STM Study of Gold(I) Pyrazolates: Distinct Morphologies,
Layer Evolution, and Cooperative Dynamics
The MIT Faculty has made this article openly available. Please share
how this access benefits you. Your story matters.
Citation
Den Boer, Duncan, Markrete Krikorian, Birgit Esser, and Timothy
M. Swager. “STM Study of Gold(I) Pyrazolates: Distinct
Morphologies, Layer Evolution, and Cooperative Dynamics.” The
Journal of Physical Chemistry C 117, no. 16 (April 25, 2013):
8290–8298.
As Published
http://dx.doi.org/10.1021/jp4014493
Publisher
American Chemical Society (ACS)
Version
Author's final manuscript
Accessed
Wed May 25 20:53:02 EDT 2016
Citable Link
http://hdl.handle.net/1721.1/86149
Terms of Use
Article is made available in accordance with the publisher's policy
and may be subject to US copyright law. Please refer to the
publisher's site for terms of use.
Detailed Terms
The Journal of Physical Chemistry
STM Study of Gold(I) Pyrazolates: Distinct Morphologies,
Layer Evolution, and Cooperative Dynamics
Journal:
Manuscript ID:
Manuscript Type:
Date Submitted by the Author:
Complete List of Authors:
The Journal of Physical Chemistry
jp-2013-014493.R1
Article
n/a
den Boer, Duncan; Massachusetts Institute of Technology, Chemistry
Krikorian, Markrete; Massachusetts Institute of Technology, Chemistry
Esser, Birgit; University of Bonn, Department of Chemistry
Swager, Timothy; Mass. Inst. of Tech., Chemistry; Massachusetts Institute
of Technology, Department of Chemistry 18-597
ACS Paragon Plus Environment
Page 1 of 32
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
The Journal of Physical Chemistry
STM Study of Gold(I) Pyrazolates: Distinct
Morphologies, Layer Evolution, and Cooperative
Dynamics
Duncan den Boer, Markrete Krikorian, Birgit Esser, and Timothy M. Swager*
Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue,
Cambridge, Massachusetts 02139
E-mail: tswager@mit.edu
ABSTRACT
We describe the first study of trinuclear gold(I) pyrazolates on the molecular level by timedependent Scanning Tunneling Microscopy (STM). On the graphite/1-octanoic acid interface
dodecyl functionalized gold pyrazolates formed concentration-controlled morphologies. We
found two types of monomeric packing and one dimeric type with two trinuclear gold
pyrazolates next to each other on the surface. For an octadecyl functionalized derivative all
studied concentrations resulted in a dimeric morphology. However, different concentrations led
to different transient states during the layer evolution. At low concentrations, a transient
monomeric state was present with the alkyl chains in a gauche-conformation that subsequently
converted to a more optimized anti-conformation. At higher concentrations a less stable “line”
ACS Paragon Plus Environment
1
The Journal of Physical Chemistry
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Page 2 of 32
polymorph was observed. The confinement of the molecules to the surface led to cooperative
dynamics, in which two molecules in a dimer moved as if they were one particle. Furthermore, in
a higher level of cooperativity, the rotation of one dimer appears to induce rotations in coupled
neighboring dimers.
Keywords: molecular self-assembly, scanning probe microscopy, solid/liquid interface,
concentration, polymorphs, contrast
Introduction
The bottom-up creation of patterned surfaces by controlled self-assembly of molecules allows
molecular precision to be applied to emerging nanoscience and nanotechnology.1,2 For the
controlled construction of predictable and well-defined assemblies it is ideal to control the
specific adsorption of functional molecules at a surface,3 and understanding these assemblies on
the sub-molecular level will enable future designs. The necessary resolution for these studies is
provided by the Scanning Tunneling Microscope (STM), which can be operated under an
expanding range of conditions including the solid/liquid interface. A major advantage of a liquid
phase above the surface is that it acts as a reservoir of the functional molecules. This can allow
control of the morphology of a molecular monolayer by controlling the concentration of
functional molecules in the supernatant solution.4–9 Furthermore, the presence of the supernatant
solution assists in spontaneous dynamic processes such as diffusion and adsorption/desorption.
It is a continuing challenge to obtain a detailed understanding of the factors that control
complex and dynamic self-assembly processes.10,11 In this context, the study of spontaneous
dynamic processes at solid/liquid interfaces is of great interest, where molecules can be imaged
and the assembly is restricted by the reduced dimensionality. Examples of studies examining
ACS Paragon Plus Environment
2
Page 3 of 32
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
The Journal of Physical Chemistry
spontaneous molecular level dynamics include Ostwald ripening,12–14 desorption/readsorption
dynamics,15,16 conformational dynamics of single molecules,17 codeposition of solvent
molecules,18,19 and transitioning from metastable to thermodynamically more favored
polymorphs.20,21 In our studies we focused on the layer evolution and cooperative dynamics
occurring in monolayers.
This study is focused on trinuclear gold(I) pyrazolates, AuC12 and AuC18 (Fig. 1). Trimeric
gold complexes have been of interest since their discovery in 1970 by Vaughan.22 Their flat
shape makes them very suitable for assembly on a flat surface and their electronic, optical, and
chemical properties suggest utility as electronic materials and chemical sensors.23–27 Of special
interest in the context of our work is the possible implementation of these molecules in chemical
sensors. For example, carbon nanotube and graphene sensing devices generally require
functional molecules adsorbed to their surface to improve sensitivity and selectivity.28–31
Therefore, our study of molecular layers of trinuclear gold(I) pyrazolates on a graphite surface is
directed at gaining structural understanding to enable superior sensors.
The gold(I) pyrazolates AuC12 and AuC18 contain long alkyl chains that promote organized
assemblies of molecular layers on a graphite surface.32 It was expected that the molecular cores
indicated by the red triangle in Fig. 1 would play a role in the assembly process as a result of π-π
and metal-π interactions with the underlying graphite surface. We also anticipated a possible
favorable matching with the graphite lattice (illustrated in Fig. 1c).
ACS Paragon Plus Environment
3
The Journal of Physical Chemistry
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Page 4 of 32
Figure 1: a, b) Molecular structure of gold(I) pyrazolates AuC12 and AuC18. The red and yellow triangles indicate
the triangular-shaped molecular center and the three gold atoms. c) Schematic representation of the molecular core
including the gold atoms and an underlying graphite lattice, illustrating a possible favorable matching.
