Oligo-p-phenylenevinylene (OPV) materials monofunctionalised with ureido-s-triazine form chiral, helical stacks in dodecane solution. Here, we investigate resonance energy transfer dynamics in ...supramolecular stacks of OPVs consisting of three phenyl rings (MOPV3) doped with similar oligomers containing four phenyl rings (MOPV4). Broad spectral overlap between the MOPV3 fluorophores and MOPV4 chromophores results in efficient energy transfer from MOPV3 to MOPV4. We observe resonance energy transfer following two distinct regimes. The first is evident by growth of MOPV4 photoluminescence on a timescale of ∼50ps, mediated by rapid exciton diffusion in MOPV3 within the stack. In the second regime, dynamics of localised excitons on nanosecond timescales are dominated by direct resonance energy transfer to MOPV4 chromophores. Global analysis of the photoluminescence decay of MOPV3 in blends with varying MOPV4 composition on times ≳2ns is consistent with quasi-one-dimensional resonance energy transfer with Förster radius of 8nm.
Combining conjugated poylmers and TiO
2
in hybrid bulk‐heterojunctions is a promising method for producing novel solar cells. Here TiO
2
is introduced into a poly(
p
‐phenylene vinylene) layer. ...Nanometer‐scale phase separation allows efficient photoinduced charge transfer between the two components. The films can be used as the active layer in a photovoltaic cell and provide external quantum efficiencies of up to 11 % (see Figure).
Phys. Rev. Lett. 98, 146101 (2007) High magnetic fields were used to deform spherical nanocapsules,
self-assembled from bola-amphiphilic sexithiophene molecules. At low fields the
deformation -- ...measured through linear birefringence -- scales quadratically
with the capsule radius and with the magnetic field strength. These data
confirm a long standing theoretical prediction (W. Helfrich, Phys. Lett. {\bf
43A}, 409 (1973)), and permits the determination of the bending rigidity of the
capsules as (2.6$\pm$0.8)$\times 10^{-21}$ J. At high fields, an enhanced
rigidity is found which cannot be explained within the Helfrich model. We
propose a complete form of the free energy functional that accounts for this
behaviour, and allows discussion of the formation and stability of nanocapsules
in solution.
High magnetic fields were used to deform spherical nanocapsules, self-assembled from bola-amphiphilic sexithiophene molecules. At low fields the deformation -- measured through linear birefringence ...-- scales quadratically with the capsule radius and with the magnetic field strength. These data confirm a long standing theoretical prediction (W. Helfrich, Phys. Lett. {\bf 43A}, 409 (1973)), and permits the determination of the bending rigidity of the capsules as (2.6\(\pm\)0.8)\(\times 10^{-21}\) J. At high fields, an enhanced rigidity is found which cannot be explained within the Helfrich model. We propose a complete form of the free energy functional that accounts for this behaviour, and allows discussion of the formation and stability of nanocapsules in solution.
Extracellular microenvironment is highly dynamic where spatiotemporal regulation of cell‐instructive cues such as matrix topography tightly regulates cellular behavior. Recapitulating dynamic changes ...in stimuli‐responsive materials has become an important strategy in regenerative medicine to generate biomaterials which closely mimic the natural microenvironment. Here, light responsive liquid crystal polymer networks are used for their adaptive and programmable nature to form hybrid surfaces presenting micrometer scale topographical cues and changes in nanoscale roughness at the same time to direct cell migration. This study shows that the cell speed and migration patterns are strongly dependent on the height of the (light‐responsive) micrometer scale topographies and differences in surface nanoroughness. Furthermore, switching cell migration patterns upon in situ temporal changes in surface nanoroughness, points out the ability to dynamically control cell behavior on these surfaces. Finally, the possibility is shown to form photoswitchable topographies, appealing for future studies where topographies can be rendered reversible on demand.
Light‐responsive (dynamic) interfaces on liquid crystal polymer networks present a new way to encode the surface topography of a biomaterial. Photoisomerization of azobenzene molecule conjugated in the network leads to changes in the order of the liquid crystal molecules resulting in volume changes in the illuminated areas, generating predesigned responsive topographical features in order to instruct cell behavior.
Hierarchical self-assembly offers a powerful strategy for producing molecular nanostructures. Although widely used, the mechanistic details of self-assembly processes are poorly understood. We ...spectroscopically monitored a nucleation process in the self-assembly of p-conjugated molecules into helical supramolecular fibrillar structures. The data support a nucleation-growth pathway that gives rise to a remarkably high degree of cooperativity. Furthermore, we characterize a helical transition in the nucleating species before growth. The self-assembly process depends strongly on solvent structure, suggesting that an organized shell of solvent molecules plays an explicit role in rigidifying the aggregates and guiding them toward further assembly into bundles and/or gels.
Light responsive materials that are able to change their shape are becoming increasingly important. However, preconfigurable bistable or even multi‐stable visible light responsive coatings have not ...been reported yet. Such materials will require less energy to actuate and will have a longer lifetime. Here, it is shown that fluorinated azobenzenes can be used to create rewritable and pre‐configurable responsive surfaces that show multi‐stable topographies. These surface structures can be formed and removed by using low intensity green and blue light, respectively. Multistable preconfigured surface topographies can also be created in the absence of a mask. The method allows for full control over the surface structures as the topographical changes are directly linked to the molecular isomerization processes. Preliminary studies reveal that these light responsive materials are suitable as adaptive biological surfaces.
Multistable, re‐ and preconfigurable visible light responsive liquid crystal coatings are fabricated by using low illumination doses. Surface topographies can be configured by masked exposure or with patterned coatings. Preliminary results show that such coatings could act as bio‐scaffolds.
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