One of the most inspiring and puzzling developments in the organic electronics community in the last few years has been the emergence of solution-processable semiconducting polymers that lack significant long-range order but outperform the best, high-mobility, ordered semiconducting polymers to date. Here we provide new insights into the charge-transport mechanism in semiconducting polymers and offer new molecular design guidelines by examining a state-of-the-art indacenodithiophene-benzothiadiazole copolymer having field-effect mobility of up to 3.6 cm 2 V À 1 s À 1 with a combination of diffraction and polarizing spectroscopic techniques. Our results reveal that its conjugated planes exhibit a common, comprehensive orientation in both the non-crystalline regions and the ordered crystallites, which is likely to originate from its superior backbone rigidity. We argue that charge transport in high-mobility semiconducting polymers is quasi one-dimensional, that is, predominantly occurring along the backbone, and requires only occasional intermolecular hopping through short p-stacking bridges.
We describe a series of highly soluble diketo pyrrolo-pyrrole (DPP)-bithiophene copolymers exhibiting field effect hole mobilities up to 0.74 cm(2) V(-1) s(-1), with a common synthetic motif of bulky 2-octyldodecyl side groups on the conjugated backbone. Spectroscopy, diffraction, and microscopy measurements reveal a transition in molecular packing behavior from a preferentially edge-on orientation of the conjugated plane to a preferentially face-on orientation as the attachment density of the side chains increases. Thermal annealing generally reduces both the face-on population and the misoriented edge-on domains. The highest hole mobilities of this series were obtained from edge-on molecular packing and in-plane liquid-crystalline texture, but films with a bimodal orientation distribution and no discernible in-plane texture exhibited surprisingly comparable mobilities. The high hole mobility may therefore arise from the molecular packing feature common to the entire polymer series: backbones that are strictly oriented parallel to the substrate plane and coplanar with other backbones in the same layer.
During nuclear waste
disposal process, radioactive iodine as a
fission product can be released. The widespread implementation of
sustainable nuclear energy thus requires the development of efficient
iodine stores that have simultaneously high capacity, stability and
more importantly, storage density (and hence minimized system volume).
Here, we report high I2 adsorption in a series of robust
porous metal–organic materials, MFM-300(M) (M = Al, Sc, Fe,
In). MFM-300(Sc) exhibits fully reversible I2 uptake of
1.54 g g–1, and its structure remains completely
unperturbed upon inclusion/removal of I2. Direct observation
and quantification of the adsorption, binding domains and dynamics
of guest I2 molecules within these hosts have been achieved
using XPS, TGA-MS, high resolution synchrotron X-ray diffraction,
pair distribution function analysis, Raman, terahertz and neutron
spectroscopy, coupled with density functional theory modeling. These
complementary techniques reveal a comprehensive understanding of the
host–I2 and I2–I2 binding
interactions at a molecular level. The initial binding site of I2 in MFM-300(Sc), I2I, is located near
the bridging hydroxyl group of the [ScO4(OH)2] moiety [I2I···H–O =
2.263(9) Å] with an occupancy of 0.268. I2II is located interstitially between two phenyl rings of neighboring
ligand molecules [I2II···phenyl
ring = 3.378(9) and 4.228(5) Å]. I2II is
4.565(2) Å from the hydroxyl group with an occupancy of 0.208.
Significantly, at high I2 loading an unprecedented self-aggregation
of I2 molecules into triple-helical chains within the confined
nanovoids has been observed at crystallographic resolution, leading
to a highly efficient packing of I2 molecules with an exceptional
I2 storage density of 3.08 g cm–3 in
MFM-300(Sc).
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