Results and Discussion
The gold(I) pyrazolates AuC12 and AuC18 were synthesized from the corresponding pyrazoles
through
reaction
with
[Au(SMe2)Cl]
as
shown
in
Scheme 1. 3 and 5 are accessible in two steps from acetyl acetone (1). Self-assembled
monolayers of these gold complexes were studied by STM at the graphite/1-octanoic acid
interface. A 5–10 µl droplet of a solution of the compound was applied to a freshly cleaved
surface, and during the STM topography measurements the tip was immersed in the droplet.
Different results were obtained for AuC12 and AuC18, as will be described below.
ACS Paragon Plus Environment
4
Page 5 of 32
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
The Journal of Physical Chemistry
Scheme 1. Synthesis of the trinuclear gold complexes AuC12 and AuC18.
ACS Paragon Plus Environment
5
The Journal of Physical Chemistry
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Page 6 of 32
AuC12: Concentration Dependent Morphologies
The self-assembly behavior of AuC12 was studied at different concentrations and generates
distinct morphologies on the surface. These morphologies correspond to stable phases, with
layers being monitored for at least four hours and often for more than 15 hours. The layers
typically formed within minutes after the application of the droplet, and the corresponding
concentration dependent morphology was observed immediately (Fig. 2a). This does not
preclude a transient morphology, but simply means that any intermediate morphology was not
stable long enough to be observed on the STM time scale, which is several minutes to obtain a
topography measurement.
AuC12 at Low Concentrations
For concentrations of 1 × 10-6 M and lower a morphology was found wherein the molecules of
AuC12 packed in a monomeric fashion and the functional centers of the molecules (depicted by
the red triangles in Figs. 1 and 2) within each domain were oriented in the same direction, as
shown in Fig. 2b. The unit cell of this packing arrangement was found to be a = 3.2 ± 0.2 nm, b =
3.4 ± 0.2 nm, and γ = 59 ± 5º. The monolayer is dynamic with molecules switching direction
and, in the process, joining a neighboring domain. Fig. 2b shows an example wherein several
molecules switch direction between two sequential scan lines. The switching in this example
may be induced by the tip, although mild scanning conditions were used (Vbias = -950 mV and Iset
= 10 pA) to minimize these effects. A correlation average filtering procedure (see S.I.)
constructed from a high resolution STM topography image shows the pyrazolate groups
surrounding the center part containing the gold atoms and the alkyl groups on the surface (Fig.
2b, bottom panel). DFT calculations on this type of trinuclear gold complex show that the
molecular electrostatic potentials are centered on the gold atoms and in the center of the
ACS Paragon Plus Environment
6
Page 7 of 32
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
The Journal of Physical Chemistry
molecular core and are directed above and below the plane of the molecule.33,34 This explains the
bright feature observed at the center of the molecule. When counting the alkyl groups there
appear to be twelve in a unit cell, which is double the expected number for a single molecule of
AuC12 (see Fig. S1). This observation is explained by assuming a co-deposition of 1-octanoic
acid solvent molecules. Co-deposition of solvent molecules has previously been observed by
STM.18,19,35 This model is supported by the bright features in the measurement highlighted by the
red circle in the center image of Fig. 2b. It has previously been shown that acid groups can
produce bright features in STM topography measurements.36,37 Also in line with this
interpretation is the area of the unit cell, which is 9.3 ± 1.6 nm2. The area of one molecule of
AuC12 adsorbed to a graphite surface is estimated to be 4.7 nm2,38 which leaves 4.6 ± 1.6 nm2
for the six co-adsorbed octanoic acid molecules. The area of one octanoic acid molecule would
be roughly 0.5 nm2, which indicates that there is indeed sufficient space on the surface for coadsorption and that this can therefore explain the “additional” observed alkyl chains. A
molecular model is constructed including co-adsorbed octanoic acid molecules (depicted in
blue), and is depicted in the bottom panel in Fig. 2b. It cannot be unambiguously determined
which alkyl groups belong to AuC12 and which to co-adsorbed solvent molecules, and therefore
the proposed molecular model acts as a suggestion in this regard.
ACS Paragon Plus Environment
7
The Journal of Physical Chemistry
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Page 8 of 32
Figure 2: Concentration controlled polymorphs of AuC12. a) Overview of the final states. b) Polymorph with the
monomers in the same direction. Top: STM topography, the unit cell is drawn: a = 3.2 ± 0.2 nm, b = 3.4 ± 0.2 nm, γ
= 59 ± 5º. The red and yellow ovals indicate two separate domains with different directions of the functional centers.
Inset: magnification, showing molecules changing direction between two scan lines. Center: correlation average.
The red and yellow triangles indicate the molecular center and the gold atoms. The red circle indicates a bright
feature that could correspond to the COOH group of a co-deposited 1-octanoic acid molecule. Bottom: proposed
corresponding molecular model, the unit cell is drawn. Co-adsorbed 1-octanoic acid molecules are indicated in
blue.c) Polymorph with the monomers in alternate directions. Top: STM topography, overview. Center: correlation
ACS Paragon Plus Environment
8
Page 9 of 32
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
The Journal of Physical Chemistry
average, the unit cell is drawn: a = 2.6 ± 0.1 nm, b = 5.3 ± 0.2 nm, γ = 66 ± 10º. Inset: different correlation average
with contrast optimized to observe alternate directions of centers. Bottom: proposed corresponding molecular model,
the unit cell is drawn. One molecule is indicated in red. d) Dimeric polymorph. Top: STM topography, overview.
The red circle indicates a single molecule, yellow ovals indicate dimers. Center: high resolution STM topography,
the unit cell is drawn: a = 3.2 ± 0.1 nm, b = 3.9 ± 0.1 nm, γ = 65 ± 7º. Bottom: proposed corresponding molecular
model, the unit cell is drawn. One molecule is indicated in red.
