Disorder in P3HT Nanoparticles Probed by Optical Spectroscopy on P3HT-b-PEG Micelles

Abstract

We employ photoluminescence (PL) spectroscopy on individual nanoscale aggregates of the conjugated polymer poly(3-hexylthiophene), P3HT, at room temperature (RT) and at low temperature (LT) (1.5 K), to unravel different levels of structural and electronic disorder within P3HT nanoparticles. The aggregates are prepared by self-assembly of the block copolymer P3HT- block -poly(ethylene glycol) (P3HT- b -PEG) into micelles, with the P3HT aggregates constituting the micelles’ core. Irrespective of temperature, we find from the intensity ratio between the 0–1 and 0–0 peaks in the PL spectra that the P3HT aggregates are of H-type nature, as expected from π-stacked conjugated thiophene backbones. Moreover, the distributions of the PL peak ratios demonstrate a large variation of disorder between micelles (inter-aggregate disorder) and within individual aggregates (intra-aggregate disorder). Upon cooling from RT to LT, the PL spectra red-shift by 550 cm –1 , and the energy of the (effective) carbon-bond stretch mode is reduced by 100 cm –1 . These spectral changes indicate that the P3HT backbone in the P3HT- b -PEG copolymer does not fully planarize before aggregation at RT and that upon cooling, partial planarization occurs. This intra-chain torsional disorder is ultimately responsible for the intra- and inter-aggregate disorder. These findings are supported by temperature-dependent absorption spectra on thin P3HT films. The interplay between intra-chain, intra-aggregate, and inter-aggregate disorder is key for the bulk photophysical properties of nanoparticles based on conjugated polymers, for example, in hierarchical (super-) structures. Ultimately, these properties determine the usefulness of such structures in hybrid organic–inorganic materials, for example, in (bio-)sensing and optoelectronics applications.

Directed Gradients in the Excited-State Energy Landscape of Poly(3-hexylthiophene) Nanofibers

“…When going from the beginning of the P3HT nanofibers (spot A) toward their middle (spot B) and into the P3HT film (spot C), we find from the fits to the spectra in Figure b that the free exciton bandwidth increases from 193 to 248 meV (Table ). While this range of values is in agreement with literature data, ,, the substantial change of this parameter within the same sample (in fact, within a few micrometers of our sample) is remarkable. Along the same direction (from A to C), the spectral position of the lowest-energy absorption peak A 1 of the crystalline phase E A1 Abs blue-shifts by 10 meV, starting from 2.043 eV at spot A (Table ).…”

“…Here, we exploit defect fractionation during the growth of nanofibers based on a conjugated polymer to realize a gradient in the excited-state energy landscape over micrometer distances. We employ a highly efficient ribbon-like supramolecular nucleating agent (NA) for the controlled crystallization of the extensively studied and well-understood poly­(3-hexylthiophene), P3HT, − into nanofibers. The resulting NA/P3HT superstructures, resembling shish-kebab-like structures, , with their highly aligned and oriented micrometer-long P3HT nanofibers allow us to use hyperspectral imaging, i.e., spatially resolved absorption and emission spectroscopy.…”

Effect of Ultraviolet Activation on Sub-ppm NO2 Sensing Dynamics of Poly(3-hexylthiophene)-Bearing Graft Copolymers

“…DodecSIL (Figure 2b,d) exhibits a more uniform non-porous structure with an average of 10 nm (± 2.5 nm) height variation. The root mean square height (RMS) values for 5 × 5 µm areas of the structures were equal to 3.7 ± 0.1 nm and 2.3 ± 0.1 nm for SilPEG and DodeSIL, respectively [34,35]. This shows that the morphology of SilPEG is more developed than that of DodecSILs.…”

Copolymers of Gelatin-graft-poly(3-hexylthiophene) for Transient Electronics

“…Here, Gel- g -P3HT-2 was drop-cast or spin-coated on mica and a Si (100) wafer substrate for the AFM and GIWAXS experiments, respectively. AFM height and phase images (Figure S10) showed clear aggregates of P3HT in a thin film of Gel- g -P3HT-2 spin-coated from the aqueous solution . In contrast, as depicted in the height profiles shown in Figure S10, the Gel- g -P3HT-2 spin-coated from THF/H 2 O system exhibited different surface morphologies, characterized by small concavities within a “donat”-like structures.…”