Helical Self-Assemblies of Segmented Poly(phenylenevinylene)s and Their Hierarchical Donor–Acceptor Complexes

Abstract

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.

Self-Assembly of n-Shaped Rod–Coil Molecules into Thermoresponsive Nanoassemblies: Construction of Reversible Helical Nanofibers in Aqueous Environment

“…Corresponding to the extended molecular lengths of the rod and coil segments, these molecular arrangements adopt a rotational packing and subsequently self-assemble into nanofibers where molecules are arranged perpendicularly to the fiber axis. The observed supramolecular handedness may arise from steric constraints imposed by the chiral centers in the rod–coil molecular systems. − To decrease the steric hindrance between the coil segment and the methyl groups at the surface of the rod and coil segments, the n-shaped rod building blocks of molecules 2 and 3 stack on top of each other and tilt in the same direction to minimize the energy balance between the π–π stacking interaction of the rod segments and the repulsive effect of the nearby PEO coil chains. − Thus, this type of molecular arrangement leads to the creation of helical nanofibers, with a core consisting of a hydrophobic n-shaped rod building block, surrounded by hydrophilic PEO coil chains with lateral alkyl chains exposed to the aqueous environment (Figure b,d).…”

Fluorescent-Tagged Biodegradable Polycaprolactone Block Copolymer FRET Probe for Intracellular Bioimaging in Cancer Cells

“…On the other hand, the polymers showed 50 nm red-shift in water (maxima at 495 nm) followed by strong aggregation. Aromatic π-conjugated chromophores such as OPV are well known to undergo π–π stacking depending upon the solvent environment. , Thus, the large red shift in the emission maxima was attributed to the emission from the J-type aggregates by the hairpin-like micellar self-assembly of OPV chromophores. Further, the emission spectra in thin film showed maxima at 495 nm which was almost identical to that of their emission spectra in water.…”

Color-Tunable Amphiphilic Segmented π-Conjugated Polymer Nano-Assemblies and Their Bioimaging in Cancer Cells

“…The molecular weights of the polymers were obtained as M w = 16 800 to 28 000 g/mol with a polydispersity of 2.0 to 3.5 (see Table ST1). The Witting−Horner polymerization route is typically known to produce polymers with 10−15 repeating units as observed by us 51,47 and others. 36 For biomedical applications, polymer molecular weights of <40 000 g/mol are preferred due to their easy clearance through the kidney.…”

“…46 Further, oligo-1,4-phenylenevinylenes (OPV) segmented polymers were studied for helical donor−acceptor assemblies. 47 Semicrystalline OPV segmented polymers were designed and self-assembled as organogels to demonstrate their photonic λ/4 wave plates for optical switching applications. 48 These studies emphasized the importance of segmented π-conjugated polymers for photonic and electronic applications.…”