AuC12 at Medium Concentrations
For concentrations between 5 × 10-6 M and 4 × 10-5 M, the molecules of AuC12 adopt a
different packing. The unit cell of this packing contains two AuC12 molecules pointing in
different directions (see the inset of the center panel in Fig. 2c) and has dimensions a = 2.6 ± 0.1
nm, b = 5.3 ± 0.2 nm, and g = 66 ± 10º (Fig. 2c). The area per molecule is 6.3 ± 1.0 nm2, a value
smaller than that found in the packing at lower concentrations. A molecular model, constructed
from the STM measurements, is depicted in the bottom panel of Fig. 2c. It shows a monomeric
packing with the cores of the two AuC12 molecules in the unit cell pointing in opposite
directions. Per molecule of AuC12 there is room for approximately three co-adsorbed 1-octanoic
acid molecules.
AuC12 at High Concentrations
A dimeric packing of AuC12 was observed when the concentrations are between 4 × 10-5 M
and 1 × 10-3 M (Fig. 2d). In this morphology the molecules displayed an ordered structure, in
which molecular dimers appeared, as are indicated by the yellow ovals in the topmost panel of
Fig. 2d. The unit cell for this packing was found to be a = 3.2 ± 0.1 nm, b = 3.9 ± 0.1 nm, and γ =
65 ± 7º and contains two molecules of AuC12. This structure is not due to a “double tip” artifact,
as confirmed by the observance of a single molecule of AuC12 next to a hole in the layer
(indicated by the red circle in the topmost panel of Fig. 2d). A correlation average of a high
resolution topography measurement reveals the orientation of the molecular cores that are
highlighted by the gold atoms and also the alkyl chains on the surface (center panel of Fig. 2d).
ACS Paragon Plus Environment
9
The Journal of Physical Chemistry
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Page 10 of 32
In this case the center of the molecular core does not show up as one bright spot, but there are
individual spots that relate to the gold atoms in the molecular core. This difference is probably
due to the specific tip geometry (as with different tips the dimeric morphology also had a single
bright spot in the center of the molecular core). The STM topography measurements suggest a
molecular model (bottom panel of Fig. 2d). An individual molecule of AuC12 in this dimer
packing has an area of 5.7 ± 0.6 nm2, lower than the values for the other two observed packings.
This indicates that this morphology has the highest molecular density on the surface, nicely
correlating with the higher density of molecules in the supernatant solution.
It is interesting to note that at an AuC12 concentration of 4 × 10-5 M in 1-octanoic acid, the
dimeric morphology coexists with the monomer morphology, in which the centers point in
alternate directions. This reproducible state was also found to be stable, with a constant relative
abundance as long as 16.5 hours after the start of the experiment. The large error bars in Fig. 2a
are the result of larger domain sizes than the scan size of the STM topography measurement, i.e.
> 200 nm, and therefore within an STM scan only one of the two packings was observed.
Higher concentrations of AuC12 are not included in Fig. 2a as in that case the solution formed
a gel. To apply a droplet to the surface involved heating, and therefore the exact concentration
during the STM measurements was undetermined. Fig. S3 shows a short-lived “line” packing
that was observed as a transient state in this concentration regime. The final state under these
conditions was the dimeric packing.
AuC18: Layer Evolution and Transient Morphologies
Molecular layers of AuC18 on the graphite/1-octanoic acid interface display significant
differences from those of AuC12. Although different AuC12 concentrations gave different
morphologies on the surface, for AuC18 all concentrations in the studied range of 1 × 10-6–1 ×
ACS Paragon Plus Environment
10
Page 11 of 32
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
The Journal of Physical Chemistry
10-3 M resulted in a dimeric packing within two hours after the start of the experiment (Fig. 3a).
In contrast to AuC12, we observed concentration dependent transient morphologies during the
layer evolution.
ACS Paragon Plus Environment
11
The Journal of Physical Chemistry
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Page 12 of 32
Figure 3: Layer evolution of AuC18. a) Overview of the final states. b) Low concentrations: monomeric packing
to dimeric packing. First panel: STM topography of patches of monomeric packing on the surface. Second panel:
monomeric packing with non-straight alkyl chains 30–45 minutes after the start of the experiment. Red and yellow
arrows point at identically ordered alkyl chains. Third panel: monomeric packing with straight alkyl chains 1 h after
the start of the experiment. The unit cell is drawn: a = 4.2 ± 0.1 nm, b = 6.7 ± 0.1 nm, γ = 52 ± 5º. Fourth panel:
proposed corresponding molecular model, the unit cell is drawn. One molecule is indicated in red. c) Medium
ACS Paragon Plus Environment
12
Page 13 of 32
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
The Journal of Physical Chemistry
concentration: dimeric packing. Top: STM topography, overview. Angle α denotes the angle between the two
domains. The red circle indicates a single molecule, yellow ovals indicate dimers. Center: high resolution STM
topography image, the unit cell is drawn: a = 4.0 ± 0.1 nm, b = 4.3 ± 0.2 nm, γ = 63 ± 7º. The yellow dashed line
follows a main symmetry axis of the underlying graphite, the solid yellow line runs perpendicular to this and is a
reference axis for the propagation axis, denoted by the red line. Ф is the angle between the reference axis and the
propagation axis. The circles represent non-covered parts of the surface. Bottom: proposed corresponding molecular
model, the unit cell is drawn. One molecule is indicated in red. d) “Line” polymorph coexisting with dimeric
polymorph, ending in dimeric polymorph. Top: STM topography, overview. Center: Correlation average, the unit
cell is drawn: a = 3.2 ± 0.2 nm, b = 8.9 ± 0.2 nm, γ = 76 ± 10º. Bottom: proposed corresponding molecular model,
the unit cell is drawn. One molecule is indicated in red.
AuC18 at Medium Concentrations
Intermediate concentrations (5 × 10-5 M) of AuC18 in 1-octanoic acid did not display transient
morphologies, and a dimeric morphology was formed within minutes after the application of the
droplet. This dimeric morphology has a unit cell of a = 4.0 ± 0.1 nm, b = 4.3 ± 0.2 nm, and γ =
63 ± 7º (Fig. 3c). Accordingly, every molecule of AuC18 covers an area of 7.7 ± 1.0 nm2, and it
is confirmed that this is not due to a “double tip” artifact, as single features were also observed
next to holes or domain boundaries in the layer (indicated by the red circle in the top panel of
Fig. 3c). The high resolution STM topography image in the center panel of Fig. 3c clearly shows
the location of the molecular core with the individual gold atoms and the alkyl chains. Based on
the STM topography measurements a molecular model is constructed, as shown in the bottom
panel of Fig. 3c. The circles indicate small areas of the surface that are bare in the model, which
can be observed in the STM topography measurements.
