Pressure Modulation of Backbone Conformation and Intermolecular Distance of Conjugated Polymers Toward Understanding the Dynamism of π-Figuration of their Conjugated System

Abstract

Continuous tuning of the backbone conformation and interchain distance of a π-conjugated polymer is an essential prerequisite to unveil the inherent electrical and optical features of organic electronics. To this end, applying pressure in a hydrostatic medium or diamond anvil cell is a facile approach without the need for side-chain synthetic engineering. We report the development of high-pressure, time-resolved microwave conductivity (HP-TRMC) and evaluation of transient photoconductivity in the regioregular poly(3-hexylthiophene) (P3HT) film and its bulk heterojunction blend with methanofullerene (PCBM). X-ray diffraction experiments under high pressure were performed to detail the pressure dependence of π-stacking and interlamellar distances in P3HT crystallites and PCBM aggregates. The HP-TRMC results were further correlated with high-pressure Raman spectroscopy and density functional theory calculation. The increased HP-TRMC conductivity of P3HT under pressure was found to be relevant to the planarity of the backbone conformation and intramolecular hole mobility. The effects of pressure on the backbone planarity are estimated to be ∼0.3 kJ mol(-1) based on the compressibility derived from the X-ray diffraction under high pressure, suggesting the high enough energy to cause modulation of the planarity in terms of the Landau-de Gennes free energy of isolated P3HT chains as 0.23 kJ mol(-1). In contrast, the P3HT:PCBM blend showed a simple decrease in photoconductivity irrespective of the identical compressive behavior of P3HT. A mechanistic insight into the interplay of intra- and intermolecular mobilities is a key to tailoring the dynamic π-figuration associated with electrical properties, which may lead to the use of HP-TRMC for exploring divergent π-conjugated materials at the desired molecular arrangement and conformation.

Unraveling Inter‐ and Intrachain Electronics in Polythiophene Assemblies Mediated by Coordination Nanospaces

“…Fore xample, although the emission peak of bulk PThw as not changed before and after the addition of MeOH (Supporting Information, Figure S12), al arge blue-shift is observed when the PThcomposites were subjected to MeOH vapor (Figure 3a). [19] As the adsorption isotherm of MeOH for 1'PTh·5 shows as teep rise even in the low-pressure region, it demonstrates that the hybridization of functional polymers within porous materials is ak ey strategy for sensing systems intended to detect very low concentration of vapors (Supporting Information, Figure S15). Although the blue-shifting of the emission of polythiophene upon exposure to methanol is contradictory to what is observed for bulk PTh, it can be rationalized by the coordination of MeOH molecules to the open metal sites of 1,aphenomenon that is confirmed by single crystal analysis in analogous systems.…”

“…Raman spectra of 1'PTh·5 upon exposure to MeOH vapor shows as hift in the band at 1454 cm À1 to longer wavenumber,a nd can be attributed to al oss of planarity of the backbone (Supporting Information , Figure S14). [19] As the adsorption isotherm of MeOH for 1'PTh·5 shows as teep rise even in the low-pressure region, it demonstrates that the hybridization of functional polymers within porous materials is ak ey strategy for sensing systems intended to detect very low concentration of vapors (Supporting Information, Figure S15).…”

Measuring structural inhomogeneity of a helical conjugated polymer at high pressure and temperature

“…High pressure structural studies of π‐conjugated polymers are motivated by the fact that hydrostatic pressure enhances intermolecular interactions and changes intramolecular geometry without chemical changes. These experiments were pioneered by Mårdalen et al, who reported on the structural and optical transitions for polythiophenes, paving the way for polythiophene studies with fullerene derivatives . These studies were augmented by structural high pressure studies of polyphenylenes by Heimel et al and Gitsas et al, and by optical high pressure studies including studies of poly( p‐ phenylene vinylene) by Morandi et al and investigations of fluorene copolymers by Schmidtke et al Common to all these studies are planarization of otherwise twisted polymers followed by a redshift in photoluminescence (PL).…”

Unraveling the Solution‐State Supramolecular Structures of Donor–Acceptor Polymers and their Influence on Solid‐State Morphology and Charge‐Transport Properties

“…This indicates that in ODCB, polymer chains form 1D aggregates by several interchain π–π stacking (Figure e), in agreement with temperature‐dependent absorption spectra. The Kuhn length equals to the total length of sixteen repeating units of BDOPV‐2T, significantly larger than those of P3HT, indicating the rigidness of polymer backbone in ODCB solution, due to the intramolecular hydrogen bonding. The radius obtained from SANS fitting is comparable to the molecular modeling results of 28.5 Å.…”