little, if anything, to the observed improvement in charge-carrier mobility. NMR
rather unravels the complexity of this remarkable CDT-BTZ copolymer system.
This result was confirmed by molecular modeling of this system [132], which
showed that the longitudinal displacement of the conjugated backbones by 1–2 Å
changes the electronic coupling mediating hole hopping by over one order of
magnitude. Interestingly, these subtle structural changes have clear fingerprints in
X-ray diffraction patterns and
1 H NMR chemical shifts, which allow refining the
structural parameters down to the molecular scale. From this study, it was concluded that the unprecedented hole carrier mobilities observed in fibers of the
CDT-BTZ copolymers arise from a close packing of the polymer chains into a
close-to-registry assembly, providing optimal wavefunction overlap, together with
the intrinsically higher electronic bandwidth for charge motion along the chains.
This arrangement is primarily triggered by van der Waals interactions between the
long, linear alkyl chains and not by electrostatic donor–acceptor interactions. This
rather unexpected result emphasizes how important the detailed information on the
packing provided by a multi-technique approach including solid state NMR is to
obtain unbiased structural details, which are needed to optimize the structure for
specific applications.
5 Conclusion
Following the pioneering work of Hermann Staudinger [1], advances in the synthesis, characterization, and understanding of macromolecular and supramolecular
systems have led to an enormous variety and complexity in the field of polymer
science [89]. The traditional separation in terms of structure versus dynamics,
crystalline versus amorphous, or experiment versus theory is increasingly being
overcome. As far as characterization of such materials is concerned, no experimental or theoretical/simulation approach alone can provide full information. Instead, a
combination of techniques is called for and conclusions should be backed by results
provided by as many complementary methods as possible [27]. As demonstrated in
this contribution, the information provided by NMR and EPR is often indispensable
and unique. Combining scattering or MR spectroscopy with computer simulation is
well established today in the study of the structure and dynamics of biomacromolecules and provides new insight in the emerging field of partially disordered
proteins [64]. The examples described here show the power of such an approach
involving the combination of spectroscopy, scattering, and computer simulation in
the supramolecular field.
Last, but not least, the development of NMR spectroscopy is far from complete
[133]. In particular, in order to meet the ever-increasing demands of miniaturization, the sensitivity of NMR spectroscopy has to be increased substantially and
several approaches in response to that challenge are underway [134–137], down to
the detection of single spins [138]. Remarkably, in this area the combination of
316
H.W. Spiess
rather unravels the complexity of this remarkable CDT-BTZ copolymer system.
This result was confirmed by molecular modeling of this system [132], which
showed that the longitudinal displacement of the conjugated backbones by 1–2 Å
changes the electronic coupling mediating hole hopping by over one order of
magnitude. Interestingly, these subtle structural changes have clear fingerprints in
X-ray diffraction patterns and
1 H NMR chemical shifts, which allow refining the
structural parameters down to the molecular scale. From this study, it was concluded that the unprecedented hole carrier mobilities observed in fibers of the
CDT-BTZ copolymers arise from a close packing of the polymer chains into a
close-to-registry assembly, providing optimal wavefunction overlap, together with
the intrinsically higher electronic bandwidth for charge motion along the chains.
This arrangement is primarily triggered by van der Waals interactions between the
long, linear alkyl chains and not by electrostatic donor–acceptor interactions. This
rather unexpected result emphasizes how important the detailed information on the
packing provided by a multi-technique approach including solid state NMR is to
obtain unbiased structural details, which are needed to optimize the structure for
specific applications.
5 Conclusion
Following the pioneering work of Hermann Staudinger [1], advances in the synthesis, characterization, and understanding of macromolecular and supramolecular
systems have led to an enormous variety and complexity in the field of polymer
science [89]. The traditional separation in terms of structure versus dynamics,
crystalline versus amorphous, or experiment versus theory is increasingly being
overcome. As far as characterization of such materials is concerned, no experimental or theoretical/simulation approach alone can provide full information. Instead, a
combination of techniques is called for and conclusions should be backed by results
provided by as many complementary methods as possible [27]. As demonstrated in
this contribution, the information provided by NMR and EPR is often indispensable
and unique. Combining scattering or MR spectroscopy with computer simulation is
well established today in the study of the structure and dynamics of biomacromolecules and provides new insight in the emerging field of partially disordered
proteins [64]. The examples described here show the power of such an approach
involving the combination of spectroscopy, scattering, and computer simulation in
the supramolecular field.
Last, but not least, the development of NMR spectroscopy is far from complete
[133]. In particular, in order to meet the ever-increasing demands of miniaturization, the sensitivity of NMR spectroscopy has to be increased substantially and
several approaches in response to that challenge are underway [134–137], down to
the detection of single spins [138]. Remarkably, in this area the combination of
316
H.W. Spiess