Chirality of AuC18 Dimeric Packing
The adsorption to a surface often leads to chiral motifs in a monolayer, even in achiral
molecules.39 The dimeric packing of AuC18 is chiral, and molecular models of the two
enantiomeric domains together with the corresponding STM measurements of the observed
enantiomers are presented in Fig. 4. The difference between these two isomers that is the most
ACS Paragon Plus Environment
13
The Journal of Physical Chemistry
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Page 14 of 32
convenient to observe in the STM measurements is the direction of the alkyl tails indicated by
the red circles.
In fact, all of the observed molecular packings should be chiral, as all molecular layers with an
oblique unit cell share this property.40 However, an in-depth study of the chirality of all the
morphologies is beyond the scope of this paper, and we have limited ourselves to the dimeric
packing of AuC18 as an example.
Figure 4: Chirality of the dimeric packing of AuC18. Left and right show the two enantiomers observed for the
dimeric packing of AuC18. The red circles indicate the alkyl chains that assist in the identification of the isomer.
Insets: the corresponding proposed molecular models.
AuC18 at High Concentrations
At “high” concentrations (8 × 10-5–1 × 10-3 M), the dimeric morphology coexisted with a
“line” morphology at the start of the experiment, as depicted in Fig. 3d. Yet higher
concentrations of the solution led to the formation of a gel state, similar to what was found for
AuC12, and this concentration range was not studied. The unit cell for the “line” polymorph of
AuC18 was found to be: a = 3.2 ± 0.2 nm, b = 8.9 ± 0.2 nm, and γ = 76 ± 10º and contains four
molecules of AuC18. This morphology is less stable and therefore is hard to visualize by STM
with high resolution. A model based on a correlation average is depicted in the bottom panel of
ACS Paragon Plus Environment
14
Page 15 of 32
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
The Journal of Physical Chemistry
Fig. 3d. As the alkyl chains could so far not be visualized in detail, the model is constructed from
the locations and directions of the molecular cores that are visible in the STM image combined
with the determined values of the unit cell. The area per molecule for this polymorph
corresponds to 6.9 ± 0.9 nm2. This area is lower than for the dimeric morphology, which could
also be observed when the two polymorphs were present within one image. The higher molecular
density on the surface for the “line” polymorph compared to that of the dimeric polymorph
suggests that the “line” morphology will be favored at higher concentrations of the supernatant
solution. However, within two hours this morphology had typically been replaced by the dimeric
packing over the entire surface (both in scanned areas and remote areas that were previously
unscanned). Hence the dimeric packing is thermodynamically more stable.
AuC18 at Low Concentrations
An interesting transition in the evolution of the layer formation occurs at “low” concentrations
(1 × 10-6–3 × 10-5 M). In this range, the layer growth typically started as patches of a monomeric
packing (top panel Fig. 3b and Fig. S4) that grew over time. Intriguingly, in our research a
monomeric packing was observed that had many gauche segments of alkyl chains with initial
layer formation (within the first half hour, second panel of Fig. 3b). Generally, STM images
show alkyl chains in anti-conformations on the graphite surfaces, with optimal interactions with
the underlying graphite lattice. In the observed transient morphology the alkyl chains appear less
ordered. Even though at first glance there appears to be less order, the kinked alkyl chains are not
randomly oriented on the surface. This is highlighted by the red arrows and the yellow arrows,
both pointing at two alkyl chains in the same conformation. After approximately 15 minutes the
alkyl chains assume an anti-conformation. The values for the unit cell remained unchanged, a =
4.2 ± 0.1 nm, b = 6.7 ± 0.1 nm, γ = 52 ± 5º, and contains two AuC18 molecules. A molecular
ACS Paragon Plus Environment
15
The Journal of Physical Chemistry
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Page 16 of 32
model for this packing is proposed in the fourth panel of Fig. 3b. It is likely that there are
molecules of 1-octanoic acid co-adsorbed, as the experimentally determined area per molecule of
AuC18 in this packing is 11.1 ± 1.2 nm2, while an estimated value for the area of one molecule
of AuC18 is only 6.6 nm2.38 The observation of the transient kinked alkane polymorph suggests
that even with non-optimized interactions between the alkyl chains of AuC18 with the
underlying graphite, the molecule is still somewhat immobile. It is therefore proposed that the
molecular cores interact strongly with the underlying graphite. This could be explained by π-π
and Au-π interactions on the graphite surface (illustrated in Fig. 1c). The solid/liquid interface
dynamic processes present allow desorption and readsorption of the alkyl chains15,17 for the
transition to a more optimized anti-conformation. Such a conformation optimizes both the
interactions with the underlying graphite as well as with the neighboring alkyl chains.
The layer evolution at “low” concentrations involves a coexistence of the monomeric packing
with the dimeric packing (an example is given in Fig. 5d), subsequently leading exclusively to
the dimeric packing (typically 1.5 hours after the observation of the first patches of monomeric
packing). This dimeric packing was also present in regions of the surface that were previously
unscanned, indicating that this transition was not caused by the scanning or the presence of the
STM tip.
The monomeric packing at “low” concentration range has a unit cell containing two molecules,
similar to the monomeric morphology of AuC12 with the functional centers pointing in alternate
directions.
Comparing AuC12 and AuC18 assembly
Our STM measurements suggest some general difference in the assembly of AuC18 and
AuC12. The monomeric packing of AuC18 having kinked alkanes is likely formed as a result of
ACS Paragon Plus Environment
16
Page 17 of 32
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
The Journal of Physical Chemistry
longer alkyl groups that immobilized the compound even with non-optimized interactions with
the underlying graphite. Also, for the study of the evolution of layer formation, longer alkyl
chains slow down the self-assembly process, which enabled us to visualize transient states. The
observation that the molecules of AuC18 have a dimeric equilibrium packing in this
concentration range suggests that this packing is thermodynamically more favorable. When
comparing the packings for AuC12 to the packings for AuC18, we can see that due to the longer
alkyl groups, a monomeric packing of AuC18 leads to a larger porosity on the surface (i.e. there
is more “uncovered” graphite area) than a monomeric packing of AuC12. Also, the dimeric
packing for AuC18 leads to only a very small part of the surface being uncovered (indicated by
circles in Fig. 3c) while for the dimeric packing of AuC12 there are still uncovered parts present
(as can be seen in the high resolution STM measurements depicted in Fig. 2c). The difference
between the porosity of the different packings of AuC18 is therefore larger than for the different
packings of AuC12, which would therefore lead to a driving force for the molecular layer to
transform to the dimeric packing of AuC18.
