Recently developed chain walking (CW) catalysis is an elegant approach to produce materials with controllable structure and properties. However, there is still a lack in understanding of how the reaction mechanism influences the macromolecular structures. In this study, a series of dendritic polyethylenes (PE) synthesized by Pd-α-diimine-complex through CW catalysis (CWPE) is investigated by means of theory and experiment. Thereby, the exceptional ability of in situ tailoring polymer structure by varying synthesis parameters was exploited to tune the branching architecture, which allowed us to establish a precise relationship between synthesis, structure, and solution properties. The systematically produced polymers were characterized by state-of-the-art multidetector separation and neutron scattering experiments as well as atomic force microscopy to access molecular properties of CWPE. On a global scale, the CWPE appear in a worm-like conformation independently on the synthesis conditions. However, severe differences in their contraction factors suggested that CWPE differ substantially in topology. These observations were verified by NMR studies that showed that CWPE possess a constant total number of branches but varying branching distribution. Small angle neutron scattering experiments gave access to structural characteristics from global to segmental scale and revealed the unique heterogeneity of CWPE, which is predominantly based on differences in their dendritic side chains. The experimental data were compared to theoretical CW structures modeled with different reaction-to-walking probabilities. Simple theoretical arguments predict a crossover from dendritic to linear topologies yielding a structural range from purely linear to dendritic chain growth. Yet, comparison of theoretical and empirical scattering curves gave the first evidence that a transition state to worm-like topologies is actually experimentally accessible. This crossover regime is characterized by linear global features and dendritic local substructures contrary to randomly hyperbranched systems. Instead, the obtained CWPE systems have characteristics of disordered dendritic bottle brushes and can be adjusted by the walking rate/reaction probability of the catalyst.

A novel approach for the integration of π-conjugated polymers (CPs) into DNA-based nanostructures is presented. Using the controlled Kumada catalyst-transfer polycondensation, well-defined thiophene-based polymers with controllable molecular weight, specific end groups, and water-soluble oligoethylene glycol-based side chains were synthesized. The end groups were used for the easy but highly efficient click chemistry-based attachment of end-functionalized oligodeoxynucleotides (ODNs) with predesigned sequences. As demonstrated by surface plasmon resonance spectroscopy, the prepared block copolymers (BCPs), P3(EO)T-b-ODN, comprising different ODN lengths and specific or repetitive sequences, undergo specific hybridization with complementary, thiol-functionalized ODNs immobilized on a gold surface. Furthermore, the site-specific attachment of the BCPs to DNA origami structures is studied. We demonstrate that a nanoscale object, that is, a single BCP with a single ODN handle, can be directed and bound to the DNA origami with reasonable yield, site-specificity, and high spatial density. On the basis of these results, we are able to demonstrate for the first time that optical properties of CP molecules densely immobilized on DNA origami can be locally fine-tuned by controlling the attractive π-π-stacking interactions between the CPs. In particular, we show that the fluorescence of the immobilized CP molecules can be significantly enhanced by surfactant-induced breakup of π-π-stacking interactions between the CP's backbones. Such molecular control over the emission intensity of the CPs can be valuable for the construction of sophisticated switchable nanophotonic devices and nanoscale biosensors.

respond to mechanical stress with a change of their absorption and fluorescence features, [1][2][3] have been previously considered to monitor the material's failure. A clear color-shift, which requires a shift in the absorption band, would provide a fast, visible warning sign for mechanical stress or deformations in the material. Moreover, mechanochromic polymers might be useful in many emerging materials and applications, e.g., in artificial skin, wearable, camouflage systems, and attoreactor sensors, and for anti-counterfeiting. [4][5][6][7][8][9] There are two major approaches to build up polymer-based mechanochromic materials. The first is the incorporation of so-called aggregachromic dyes into polymer matrixes to form thermodynamically stable micro-/nano-sized aggregates. [6,10] Aggregachromic dyes are planar, rigid π-conjugated small molecules, which form J-or H-aggregates through the π-stacking interactions and exhibit distinct optical properties as compared to the monomeric species (bathochromically or hypsochromically shifted absorptions/emissions). The second approach involves a covalent linking of chromogenic units to polymer chains. [11,12] The colorimetric transition can originate from changing molecular interactions, e.g., aggregation, [6,13] or caused by chemical transformations. [11,14,15] Common chromogenic units are organic molecules [16] or organometallic complexes. [17,18] The use of π-conjugated polymers (CPs) as chromogenic units is rare and mainly based on the cis-trans isomerization of acetylene derivatives. [19][20][21][22] One of the most abundant mechanisms responsible for the mechanochromism is the aggregation-induced change of the material optical properties (absorption and/or fluorescence) on the response of the mechanical stress. [10,23,24] For such systems to perform properly, the active chromophore should be evenly distributed in the matrix and be present at substantial amounts, around a critical aggregation concentration (typically in 0.1-1% range), which is not always convenient and cheap.We propose CPs as interesting alternative to aggregachromic dyes for mechanochromic materials. Due to their extended π-conjugated systems along their polymer backbone, CPs possess a strong absorption and luminescence in the visible range of the electromagnetic spectrum. Moreover, their optical properties are very sensitive to any conformational perturbations, as was successfully demonstrated in sensory devices. [25,26] Conformation-induced mechanochromism was already demonstrated A novel mechanism for well-pronounced mechanochromism in blends of a π-conjugated polymer based on reversible conformational transitions of a chromophore rather than caused by its aggregation state, is exemplified. Particularly, a strong stretching-induced bathochromic shift of the light absorption, or hypsochromic shift of the emission, is found in blends of the water-soluble poly(3-tri(ethylene glycol)) (P3TEOT) embedded into the matrix of thermoplastic polyvinyl alcohol. This counterintuitive phenomenon is explaine...