II Complexes by Alkyl Chain Variation: From Slipped to Parallel π-Stacks

We report the self-assembly of a new family of hydrophobic, bis(pyridyl) PtII complexes featuring an extended oligophenyleneethynylene-derived π-surface appended with six long (dodecyloxy (2)) or short (methoxy (3)) side groups. Complex 2, containing dodecyloxy chains, forms fibrous assemblies with a slipped arrangement of the monomer units (dPt⋯Pt≈14 Å) in both nonpolar solvents and the solid state. Dispersion-corrected PM6 calculations suggest that this organization is driven by cooperative π-π, C-H⋯Cl and π-Pt interactions, which is supported by EXAFS and 2D NMR spectroscopic analysis. In contrast, nearly parallel π-stacks (dPt⋯Pt≈4.4 Å) stabilized by multiple π-π and C-H⋯Cl contacts are obtained in the crystalline state for 3 lacking long side chains, as shown by X-ray analysis and PM6 calculations. Our results reveal not only the key role of alkyl chain length in controlling self-assembly modes but also show the relevance of Pt-bound chlorine ligands as new supramolecular synthons. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Self-Assembly of 9,10-Bis(phenylethynyl) anthracene (BPEA) Derivatives: Influence of pi-pi and Hydrogen Bonding Interactions on Aggregate Morphology and Self-Assembly Mechanism

9,10-Bis(phenylethynyl)anthracenes (BPEAs) are an important class of dyes with various applications including chemiluminescence emitters, materials for photon upconversion and for optoelectronic devices. Some of these applications require control over the packing modes of the active molecules within the active layer, which can be effected by bottom-up self-assembly. Studies aimed at controlling the molecular organization of BPEAs have primarily focused on bulk or liquid crystal materials, while in-depth investigations of BPEA-based assemblies in solution remain elusive. In this article, we report the self-assembly of two new BPEA derivatives with hydrophobic side chains, one of them featuring amide functional groups (2) and the other one lacking them (1). Comparison of the self-assembly behaviour in solution of both systems via spectroscopic (UV/Vis, fluorescence and NMR), microscopic (AFM) and theoretical (PM6) studies reveals the crucial role of the amide groups in controlling the self-assembly. While for both systems the formation of H-type face-to-face -stacks is proposed, the interplay of -stacking and H-bonding is responsible of driving the formation of 1D stacks and increasing the binding constant two-to-three orders of magnitude. Our findings show that H-bonding is a prerequisite to create ordered BPEA assemblies in solution

Influence of metal coordination and light irradiation on hierarchical self-assembly processes

Smart light-responsive supramolecular materials have been extensively investigated in the past decade, but so far the impact of metal coordination on hierarchical supramolecular structures of light-responsive building blocks has remained nearly unexplored. Herein, we unravel the hierarchical self-assembly of a small π-conjugated azo-containing pyridyl ligand that is able to respond to UV-light and metal complexation. The ligand self-assembles in an antiparallel fashion into long twisted fibers, which are then disassembled upon photoisomerization of the azobenzene groups, resulting in shorter rigid rods with a different packing motif. Complexation of Pd(ii) ions enhances the cooperativity of the aggregation and induces a molecular rearrangement into slipped stacks with subsequent formation of long thin fibers. These are then transformed into thinner, shorter rods upon light irradiation. The observed different light-responsiveness, besides clearing up the influence of metal coordination and light irradiation in self-assembly processes, paves the way towards the design of novel supramolecular photochromic systems. © 2019 The Royal Society of Chemistry

Luminescent gels by self-assembling platinum complexes

A platinum complex bearing a tetraethylene glycol chain has been designed and its self-assembly properties investigated. In solution, only a yellow phosphorescence of the aggregated species is observed. The complex gives luminescent gels of different colours with DCM and DMF, reaching up to 60% photoluminescence quantum yield. \ua9 2012 The Royal Society of Chemistry

Tuning the structural and photophysical properties of cationic Pt(II) complexes bearing neutral bis(triazolyl)pyridine ligands

The emission properties of a series of cationic Pt(II) complexes bearing neutral tridentate 2,6-bis-(1H-1,2,3-triazol-5-yl)pyridine and monoanionic ancillary ligands (Cl- or CN-) are described. By varying the substitution pattern on the 1,2,3-triazole moieties of the tridentate luminophore and the nature of the ancillary ligand, we were able to tune the intermolecular interactions between the complexes and therefore the electronic interactions between the metal centers. Indeed, all the compounds possessing Cl- as ancillary ligand are nonluminescent at room temperature, while the complexes containing CN- are luminescent. Interestingly, the \u3c0-accepting nature of this ancillary ligand induces Pt(II)-Pt(II) interactions irrespectively of bulky substitution patterns on the tridentate ligand

Kontrolle über Selbstassemblierung durch Ausnutzung von Koordinationsisomerie

Hierin wird die inhärente geometrische Isomerie eines PtII Komplexes als neues Werkzeug zur Kontrolle von supramolekularen Assemblierungsprozessen ausgenutzt. Bestrahlung mit UV‐Licht sowie die sorgfältige Auswahl des verwendeten Lösungsmittels, der Temperatur und Konzentration führen zu einer regelbaren Koordinationsisomerie. Dies ermöglicht ein vollständig reversibles Schalten zwischen zwei definierten aggregierten Spezies (1D Fasern ↔ 2D Lamellen) mit unterschiedlichem photoresponsivem Verhalten. Unsere Erkenntnisse erweitern nicht nur die Reichweite von Koordinationsisomerie, sondern eröffnen auch aufregende Möglichkeiten zur Entwicklung neuartiger stimuliresponsiver Materialien

Mechanistische Einblicke in die Selbstorganisation eines säure-empfindlichen photoresponsiven supramolekularen Polymers

The supramolecular polymerization of an acid-sensitive pyridyl-based ligand (L1) bearing a photoresponsive azobenzene moiety was elucidated by mechanistic studies. Addition of trifluoroacetic acid (TFA) led to the transformation of the antiparallel H-bonded fibers of L1 in methylcyclohexane into superhelical braid-like fibers stabilized by H-bonding dimers held together by unconventional pyridine–TFA N···H···O bridges represent the main structural elements of the assembly. UV-light irradiation caused a strain-driven disassembly and subsequent aggregate reconstruction, which ultimately led to short fibers. The results allowed to understand the mechanism of mutual influence of acid and light stimuli on supramolecular polymerization processes, thus opening up new possibilities to design advanced stimulitriggered supramolecular systems