The present work demonstrates one of the first examples of π-conjugated photonic switches (or photonic wave plates) based on the tailor-made π-conjugated polymer anisotropic organogel. New semicrystalline segmented π-conjugated polymers are designed with rigid aromatic oligophenylenevinylene π-core and flexible alkyl chain along the polymer backbone. These polymers are found to be self-assembled as semicrystalline or amorphous with respect to the number of carbon atoms in the alkyl units. These semicrystalline polymers produce organogels having nanofibrous morphology of 20 nm thickness with length up to 5 μm. The polymer organogel is aligned in a narrow glass capillary, and this anisotropic gel device is further demonstrated as photonic switches. The glass capillary device behaves as typical λ/4 photonic wave plates upon the illumination of the plane polarized light. The λ/4 photonic switching ability is found to be maximum at θ = 45° angle under the cross polarizers. The orthogonal arrangements of the gel capillaries produce dark and bright spots as on-and-off optical switches. Thermoreversibility of the polymer organogel (also its xerogel) was exploited to construct thermoresponsive photonic switches for the temperature window starting from 25 to 160 °C. The organic photonic switch concept can be adapted to large number of other π-conjugated materials for optical communication and storage.

We report aromatic π-stack-driven helical self-assemblies of segmented poly(phenylenevinylene)s and their hierarchical helical donor–acceptor assemblies with electron deficient molecules by a solvent-induced self-organization process. New segmented PPVs were designed and synthesized having tricyclodecane-substituted oligophenylenevinylene (OPV) π-core with flexible methylene chains of variable carbon atoms 4, 8, and 12. The polymers were obtained in high molecular weights with very good solubility in common organic solvents. The polymers were found to be amorphous, and their glass transition temperature varied from 100 to 170 °C with respect to the increase in the rigidity of the polymer backbone. The flexible segmented polymer underwent aromatic π-stack interaction to produce π-conjugated polymer aggregates in methanol and tetrahydrofuran (THF) solvent combinations. Electron microscopic studies confirmed that these π-aggregates appeared as bundles of helical assemblies. An electron deficient perylenebisimide derivative was complexed with segmented polymers to produce stable and helical donor–acceptor hierarchical assemblies. The formation of D–A assemblies was confirmed by detail photophysical studies such as absorbance, emission, time-resolved fluorescence decay, and FRET mechanism. A controlled experiment with structurally identical rigid polymer revealed that appropriate polymer design in the segmented skeleton is essential for making stable helical D–A assemblies. Thus, the present study provides insight into the formation of stable helical donor–acceptor assemblies in π-conjugated polymers that are useful for application in optoelectronics.

We report a unique color tunable amphiphilic segmented π-conjugated polymer design and their π-stack driven diverse self-assembled nanostructures and demonstrate their application as a new classes of aqueous luminescent nanoparticle probes for bioimaging in cervical and breast cancer cells. Oligo-phenylenevinylene (OPV) was employed as rigid luminescent π-core and oligo-ethyleneoxy chains were used as flexible spacers to construct new amphiphilic segmented π-conjugated polymers by Witting–Horner polymerization route. The rigidity of the π-core was varied using tricyclodecanemethyleneoxy, 2-ethylhexyloxy or methoxy pendants and appropriate π-core geometry was optimized to achieve maximum aromatic π-stacking interactions. Solvent-induced chain aggregation of the polymers exhibited a morphological transition from one-dimensional helical nanofibrous to three-dimensional spherical nanoassemblies in good/bad solvent combinations. This morphological transformation was accompanied by the fluorescence color change from blue-to-white-to-yellow. CIE color coordinates exhibited x = 0.25 and y = 0.32 for the white light followed by the collective emission from aggregated and isolated OPV chromophores. Electron and atomic microscopes, steady state photophysical studies, time-resolved fluorescent decay analysis, and dynamic light scattering method enabled us to establish the precise mechanism for the self-assembly of segmented OPV polymers. The polymers produced stable and luminescent aqueous nanoparticles of <200 nm diameter in water. Cytotoxicity studies in cervical and breast cancer cells revealed that these new aqueous luminescent polymer nanoparticles are highly biocompatible and nontoxic to cells up to 60 μg/mL. Cellular uptake studies by confocal microscope further exposed that these nanoparticles were internalized in the cancer cells and they were predominantly accumulated in the nucleus. The present investigation opens up new amphiphilic segmented π-conjugated polymer design for producing diverse supramolecular assemblies and also demonstrates their new application as biocompatible fluorescent nanoprobes for imaging in cancer cells.

Colors responsive to the chemical environment can form the basis for simple and highly accessible diagnostic tools. Herein, the charge modulation of conjugated polymers is demonstrated as a new mechanism for chemically responsive structural colors based on thin-film interference. A liquid−liquid interfacial self-assembly is employed to create a conjugated block copolymer film that is flexible, transferable, and highly homogeneous in thickness over a large area. Gold (Au) complexes are introduced in the self-assembly process for in situ oxidation of conjugated polymers into a hole-polaronic state that renders the polymer film responsive to the chemical environment. When transferred onto a reflective substrate, the film shows thickness-dependent tunable reflective colors due to the optical interference. Furthermore, it experiences drastic changes in its dielectric behavior upon switching of the polaronic state, thereby enabling large modulations to the interferometric colors. Such responsive thin-film colors, in turn, can be used as a simple and intuitive multicolor readout for the recognition of reductive vapors including biological decomposition products.

