Reading the bands: Amphiphilic pyrene trimers self-assemble into two-dimensional, supramolecular polymers in aqueous medium. Folding and aggregation processes are accompanied by simultaneous development of J- and H-bands and significant changes in the fluorescence properties. The formation of sheet-like nano-structures is confirmed by AFM.

The precise arraying of functional entities in a reproducible and predictable way in morphologically well-defined shapes is a key challenge in materials science. In this work, we describe the importance of kinetic effects in the two-dimensional (2D) self-assembly of a negatively charged pyrene trimer (Py 3 ) in aqueous media. Under optimized experimental conditions the chain-folded oligomers assemble into exceptionally thin planar assemblies (∼2 nm thick) with a very high aspect ratio (area/thickness ratio ≈ 107 nm). The morphology of the nanosheets was characterized by different microscopic techniques (AFM, TEM, and optical microscopy), while UV-vis and fluorescence spectroscopy revealed details on the intramolecular folding of the oligomer strands. Temperature control was shown to be crucial for preventing the formation of kinetically trapped states, thus allowing the development of extra-large 2D assemblies.

The controlled arraying of DNA strands on adaptive polymeric platforms remains a challenge. Here, the noncovalent synthesis of DNA-grafted supramolecular polymers from short chimeric oligomers is presented. The oligomers are composed of an oligopyrenotide strand attached to the 5'-end of an oligodeoxynucleotide. The supramolecular polymerization of these oligomers in an aqueous medium leads to the formation of one-dimensional (1D) helical ribbon structures. Atomic force and transmission electron microscopy show rod-like polymers of several hundred nanometers in length. DNA-grafted polymers of the type described herein will serve as models for the development of structurally and functionally diverse supramolecular platforms with applications in materials science and diagnostics.

DNA-grafted supramolecular polymers (SPs) allow the programmed organization of DNA in a highly regular, one-dimensional array. Oligonucleotides are arranged along the edges of pyrene-based helical polymers. Addition of complementary oligonucleotides triggers the assembly of individual nanoribbons resulting in the formation of extended supramolecular networks. Network formation is enabled by cooperative coaxial stacking interactions of terminal GC base pairs. The process is accompanied by structural changes in the pyrene polymer core that can be followed spectroscopically. Network formation is reversible and disassembly into individual ribbons is realized either via thermal denaturation or by addition of a DNA separator strand.The creation of functional nanoscale structures represents a major goal of today's nanotechnology. DNA-based materials are of primary interest for the construction of functional platforms. [1][2][3][4] Proper choice of the nucleotide sequence provides control over aromatic stacking and hydrogen bonding interactions, 5-7 thus enabling the assembly of systems with a high degree of complexity. [8][9][10][11] Approaches towards the preparation of functional DNA materials include the designed DNA self-assembly, 12-15 the grafting of oligonucleotides onto metal nanoparticles (NPs) 16 and other surfaces, [17][18][19] as well as polymers. [20][21][22][23] The latter class, DNA-grafted polymers, has been pioneered by Nguyen and Mirkin and gained increasing attention over the last years. 24,25 We have recently introduced DNA-grafted supramolecular polymers (SPs). 26 These self-assembled structures appear as one-dimensional (1D) ribbons, consisting of an oligopyrenotide core 27 with arrays of singlestranded oligonucleotides appended onto its edges. The non-covalent nature of SPs brings the additional feature of reversibility of the polymerization process. [28][29][30][31][32][33][34] Furthermore, it enables the formation of polymers with a high DNA grafting density. 25,26 Herein we describe the hierarchical organization of DNA-grafted SPs. It is shown that individual ribbons assemble into extended networks through a highly cooperative mesh of DNA blunt end stacking interactions.Chimeric oligomers Py-a, Py-b and Py-c (Scheme 1) are all composed of a heptapyrenotide part and an appended oligonucleotide.They were prepared via solid-phase synthesis, purified by RP-HPLC and characterized by MS (SI). The two complementary oligonucleotides 1a (separator strand) and 1b (connector strand) have the same nucleobase sequence as the respective corresponding chimeric oligomers Py-a and Py-b; 1c is complementary to the oligonucleotide part of Py-c. DNA-grafted SPs are typically performed by slow annealing. Thus, a 2 μM solution of Py-a in aqueous buffer (10 mM sodium phosphate, pH=7.0 and 250 mM sodium chloride) is cooled from 95° to 20°C using a gradient of 0.1°C/min. Stacking interactions between pyrenes drive the self-assembly of polymeric ribbons. The polymerization process leads to the development ...

Replacement of the natural nucleotides in DNA by non-nucleosidic building blocks leads to phosphodiester-linked oligomers with a high functional diversity.

The synthesis, characterization and functionalization of DNA-grafted supramolecular polymers are described. Cargo loading of the helical supramolecular assemblies with gold nanoparticles is demonstrated.

Double stranded DNA hybrids containing up to four consecutive, face-to-face stacked porphyrins are described. Non-nucleosidic, 5,15-bisphenyl-substituted porphyrin building blocks were incorporated into complementary oligonucleotide strands. Upon hybridization multiple porphyrins are well accommodated inside the DNA scaffold without disturbing the overall B-DNA structure. The formation of double strands containing up to four free base porphyrins is enabled without compromising duplex stability. UV/vis, fluorescence, and CD spectroscopy demonstrate the formation of porphyrins H-aggregates inside the DNA double helix and provide evidence for the existence of strong excitonic coupling between interstrand stacked porphyrins. H-aggregation results in considerable fluorescence quenching. Most intense CD effects are observed in stacks containing four porphyrins. The findings demonstrate the value of DNA for the controlled formation of molecularly defined porphyrin aggregates.

The self-assembly of an amphiphilic 2,7-linked pyrene trimer in an aqueous environment into two morphologically related forms is described. Supramolecular polymerization leads to the simultaneous formation of nanosheets and nanotubes.