ACS Paragon Plus Environment
17
The Journal of Physical Chemistry
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Page 18 of 32
Contrast Differences in STM Topography
An interesting aspect of the molecular layers is revealed by comparing the apparent heights of
the trimeric gold complexes on the surface. Fig. 5a and S8 show a molecular layer of AuC12 in
the monomeric morphology with the functional centers pointing in alternate directions. Fig. 5b
shows a cross-section. As is apparent from the cross-section, the two molecules of AuC12 in the
unit cell have different apparent heights, i.e. one of the two rows appears higher than the other by
approximately 50%.
A similar effect is also observed when the apparent height of molecules of AuC18 in the
monomeric packing is compared to the dimeric packing (Figs. 5c and d). The molecules in the
monomeric packing appear about 50% higher. This cannot be explained by a change in the tip, as
both cross-sections are done in the same scan lines with the same tip. This difference in contrast
is clearly apparent in the inset of Fig. 5c. Two molecules (indicated by the red circle) appear to
be a dimer. However, according to the contrast, only the right one is in the dimeric packing,
while the left one has the same contrast as the surrounding molecules of AuC18 in the
monomeric packing.
ACS Paragon Plus Environment
18
Page 19 of 32
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
The Journal of Physical Chemistry
Figure 5: Contrast differences. a) Correlation average constructed from an STM topography of molecules of
AuC12 in a monomeric packing with the centers in alternate directions b) Cross-section corresponding to the dashed
line in (a). c) Molecular layer of molecules of AuC18 coexisting in a monomeric morphology and a dimeric
morphology. Inset: magnification of (c). Red circle indicates an apparent dimer with different contrasts. d) Crosssections with the dashed trace corresponding to the dashed line in (c), and the solid trace corresponding to the solid
line in (c).
Crystal structures of non-alkylated trinuclear gold pyrazolates show that the molecule is
planar,33 and we expect that this is also the case on the graphite surface in the different molecular
packings and therefore that the observed contrast difference is not due to a difference in the
height of the molecular core. It has previously been shown that a difference in registry with an
underlying surface can lead to changes in contrast of molecules imaged by STM (and is
generally accepted as the cause of the often observed moiré patterns in a molecular layer on top
of graphite).36,41,42 In fact, some research groups use the difference in contrast as a way to
quantify the mismatch of adsorbed molecules with the registry of the underlying graphite.43 We
ACS Paragon Plus Environment
19
The Journal of Physical Chemistry
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Page 20 of 32
therefore propose that this is the explanation for the observed contrast differences for AuC12 and
AuC18. We speculate that for the molecules with a higher apparent height, the electronic
coupling with the underlying graphite is more favorable. An observation that seems to support
this is that the molecules of AuC12 in the monomeric morphology with the molecular cores
pointing in alternate directions with lower apparent height also appear to be more mobile and
hence, only weakly bound to the surface (see Fig. S2).
Cooperative Dynamics of AuC18 Dimers
In addition to the layer evolution, other dynamic effects were also studied by time-dependent
STM. Cooperative dynamic processes were observed during the monitoring of molecular layers
of AuC18 in the dimeric packing. Two molecules of an AuC18 dimer were regularly observed to
move in a cooperative fashion such that the dimer appeared to rotate on the surface as if it were a
single particle. An example is given in Fig. 6a, wherein one dimer (indicated by the yellow circle
in the magnification) is pointing vertically in the first STM topography measurement, and three
minutes later the same dimer is pointing horizontally. It is not expected that the molecules of
AuC18 forming a dimer have an attractive interaction with each other. Lateral dimers do not
exist in solution but form as a result of the underlying graphite surface. It is proposed that even
though there is no specific attractive interaction expected between two members of a dimer, there
still is a favorable geometric fit for two of the molecules to be in close proximity, which leads to
a “gearing” or coupling of the rotational dynamics.
ACS Paragon Plus Environment
20
Page 21 of 32
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
The Journal of Physical Chemistry
Figure 6: Cooperative dynamics: rotations of AuC18 dimers. a) Two subsequent STM topography measurements
with a time interval of three minutes of a layer of AuC18 in the dimeric morphology. White arrows indicate the slow
scan direction. Insets: Magnification of the area of interest. The rotation of a single dimer of AuC18 is indicated by
the yellow circles. b) Subsequent STM topography measurements with a time interval of three minutes showing
several subsequent rotations of dimers of AuC18. White arrows indicate the slow scan direction. In the first images
the yellow ovals indicate two dimers that rotate at the same time. The red circles indicate a nearby dimer rotating as
well. The yellow arrows point at a dimer that was rotated for several scan lines, then rotates back, after which the
other dimers also return to their original orientation. c) STM topography image of AuC18 in the dimeric
morphology, illustrating the disruption of the layer by a dimer in a different orientation (indicated by the yellow
circle). d) Subsequent STM topography images with a time interval of three minutes, showing the change of
orientation of a whole domain of dimers of AuC18. White arrows indicate the slow scan direction. The orientation
of the domain is indicated by the dashed yellow lines. The yellow circle indicates an area with seemingly less
immobilized dimers.
Beyond the cooperative movement of the two molecules in a dimer, a higher level of
cooperativity was also observed. It appears that a dimer’s rotation can induce neighboring dimers
to rotate as well as illustrated in Fig. 6b. In the first images the yellow ovals indicate two dimers
rotating simultaneously (in the same time interval between being imaged by the STM). These
rotations appear to induce a nearby dimer to rotate as indicated by the red circles. After several
ACS Paragon Plus Environment
21
The Journal of Physical Chemistry
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Page 22 of 32
minutes a dimer nearby is rotated for a short amount of time (imaged for a few scan lines,
indicated by the yellow arrow), after which the dimer returns to its original orientation. This is
then followed by the other rotated dimers to rotate again and return to their original orientation.