Direct evidence for non-covalent secondary interactions in planar and nonplanar aromatic π-conjugates and their solid-state assemblies is established. A series of horizontally, vertically, and radially expanded oligo(phenylenevinylene)s (H-OPVs, V-OPVs, and R-OPVs, respectively) were designed with a fixed π-core and variable alkyl chain lengths on the periphery. Single-crystal structures of the OPVs were resolved to trace the secondary interactions that direct the solid-state self-organization and molecular packing of the chromophores. The H-OPVs were found to be planar, and they did not show any secondary interactions in the crystal lattices. The V-OPVs and R-OPVs were found to be nonplanar and to exhibit multiple CH/π hydrogen-bonding interactions among aryl hydrogen donors and acceptors. The enthalpies of the melting and crystallization transitions revealed that the planar H-OPVs are highly crystalline compared with the nonplanar R-OPVs and V-OPVs. Polarized light microscopy studies revealed the formation of one-dimensional nematic mesophases in H-OPVs. The absolute solid-state photoluminescence quantum yields (PLQYs) of the OPVs were determined using an integrating sphere setup. The highly packed H-OPVs showed low PLQYs compared with those of the weakly packed V-OPVs and R-OPVs. Time-resolved fluorescence decay measurements revealed that the excited-state decay dynamics of highly packed H-OPVs was much faster with respect to their low PLQYs. The decay profiles were found to be relatively slow (with higher life time (τ)) in the V-OPVs and R-OPVs. A field-effect transistor (FET) device was constructed for an OPV sample that showed a hole carrier mobility in the range of 10(-5) cm(2) V(-1) s(-1). The present investigation thus provides a new opportunity to trace the role of secondary interactions on π-conjugated mesophase self-assemblies and their solid-state emission and FET devices, more specifically based on OPV chromophores.

Here, we report the magnetic field-induced selfassembly of a conjugated block copolymer, poly(3-hexylthiopene)block-poly(ethylene glycol) (P3HT-b-PEG), and iron oxide nanoparticles (IONPs) at the air−water interface. Binary selfassembly of P3HT-b-PEG and IONPs at the interface results in nanoparticle-embedded P3HT-b-PEG nanowire arrays with a micrometer-scale domain size. Under the magnetic field, the field-induced magnetic interaction significantly improves the degree of order, generating long-range ordered, direction-controlled nanoarrays of P3HT-b-PEG and IONPs, where IONPs are aligned in the direction of the magnetic field over a sub-millimeter scale. The size of IONPs is an important factor for the formation of an ordered assembly structure at the nanometer scale, as it dictates the magnetic dipole interaction and the entropic interaction between nanoparticles and polymers. The consideration of magnetic dipole interactions suggests that the field-induced self-assembly occurs through the formation of intermediate magnetic subunits composed of short IONP strings along the semirigid P3HT nanowires, which can be aligned through the magnetic interactions, ultimately driving the long-range ordered self-assembly. This study demonstrates for the first time that the magnetic field-induced self-assembly can be used to generate macroscopically ordered polymer films with a nanometer-scale order in low fields.

We report one of the first examples of room temperature stable solid-state charge transfer (CT) complexes based on a segmented π-conjugated polymer and rylene diimide donor–acceptor system having tunable optical transitions from the visible to NIR region in the solar spectrum. Semicrystalline and amorphous segmented oligo-phenylenevinylene (OPV) chromophore containing polymers were tailor-made with flexible polymethylene chains in the backbone. The electron rich segmented OPV polymers were complexed with two electron-deficient diimides based on naphthalene (NDI) and phenylene (PDI) core. The binary complexes of segmented OPV polymers and rylene diimides produced unique classes of CT complexes based on OPV-NDI and OPV-PDI chromophore diads. Electron microscope, polarizing microscope, and X-ray diffraction analyses provided direct evidence for the two-dimensional lamellar packing of D–A self-assembly in the solid state. Detailed absorption and emission photophysical studies revealed that the donor OPV polymers and acceptor chromophores exhibited a 1:1 complex with respect to the long-range order of D–A–D–A–D–A π-stacked supramolecular assemblies. The role of the macromolecular effect on the CT complexation was further investigated using structurally identical OPV monomers. The monomer OPV-NDI complexes (or PDI complexes) were found to exhibit CT complex in the solution; however, they underwent uncontrollable phase separation into their individual D and A crystalline domains and lost their CT self-assembly in the solid state. Interestingly, the macromolecular effect driven supramolecular self-organization of long chain segmented OPV polymers produced stable CT complexes both in solution and solid state under ambient conditions. Segmented OPV polymer + PDI and segmented OPV polymer + NDI complexes were produced as red and green colored CT complexes, respectively. This enabled the accomplishment of room temperature stable CT complexes in π-conjugated polymers having absorption ranging from 350 to 1100 nm. These donor–acceptor CT self-assemblies are processable into thin films under solvent free melt crystallization process; thus, the present segmented polymer design strategy opens up a platform for donor–acceptor CT complexes.

Here, we report charge-transfer-driven self-assembly of conjugated block copolymers (BCP) into highly doped conjugated polymer nanofibers. The ground-state integer charge transfer (ICT) between a BCP composed of poly(3-hexylthiophene) and poly(ethylene oxide) (P3HT-b-PEO) and electrondeficient 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) induced spontaneous self-assembly of the donor and the acceptor into well-defined one-dimensional nanofibers. The presence of the PEO block plays an important role for the selfassembly by providing a polar environment that can stabilize nanoscale charge transfer (CT) assemblies. The doped nanofibers were responsive to various external stimuli such as heat, chemical, and light and exhibited efficient photothermal properties in the near-IR region. The CT-driven BCP self-assembly reported here provides a new platform for the fabrication of highly doped semiconductor nanostructures.