Three different pi-conjugated oligomers (a blue-emitting oligofluorene, a green-emitting oligo(phenylene vinylene), and a red-emitting perylene bisimide) have been functionalized with self-complementary quadruple hydrogen bonding ureidopyrimidinone (UPy) units at both ends. The molecules self-assemble in solution and in the bulk, forming supramolecular polymers. When mixed together in solution, random noncovalent copolymers are formed that contain all three types of chromophores, resulting in energy transfer upon excitation of the oligofluorene energy donor. At a certain mixing ratio, a white emissive supramolecular polymer can be created in solution. In contrast to their unfunctionalized counterparts, bis-UPy-chromophores can easily be deposited as smooth thin films on surfaces by spin coating. No phase separation is observed in these films, and energy transfer is much more efficient than in solution, giving rise to white fluorescence at much lower ratios of energy acceptor to donor. Light emitting diodes based on these supramolecular polymers have been prepared from all three types of pure materials, yielding blue, green, and red devices, respectively. At appropriate mixing ratios of these three compounds, white electroluminescence is observed. This approach yields a toolbox of molecules that can be easily used to construct pi-conjugated supramolecular polymers with a variety of compositions, high solution viscosities, and tuneable emission colors.

A set of fluorene oligomers has been synthesized by stepwise palladium-catalyzed (Suzuki) couplings of fluorene monomers. Ureidopyrimidinones (UPy), functional groups that can dimerize via quadruple hydrogen bonds, were attached to both ends of the oligofluorenes. The resulting bis-UPy-terminated oligomers self-assemble into supramolecular chain polymers. For comparison, oligofluorenes of the same oligomer lengths but without terminal hydrogen-bonding groups were synthesized. Chains of hydrogen-bonded fluorenes can be simply endcapped by a variety of chain stoppers, molecules that have one UPy group. In this manner, we have endcapped the hydrogen-bonded fluorene chains with either oligo(p-phenylenevinylene) or perylene bisimide. Energy-transfer experiments in solution and the solid state demonstrate that oligofluorenes can donate energy to a variety of energy acceptors, but that this energy transfer occurs most effectively when the donor fluorene is hydrogen-bonded to the acceptor.

Structural and kinetic exchange properties of supramolecular polymers composed of mono- and bivalent ureidopyrimidinone-based monomers are investigated in aqueous solutions. It is shown that exchange dynamics can be controlled by mixing different types of monomers. This tunability widens the scope in their design as biomaterials.

Addressing the properties and interactions of individual selfassembled architectures is of great importance for the actual implementation of such objects in bio-and nanotechnological applications.[1] Supramolecular electronics depends on the ability to control the ordering of p-conjugated systems into well-defined, functional structures.[2] In natural photosynthetic systems, such a controlled organization yields directional energy and electron transfer in an aqueous environment.[3] Remarkably, only a few reports exist on selfassembled p-conjugated systems in water.[4] Our previous work on energy [5] and electron [6] transfer in self-assembled oligo(p-phenylene vinylene) (OPV) assemblies, [7] for example, focused on stacked oligomers in apolar solvents. [8] However, the interactions between self-assembled objects in water has become more appealing and challenging through the opportunities provided by scanning confocal microscopy. Herein we report on the use of fluorescence microscopy to characterize the properties and interactions of OPV assemblies in water by monitoring energy transfer.OPV5 (Scheme 1) was previously synthesized and shown to form chiral assemblies in water, but no further details with regard to the type of architecture was presented.[4b] By using scanning confocal microscopy we now give direct evidence for the formation of OPV vesicles, an arrangement rarely observed with p-conjugated oligomers.[9] In addition we synthesized the analogous cyano-substituted CN-OPV5[10] to study energy transfer in mixed donor/acceptor vesicles in bulk solution as well as in single vesicles, immobilized on a glass surface. Furthermore, the exchange of chromophores between vesicles over time could be monitored. CN-OPV5 was synthesized according to standard literature procedures, and was obtained as a red waxy solid which was fully characterized.[11] OPV5 was synthesized and characterized as reported previously.[4b] The optical properties of these two compounds were studied in various solvents by using UV/Vis, fluorescence, and circular dichroism (CD) spectroscopy (Figure 1). In general, CN-OPV5 displays similar properties to OPV5: CN-OPV5 is molecularly dissolved in chloroform, as indicated by a highly symmetrical pp* transition at l max = 482 nm, intense fluorescence at l em = 568 nm, and the absence of any Cotton effect. The effect of cyano substitution in CN-OPV5 on the HOMO-LUMO separation of the oligomer is clearly observed by comparison of the spectra with those of OPV5. The p-p* transition of CN-OPV5 is shifted 32 nm bathochromically in chloroform, a feature which is desired for making it an energy acceptor for OPV5.The absorption maximum of CN-OPV5 in water [12] displays a modest hypsochromic shift of 9 nm (to l max = 473 nm) relative to that in chloroform, and develops a shoulder extending to l = 600 nm. Its fluorescence is strongly quenched and red-shifted to l em = 638 nm, and concomitantly, a bisignate Cotton effect is observed, which is positive [+] at high energy and negative [À] at low energy (g max[+] ...