A more extreme example of such cooperative rotation can be seen in Fig. 6d. Here a whole
domain of dimers of AuC18 changes its orientation three times in a row. The yellow circle
indicates an area where after this final rotation the dimers of AuC18 have a “blurry” signature.
This is possibly the result of dimers moving on a time scale too fast for STM visualization. This
is not a tip artifact, since in the right part of the image (next to the yellow circle) this effect is not
seen, even though these molecules are imaged by the same tip (as the fast scan direction is
horizontal).
Such a cooperative effect of a whole domain is a surprising phenomenon. We think that several
factors might be involved to facilitate such an effect.
1) In Fig. 6a the rotation starts at a domain boundary. At such boundaries, molecules are often
less immobilized than in the center of a domain. Also in Fig. 6d, a domain boundary is nearby
the domain that changes direction.
2) These rotations might be facilitated by the fact that the unit cell is not square. This
asymmetry disrupts the surrounding dimers in the monolayer and introduces local strain. An
STM topography image (Fig. 6c) shows a dimer of AuC18 molecules (yellow circle) that has a
different orientation and disrupts the dimers surrounding it. The disruption in the layer makes it
more favorable for a nearby dimer to also rotate.
3) The solid/liquid interface allows for dynamic processes such as desorption and readsorption
of the alkyl chains.15,17 It is also important to realize that the molecules as a whole can stay
adsorbed to the surface during the rotation.
ACS Paragon Plus Environment
22
Page 23 of 32
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
The Journal of Physical Chemistry
4) In the observed contrast differences in Fig. 5, our hypothesis is that a bright contrast is
related to a more favorable coupling to the underlying surface. The dimeric packing of AuC18
was less bright than the monomeric packing, which might suggest a less favorable coupling to
the graphite and therefore might be less immobilized. This is consistent with the observation that
such dimers can rotate on the surface.
5) It is possible that the rotations are influenced by the STM tip and are not completely
spontaneous. However, varying the scanning parameters (Vbias, Iset, scan speed and scan angle) in
an attempt to induce these dynamics has so far proven unsuccessful
6) It is important to realize that the rotations in Fig. 6d appear to have occurred simultaneously,
but that this is within the time resolution of three minutes. We expect there to be a sequence of
events, similar to Fig. 6b.
Conclusion
Trinuclear gold complexes form organized assemblies on the surface of graphite. For their
implementation in devices involving a molecular surface layer, it is important to understand the
processes present during the molecular self-assembly. This is true not only for these molecules,
but for other functional molecules as well, and our findings are therefore relevant in a more
general sense.
We described herein studies of two trinuclear gold complexes, AuC12 and AuC18, by
Scanning Tunneling Microscopy at the solid/liquid interface. Molecules of AuC12 were found to
form distinct morphologies (monomeric and dimeric) on the graphite surface, depending on the
concentration of the solution. For AuC18 the results were different: in the studied concentration
range all layers ended up in the same dimeric morphology. Using time-dependent STM studies it
was possible to study the layer evolution on the molecular level, and different transient
ACS Paragon Plus Environment
23
The Journal of Physical Chemistry
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Page 24 of 32
morphologies were present at different concentrations. At lower concentrations a morphology
was observed in the early assembly process that did not have the characteristic “straight alkyl
chain” morphology that is typically observed in STM measurements, but instead the alkyl chains
had a kinked gauche conformation. Still, there was order present in this morphology with a unit
cell containing two molecules of AuC18. Over time these alkyl chains converted to an anticonformation. It is proposed that the non-optimized kinked structure is a kinetic state and that the
functional centers of the molecules have an interaction with the underlying graphite and play a
role in the early stages of assembly.
Contrast differences between the different morphologies and also between molecules within
one morphology were observed and proposed to be caused by a different registry of the
molecules with the underlying graphite.
Finally, it was observed that molecules of AuC18 in a dimeric morphology on the surface can
move in a cooperative fashion in such a way that a dimer appears to rotate as if it were a single
particle. In a higher level of cooperativity such rotations seem to induce nearby dimers to rotate
as well, which can go as far as a whole domain of dimers of AuC18 changing orientation. It is
important to realize that in specific circumstances a small variation (the rotation of one dimer)
can have an amplified effect. For the implementation of functional molecules in devices such
insights in the self-assembly processes can give handles to control the final morphology of the
layer.
Acknowledgement
This research was supported by the National Science Foundation (DMR-1005810), Air Force
Office of Scientific Research (FA9550-10-1-0395) with the purchase of an AFM/STM system,
ACS Paragon Plus Environment
24
Page 25 of 32
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
The Journal of Physical Chemistry
the Center for Excitonics and Energy Frontier Research Center funded by the Department of
Energy, Office of Basic Energy Sciences (DF-SC0001088), a Marie Curie International
Outgoing Fellowship within the 7th European Community Framework Programme for D.d.B
(273837), and a postdoctoral fellowship by the German Academy of Sciences for B.E. (LPDS
2009-8).
Supporting Information Available
Experimental and synthetic procedures, scanning parameters for the figures, and additional STM
measurements are included. This material is available free of charge via the Internet at
http://pubs.acs.org/.
ACS Paragon Plus Environment
25
The Journal of Physical Chemistry
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Page 26 of 32
References
1) Lehn, J.-M. Toward complex matter: Supramolecular chemistry and self-organization.
Proc. Nat. Acad. Sci. 2002, 99, 4763–4768.
2) Whitesides, G. M.; Boncheva, M. Beyond molecules: Self-assembly of mesoscopic and
macroscopic components. Proc. Nat. Acad. Sci. 2002, 99, 4769–4774.
3) Barth, J. V.; Costantini, G.; Kern, K. Engineering atomic and molecular nanostructures at
surfaces. Nature 2005, 437, 671–679.
4) Lei, S.; Tahara, K.; De Schryver, F. C.; Van der Auweraer, M.; Tobe, Y.; De Feyter, S.
One Building Block, Two Different Supramolecular Surface-Confined Patterns:
Concentration in Control at the Solid–Liquid Interface. Angew. Chem. 2008, 120, 3006–
3010; Angew. Chem. Int. Ed. 2008, 47, 2964–2968.
