those in the previous row structures. A model can be drawn that is based on linking
of the dimer to an extended row. This model is positioned onto the surface with the
carboxylate groups positioned on top of the surface calcium ions. Despite this
simple approach, the model fits excellently in size, in periodic repeat distance,
and in the observed orientation on the surface. These three structural features
together corroborate the model of a further linking of the dimer units into a zigzag
polymer.
Considering the basic dimer units suggests that a second structure is feasible
when linking the dimer building blocks, namely a closed ring. This structure is
observed experimentally, as shown in Fig. 72c. The size of the ring-like structures
fits excellently in size with a structure that is composed by further linking of the
dimer molecules via cleavage of the chlorine–phenyl bond. Arranging the model
such that the carboxylate groups can bind towards the calcium cations results in a
well-defined angle with respect to the underlying substrate, which is exactly what is
observed experimentally.
Thus, a two-step linking reaction was achieved by a sequential and selective
activation of two reaction sites. Extended zigzag and closed ring structures were
created upon sequential activation of homolytic cleavage of, first, the
bromine–phenyl bonds and, second, the chlorine–phenyl bonds.
To conclude, we have demonstrated a proof-of-principle reaction of the covalent
coupling of halide-substituted benzoic acid molecules on a bulk insulator, namely
calcite(10.4). Depending on the number and position of the halide substitution, we
can rationally design the structure of the resulting conjugated oligomers.
As a second step, we explored the possibility of a two-step polymerization
reaction to enhance the structural control necessary to arrive at complex polymer
architectures. By carefully selecting a precursor monomer that provides the
encoding of the selective and sequential reaction sites, we rationally controlled a
hierarchical two-step reaction process.
On-surface synthesis is expected to enhance variability when aiming at structure
formation on surfaces. First, on-surface synthesis allows the creation of polymeric
structures that might not be accessible from solution synthesis due to poor solubility.
Second, larger structures that are difficult to transfer onto a supporting surface can be
fabricated directly on the surface of interest, greatly facilitating the fabrication
process. Third, due to the confinement of the molecular building blocks onto the
2D surface, fundamental new reaction pathways might be envisioned, providing
further means for extending the structural complexity.
References
1. Vo ¨gtle F (2001) Dendrimers III – design, dimension, function. In: Houk KN, de Meijere A,
Kessler H, Lehn I-M, Ley SV, Schreiber SL, Thiem I, Trost BM (eds) Topics in current
chemistry, vol 212. Springer, Berlin
202
K. Binder et al.
of the dimer to an extended row. This model is positioned onto the surface with the
carboxylate groups positioned on top of the surface calcium ions. Despite this
simple approach, the model fits excellently in size, in periodic repeat distance,
and in the observed orientation on the surface. These three structural features
together corroborate the model of a further linking of the dimer units into a zigzag
polymer.
Considering the basic dimer units suggests that a second structure is feasible
when linking the dimer building blocks, namely a closed ring. This structure is
observed experimentally, as shown in Fig. 72c. The size of the ring-like structures
fits excellently in size with a structure that is composed by further linking of the
dimer molecules via cleavage of the chlorine–phenyl bond. Arranging the model
such that the carboxylate groups can bind towards the calcium cations results in a
well-defined angle with respect to the underlying substrate, which is exactly what is
observed experimentally.
Thus, a two-step linking reaction was achieved by a sequential and selective
activation of two reaction sites. Extended zigzag and closed ring structures were
created upon sequential activation of homolytic cleavage of, first, the
bromine–phenyl bonds and, second, the chlorine–phenyl bonds.
To conclude, we have demonstrated a proof-of-principle reaction of the covalent
coupling of halide-substituted benzoic acid molecules on a bulk insulator, namely
calcite(10.4). Depending on the number and position of the halide substitution, we
can rationally design the structure of the resulting conjugated oligomers.
As a second step, we explored the possibility of a two-step polymerization
reaction to enhance the structural control necessary to arrive at complex polymer
architectures. By carefully selecting a precursor monomer that provides the
encoding of the selective and sequential reaction sites, we rationally controlled a
hierarchical two-step reaction process.
On-surface synthesis is expected to enhance variability when aiming at structure
formation on surfaces. First, on-surface synthesis allows the creation of polymeric
structures that might not be accessible from solution synthesis due to poor solubility.
Second, larger structures that are difficult to transfer onto a supporting surface can be
fabricated directly on the surface of interest, greatly facilitating the fabrication
process. Third, due to the confinement of the molecular building blocks onto the
2D surface, fundamental new reaction pathways might be envisioned, providing
further means for extending the structural complexity.
References
1. Vo ¨gtle F (2001) Dendrimers III – design, dimension, function. In: Houk KN, de Meijere A,
Kessler H, Lehn I-M, Ley SV, Schreiber SL, Thiem I, Trost BM (eds) Topics in current
chemistry, vol 212. Springer, Berlin
202
K. Binder et al.