Producing lightweight polymeric actuators able to generate high stresses typical of hard metals and/or ceramics remains challenging. The photo-mechanical responses of ultra-drawn ultrahigh molecular weight polyethylene (UHMWPE) actuators containing azobenzene photo-switches with symmetrically attached polyethylene (PE) side chains are reported. Long PE side chains promote dispersion within the apolar UHMWPE matrix, and the ultra-drawn films are highly aligned. The ultra-drawn azobenzenedoped UHMWPE films have high Young's moduli ($100 GPa) and are viscoelastic at room temperature at strains below 1%. The photo-mechanical response of the films is fast (<1 s), showing a high specific actuation stress response (>6 3 10 4 Pa (kg m À3 ) À1 ) to UV or visible light at a low strain ($0.06%). The actuator responds to rotating linearly polarized light, causing a photoinduced stress wave response. Such rapid, high-stress, low-strain, photo-mechanical responses are unique in soft polymer systems with physical values approaching hard metals/ceramics.

We describe the synthesis, supramolecular ordering on surfaces and in solution, and photophysical characterization of OPV4UT-PERY, an oligo(p-phenylenevinylene) (OPV) with a covalently attached perylene bisimide moiety. In chloroform, the molecule forms dimers through quadruple hydrogen bonding of the ureido-s-triazine array. This is supported by scanning tunneling microscopy (STM) studies, which reveal dimer formation at the liquid (1,2,4-trichlorobenzene)/solid (graphite) interface. Moreover, contrast reversal in bias-dependent STM imaging provides information on the ordering and different electronic properties of the oligo(p-phenylenevinylene) and perylene bisimide moieties. In dodecane, the molecule self-assembles into H-type aggregates that are still soluble as a result of the hydrophobic shell formed by the dodecyloxy wedges. The donor-acceptor molecule is characterized by efficient energy transfer from the photoexcited OPV to the perylene bisimide. Mixed assemblies with analogous OPVs lacking the perylene bisimide unit have been prepared in dodecane solution and energy transfer to the incorporated perylene bisimides has been studied by fluorescence spectroscopy.

Addressing the properties and interactions of individual selfassembled architectures is of great importance for the actual implementation of such objects in bio-and nanotechnological applications.[1] Supramolecular electronics depends on the ability to control the ordering of p-conjugated systems into well-defined, functional structures.[2] In natural photosynthetic systems, such a controlled organization yields directional energy and electron transfer in an aqueous environment.[3] Remarkably, only a few reports exist on selfassembled p-conjugated systems in water.[4] Our previous work on energy [5] and electron [6] transfer in self-assembled oligo(p-phenylene vinylene) (OPV) assemblies, [7] for example, focused on stacked oligomers in apolar solvents. [8] However, the interactions between self-assembled objects in water has become more appealing and challenging through the opportunities provided by scanning confocal microscopy. Herein we report on the use of fluorescence microscopy to characterize the properties and interactions of OPV assemblies in water by monitoring energy transfer.OPV5 (Scheme 1) was previously synthesized and shown to form chiral assemblies in water, but no further details with regard to the type of architecture was presented.[4b] By using scanning confocal microscopy we now give direct evidence for the formation of OPV vesicles, an arrangement rarely observed with p-conjugated oligomers.[9] In addition we synthesized the analogous cyano-substituted CN-OPV5[10] to study energy transfer in mixed donor/acceptor vesicles in bulk solution as well as in single vesicles, immobilized on a glass surface. Furthermore, the exchange of chromophores between vesicles over time could be monitored. CN-OPV5 was synthesized according to standard literature procedures, and was obtained as a red waxy solid which was fully characterized.[11] OPV5 was synthesized and characterized as reported previously.[4b] The optical properties of these two compounds were studied in various solvents by using UV/Vis, fluorescence, and circular dichroism (CD) spectroscopy (Figure 1). In general, CN-OPV5 displays similar properties to OPV5: CN-OPV5 is molecularly dissolved in chloroform, as indicated by a highly symmetrical pp* transition at l max = 482 nm, intense fluorescence at l em = 568 nm, and the absence of any Cotton effect. The effect of cyano substitution in CN-OPV5 on the HOMO-LUMO separation of the oligomer is clearly observed by comparison of the spectra with those of OPV5. The p-p* transition of CN-OPV5 is shifted 32 nm bathochromically in chloroform, a feature which is desired for making it an energy acceptor for OPV5.The absorption maximum of CN-OPV5 in water [12] displays a modest hypsochromic shift of 9 nm (to l max = 473 nm) relative to that in chloroform, and develops a shoulder extending to l = 600 nm. Its fluorescence is strongly quenched and red-shifted to l em = 638 nm, and concomitantly, a bisignate Cotton effect is observed, which is positive [+] at high energy and negative [À] at low energy (g max[+] ...

The ability of foldamers to adopt a secondary structure in solution has been exploited to organize peripheral functionality. Our previously reported poly(ureidophthalimide) foldamer proved to be an excellent scaffold for the chiral organization of peripherally positioned oligo(p-phenylenevinylene) (OPV) chromophores. Facile high-yielding synthesis gave access to the required OPV-decorated building blocks. A condensation polymerization provided polymers of sufficient length to allow construction of a helical architecture comprising several turns. Short and long chains were separated by chromatography. Circular dichroism studies in THF of the longer chains indicate the presence of helically arranged OPVs. However, such an effect is not observed in CHCl3. Remarkable are the measurements of the OPV foldamers in heptane. A bisignate Cotton effect is observed in heptane of a sample with a THF history. No Cotton effect is observed in heptane of a sample with a CHCl3 history. In this example of supramolecular synthesis, the solvent dictates the expression of supramolecular chirality in a secondary structure. The short-chain oligomeric fractions that are unable to create a full turn revealed on scanning tunneling microscopy analysis the presence of circular architectures at the graphite/1-phenyloctane interface. This is in full agreement with the proposed conformation of the decorated foldamers.