5) Kampschulte, L.; Werblowsky, T. L.; Kishore, R. S. K.; Schmittel, M.; Heckl, W. M.;
Lackinger, M. Thermodynamical Equilibrium of Binary Supramolecular Networks at the
Liquid-Solid Interface. J. Am. Chem. Soc. 2008, 130, 8502–8507.
6) Ciesielski, A.; Schaeffer, G.; Petitjean, A.; Lehn, J.-M.; Samorì, P. STM Insight into
Hydrogen-Bonded Bicomponent 1D Supramolecular Polymers with Controlled
Geometries at the Liquid-Solid Interface. Angew. Chem. 2009, 121, 2073–2077; Angew.
Chem. Int. Ed. 2009, 48, 2039–2043.
7) Ahn, S.; Matzger, A. J. Six Different Assemblies from One Building Block: TwoDimensional Crystallization of an Amide Amphiphile. J. Am. Chem. Soc. 2010, 132,
11364–11371.
8) Meier, C.; Roos, M.; Künzel, D.; Breitruck, A.; Hoster, H. E.; Landfester, K.; Gross, A.;
Behm, R. J.; Ziener, U. Concentration and Coverage Dependent Adlayer Structures:
ACS Paragon Plus Environment
26
Page 27 of 32
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
The Journal of Physical Chemistry
From Two-Dimensional Networks to Rotation in a Bearing. J. Phys. Chem. C 2010, 114,
1268–1277.
9) Zhang, X.; Chen, T.; Chen, Q.; Deng, G.-J.; Fan, Q.-H.; Wan, L.-J. One Solvent Induces
a Series of Structural Transitions in Monodendron Molecular Self-Assembly from
Lamellar to Quadrangular to Hexagonal. Chem. Eur. J. 2009, 15, 9669–9673.
10) Voigtlaender, B.; Karthaeuser, S.; Filimonov, S. N.; Tait, S. L. Bottom-Up Approaches
by Self-Organization Techniques. In Nanoelectronics and Information Technology; 3rd
Ed. Waser, R, Ed. Wiley-VCH: New York, 2012; pp 303-320.
11) Den Boer, D.; Coenen, M. J. J.; Elemans, J. A. A. W.; Speller, S. Scanning Tunneling
Microscopy of Chemistry at Solid-Liquid Interfaces. In Encyclopedia of Nanoscience and
Nanotechnology; Nalwa, H. S., Ed. American Scientific Publishers: Valencia, California,
2011; Vol. 22, pp 411-460.
12) Stabel, A.; Heinz, R.; De Schryver, F. C.; Rabe, J. P. Ostwald Ripening of TwoDimensional Crystals at the Solid-Liquid Interface. J. Phys. Chem. 1995, 99, 505–507.
13) Samorì, P.; Müllen, K.; Rabe, J. Molecular-Scale Tracking of the Self-Healing of
Polycrystalline Monolayers at the Solid-Liquid Interface. Adv. Mater. 2004, 16, 1761–
1765.
14) Florio, G. M.; Klare, J. E.; Pasamba, M. O.; Werblowsky, T. L.; Hyers, M.; Berne, B. J.;
Hybertsen, M. S.; Nuckolls, C.; Flynn, G. W. Frustrated Ostwald Ripening in SelfAssembled Monolayers of Cruciform π-Systems. Langmuir 2006, 22, 10003–10008.
15) Padowitz, D. F.; Messmore, B. W. STM Observations of Exchange Dynamics at the
Solid–Liquid Interface Using a Molecular Tracer. J. Phys. Chem. B 2000, 104, 9943–
9946.
ACS Paragon Plus Environment
27
The Journal of Physical Chemistry
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Page 28 of 32
16) Coenen, M. J. J.; Cremers, M.; Den Boer, D.; Van den Bruele, F.; Khoury, T.; Sintic, M.;
Crossley, M. J.; Van Enckevort, W. J. P.; Hendriksen, B. L. M.; Elemans, J. A. A. W. et
al. Little exchange at the liquid/solid interface: defect-mediated equilibration of
physisorbed porphyrin monolayers. Chem. Commun. 2011, 47, 9666–9668.
17) Xu, H.; Minoia, A.; Tomovic, Z.; Lazzaroni, R.; Meijer, E. W.; Schenning, A. P. H. J.;
De Feyter, S. A Multivalent Hexapod: Conformational Dynamics of Six-Legged
Molecules in Self-Assembled Monolayers at a Solid-Liquid Interface. ACS Nano 2009, 3,
1016–1024.
18) De Feyter, S.; Gesquière, A.; Abdel-Mottaleb, M. M.; Grim, P. C. M.; De Schryver, F.
C.; Meiners, C.; Sieffert, M.; Valiyaveettil, S.; Müllen, K. Scanning Tunneling
Microscopy: A Unique Tool in the Study of Chirality, Dynamics, and Reactivity in
Physisorbed Organic Monolayers. Acc. Chem. Res. 2000, 33, 520–531.
19) Gesquière, A.; Abdel-Mottaleb, M. M.; De Feyter, S.; De Schryver, F. C.; Sieffert, M.;
Müllen, K.; Calderone, A.; Lazzaroni, R.; Brédas, J. L. Dynamics in Physisorbed
Monolayers of 5-Alkoxy-isophthalic Acid Derivatives at the Liquid/Solid Interface
Investigated by Scanning Tunneling Microscopy. Chem. Eur. J. 2000, 6, 3739–3746.
20) Elemans, J. A. A.W.; Lensen, M. C.; Gerritsen, J.W.; Van Kempen, H.; Speller, S.; Nolte,
R. J. M.; Rowan, A. E. Scanning Probe Studies of Porphyrin Assemblies and Their
Supramolecular Manipulation at a Solid–Liquid Interface. Adv. Mater. 2003, 15, 2070–
2073.
21) Tahara, K.; Furukawa, S.; Uji-i, H.; Uchino, T.; Ichikawa, T.; Zhang, J.; Mamdouh, W.;
Sonoda, M.; De Schryver, F. C.; De Feyter, S.; Tobe, Y. Two-Dimensional Porous
ACS Paragon Plus Environment
28
Page 29 of 32
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
The Journal of Physical Chemistry
Molecular Networks of Dehydrobenzo[12]annulene Derivatives via Alkyl Chain
Interdigitation. J. Am. Chem. Soc. 2006, 128, 16613– 16625.
