TY - JOUR

T1 - Donor-acceptor stacking arrangements in bulk and thin-film high-mobility conjugated polymers characterized using molecular modelling and MAS and surface-enhanced solid-state NMR spectroscopy

AU - Chaudhari, Sachin R.

AU - Griffin, John M.

AU - Broch, Katharina

AU - Lesage, Anne

AU - Lemaur, Vincent

AU - Dudenko, Dmytro

AU - Olivier, Yoann

AU - Sirringhaus, Henning

AU - Emsley, Lyndon

AU - Grey, Clare P.

PY - 2017/4/1

Y1 - 2017/4/1

N2 - Conjugated polymers show promising properties as cheap, sustainable and solution-processable semiconductors. A key challenge in the development of these materials is to determine the polymer chain structure, conformation and packing in both the bulk polymer and in thin films typically used in devices. However, many characterisation techniques are unable to provide atomic-level structural information owing to the presence of disorder. Here, we use molecular modelling, magic-angle spinning (MAS) and dynamic nuclear polarisation surface-enhanced NMR spectroscopy (DNP SENS) to characterise the polymer backbone group conformations and packing arrangement in the high-mobility donor-acceptor copolymer diketopyrrolo-pyrrole-dithienylthieno[3,2-b] thiophene (DPP-DTT). Using conventional H-1 and C-13 solid-state MAS NMR coupled with density functional theory calculations and molecular dynamics simulations, we find that the bulk polymer adopts a highly planar backbone conformation with a laterally-shifted donor-on-acceptor stacking arrangement. DNP SENS enables acquisition of C-13 NMR data for polymer films, where sensitivity is limiting owing to small sample volumes. The DNP signal enhancement enables a two-dimensional H-1-C-13 HETCOR spectrum to be recorded for a drop-cast polymer film, and a C-13 CPMAS NMR spectrum to be recorded for a spin-coated thin-film with a thickness of only 400 nm. The results show that the same planar backbone structure and intermolecular stacking arrangement is preserved in the films following solution processing and annealing, thereby rationalizing the favourable device properties of DPP-DTT, and providing a protocol for the study of other thin film materials.

AB - Conjugated polymers show promising properties as cheap, sustainable and solution-processable semiconductors. A key challenge in the development of these materials is to determine the polymer chain structure, conformation and packing in both the bulk polymer and in thin films typically used in devices. However, many characterisation techniques are unable to provide atomic-level structural information owing to the presence of disorder. Here, we use molecular modelling, magic-angle spinning (MAS) and dynamic nuclear polarisation surface-enhanced NMR spectroscopy (DNP SENS) to characterise the polymer backbone group conformations and packing arrangement in the high-mobility donor-acceptor copolymer diketopyrrolo-pyrrole-dithienylthieno[3,2-b] thiophene (DPP-DTT). Using conventional H-1 and C-13 solid-state MAS NMR coupled with density functional theory calculations and molecular dynamics simulations, we find that the bulk polymer adopts a highly planar backbone conformation with a laterally-shifted donor-on-acceptor stacking arrangement. DNP SENS enables acquisition of C-13 NMR data for polymer films, where sensitivity is limiting owing to small sample volumes. The DNP signal enhancement enables a two-dimensional H-1-C-13 HETCOR spectrum to be recorded for a drop-cast polymer film, and a C-13 CPMAS NMR spectrum to be recorded for a spin-coated thin-film with a thickness of only 400 nm. The results show that the same planar backbone structure and intermolecular stacking arrangement is preserved in the films following solution processing and annealing, thereby rationalizing the favourable device properties of DPP-DTT, and providing a protocol for the study of other thin film materials.

KW - DYNAMIC NUCLEAR-POLARIZATION

KW - FIELD-EFFECT TRANSISTORS

KW - MAGNETIC-RESONANCE-SPECTROSCOPY

KW - AMBIPOLAR CHARGE-TRANSPORT

KW - HIGH-PERFORMANCE AMBIPOLAR

KW - METAL-ORGANIC FRAMEWORKS

KW - ALKYL SIDE-CHAINS

KW - NATURAL-ABUNDANCE

KW - SUPRAMOLECULAR SYSTEMS

KW - DNP-NMR

U2 - 10.1039/c7sc00053g

DO - 10.1039/c7sc00053g

M3 - Journal article

VL - 8

SP - 3126

EP - 3136

JO - Chemical Science

JF - Chemical Science

SN - 2041-6520

IS - 4

ER -