22) Vaughan, L. G. Organogold chemistry. III. 2-pyridylgold(I) J. Am. Chem. Soc. 1970, 92,
730–731.
23) Minghetti, G.; Banditelli, G.; Bonati, F. Metal Derivatives of Azoles. 3. The Pyrazolato
Anion (and Homologs) as a Mono- or Bidentate Ligand: Preparation and Reactivity of
Tri-, Bi-, and Mononuclear Gold(I) Derivatives. Inorg. Chem. 1979, 18, 658–663.
24) Burini, A.; Fackler, Jr., J. P.; Galassi, R.; Grant, T. A.; Omary, M. A.; RawashdehOmary, M. A.; Pietroni, B. R.; Staples, R. J. Supramolecular Chain Assemblies Formed
by Interaction of a π Molecular Acid Complex of Mercury with π-Base Trinuclear Gold
Complexes. J. Am. Chem. Soc. 2000, 122, 11264–11265.
25) White-Morris, R.; Olmstead, M.; Attar, S.; Balch, A. Intermolecular Interactions in
Polymorphs of Trinuclear Gold(I) Complexes: Insight into the Solvoluminescence of
AuI3(MeN=COMe)3. Inorg. Chem. 2005, 44, 5021–5029.
26) Kishimura, A.; Yamashita, T.; Aida, T. Phosphorescent Organogels via “Metallophilic”
Interactions for Reversible RGB–Color Switching J. Am. Chem. Soc. 2005, 127, 179–
183.
27) Gimeno, M. C. Modern Supramolecular Gold Chemistry; Wiley-VCH Verlag GmbH &
Co. KGaA, 2009; pp 1–63.
28) Kauffman, D. R.; Star, A. Carbon Nanotube Gas and Vapor Sensors. Angew. Chem.
2008, 120, 6652–6673; Angew. Chem. Int. Ed. 2008, 47, 6550–6570.
29) Schnorr, J. M.; Swager, T. M. Emerging Applications of Carbon Nanotube. Chem. Mater.
2011, 23, 646–657.
ACS Paragon Plus Environment
29
The Journal of Physical Chemistry
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Page 30 of 32
30) Liu, Y.; Dong, X.; Chen, P. Biological and chemical sensors based on graphene
materials. Chem. Soc. Rev. 2012, 41, 2283–2307.
31) Georgakilas, V.; Otyepka, M.; Bourlinos, A. B.; Chandra, V.; Kim, N.; Kemp, K. C.;
Hobza, P.; Zboril, R.; Kim, K. S. Functionalization of Graphene: Covalent and NonCovalent Approaches, Derivatives and Applications. Chem. Rev. 2012, 112, 6156–6214.
32) Qiu, X.; Wang, C.; Zeng, Q.; Xu, B.; Yin, S.; Wang, H.; Xu, S.; Bai, C. Alkane-Assisted
Adsorption and Assembly of Phthalocyanines and Porphyrins. J. Am. Chem. Soc. 2000,
122, 5550–5556.
33) Omary, M.; Rawashdeh-Omary, M.; Gonser, M.; Elbjeirami, O.; Grimes, T.; Cundari, T.
Metal Effect on the Supramolecular Structure, Photophysics, and Acid-Base Character of
Trinuclear Pyrazolato Coinage Metal Complexes. Inorg. Chem. 2005, 44, 8200-8210.
34) Tekarli, S. M.; Cundari, T. R.; Omary, M. A. Rational Design of Macrometallocyclic
Trinuclear Complexes with Superior π-Acidity and π-Basicity. J. Am. Chem. Soc. 2008,
130, 1669.
35) Vanoppen, P.; Grim, P. C. M.; Rücker, M.; De Feyter, S.; Moessner, G.; Valiyaveettil, S.;
Müllen, K.; De Schryver, F. C. Solvent Codeposition and Cis–Trans Isomerization of
Isophthalic Acid Derivatives Studied by STM. J. Phys. Chem. 1996, 100, 19636–19641.
36) Rabe, J. P.; Buchholz, S. Commensurability and Mobility in Two-Dimensional Molecular
Patterns on Graphite. Science 1991, 253, 424–427.
37) Hoeppener, S.; Chi, L.; Fuchs, H. Molecular Arrangement of Fatty Acids at the SolidLiquid Interface Visualized by Chemical Decoration. Chem. Phys. Chem. 2003, 4, 494–
498.
38) Molecular Simulations Inc., WebLab Viewer Lite version 3.20. 1998; www.msi.com.
ACS Paragon Plus Environment
30
Page 31 of 32
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
The Journal of Physical Chemistry
39) Elemans, J. A. A. W.; De Cat, I.; Xu, H.; De Feyter, S. Two-dimensional chirality at
liquid–solid interfaces. Chem. Soc. Rev. 2009, 38, 722-736.
40) Ernst, K.-H. Molecular chirality at surfaces. Phys. Status Solidi B, 2012, 249, 2057–2088
41) Piot, L.; Marchenko, A.;Wu, J.; Müllen, K.; Fichou, D. Structural Evolution of Hexaperi-hexabenzocoronene Adlayers in Heteroepitaxy on n-Pentacontane Template
Monolayers. J. Am. Chem. Soc. 2005, 127, 16245–16250.
42) Phillips, T. K.; Bhinde, T.; Clarke, S. M.; Lee, S. Y.; Mali, K. S.; De Feyter, S.
Adsorption of Aldehydes on a Graphite Substrate: Combined Thermodynamic Study of
C6–C13 Homologues with a Structural and Dynamical Study of Dodecanal. J. Phys.
Chem. C 2010, 114, 6027–6034.
43) Hoshino, A.; Isoda, S.; Kurata, H.;
Kobayashi, T. Scanning tunneling microscope
contrast of perylene-3,4,9,10-tetracarboxylic-dianhydride on graphite and its application
to the study of epitaxy. J. Appl. Phys. 1994, 76, 4113–4120.
ACS Paragon Plus Environment
31
The Journal of Physical Chemistry
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Page 32 of 32
TOC Image
ACS Paragon Plus Environment
32