Harnessing by a diacetylene unit: A molecular design for porous two-dimensional network formation at the liquid/solid interface

Article abstract of DOI:10.1039/c3cc47949h

Through the precise molecular design for alkoxy dehydro[12]annulene derivatives harnessed by a diacetylene unit in each alkyl chain, porous two-dimensional networks with giant pores were formed at the liquid/graphite interface.

Full text of DOI:10.1039/c3cc47949h

Volume 50 Number 22 18 March 2014 Pages 2807–2970
ChemComm
Chemical Communications
www.rsc.org/chemcomm
ISSN 1359-7345
COMMUNICATION
Steven De Feyter, Yoshito Tobe et al.
Harnessing by a diacetylene unit: a molecular design for porous
two-dimensional network formation at the liquid/solid interface

ChemComm
View Article Online
View Journal | View Issue
COMMUNICATION
Harnessing by a diacetylene unit: a molecular
design for porous two-dimensional network
formation at the liquid/solid interface†
Cite this: Chem. Commun., 2014,
50, 2831
Received 16th October 2013,
Accepted 2nd December 2013
Kazukuni Tahara,‡a Jinne Adisoejoso,‡b Koji Inukai,a Shengbin Lei,b Aya Noguchi,a
Bing Li,b Willem Vanderlinden,b Steven De Feyter*b and Yoshito Tobe*a
DOI: 10.1039/c3cc47949h
www.rsc.org/chemcomm
Through the precise molecular design for alkoxy dehydro[12]annulene challenge to form stable 2D porous networks with large pore sizes,
derivatives harnessed by a diacetylene unit in each alkyl chain, porous particularly at the liquid–solid interface.
two-dimensional networks with giant pores were formed at the
liquid/graphite interface.
Recently, Zimmt et al. reported that a kinked diacetylene (DA) unit
in alkyl chains linked to anthracene cores could control 2D pattern
formation via recognition of steric units that are complementary to
Surface confined two-dimensional (2D) molecular networks formed the DA units.8 We reasoned that the presence of a DA unit in the alkyl
by self-assembly of organic molecules are a subject of interest from chains of DBAs would favor the formation and stabilization of 2D
the perspective of various applications in the field of nanoscience porous networks, even for large pore sizes, by reducing the toll on
and nanotechnology.1 In particular, 2D porous molecular networks entropy that would otherwise be imposed for methylenes to adopt an
have received quite some attention due to the ability of these surface- all-anti conformation in the extended alkyl chains.9 We planned to
confined molecular networks to accommodate guest molecules in utilize this stabilizing effect of DA units to fabricate giant pores with a
the nanowells.2 In general, the formation of porous molecular diameter of over 5 nm using DBA building blocks. We noted that a
networks is thermodynamically unfavorable because of the low precise molecular design, more specifically the location of DA units, is
molecular surface density. Therefore, there are only few examples a requisite to achieve optimal van der Waals interactions between
of 2D networks with pores or nanowells with diameters larger than alkyl chains. Moreover since four DA units would be aligned parallel
5 nm.3 However, by a careful molecular design in combination in the interdigitated chains of porous networks of DBAs with DA units
with optimization of experimental conditions, such as solvent,4 (DBA-DAs), these may serve as precursors of novel 2D polymers.10
concentration5 and temperature,6 it should be possible to favor
Here we report the design and synthesis of DBA-DA12.12,
the formation of such large pores at the liquid/solid interface. DBA-DA17.17, DBA-DA24.25 and DBA-DA32.33 having DA units
We have reported the formation of porous honeycomb-type at different positions within the alkyl substituents (Fig. 1).
structures of alkoxy dehydrobenzo[12]annulenes (DBAs, Fig. 1a) at
the liquid/solid interface. The porous networks are stabilized by van
der Waals interactions between interdigitated alkyl chains of
adjacent molecules,7 and the pore size can in principle be enlarged
by elongation of the alkyl chain. However, nonporous structures
were observed for the DBAs having relatively long alkoxy chains
even at low solute concentrations.5c For instance, a DBA derivative
with –OC30H61 chains exhibited porous structures only in small
areas even under submonolayer conditions.3a Therefore, it is a real
a Division of Frontier Materials Science, Graduate School of Engineering Science,
Osaka University, Toyonaka, Osaka 560-8531, Japan.
E-mail: tobe@chem.es.osaka-u.ac.jp; Tel: +81-(0)6-6850-6225
b Division of Molecular Imaging and Photonics, Department of Chemistry,
KU Leuven, Celestijnenlaan 200 F, 3001 Leuven, Belgium.
Fig. 1 (a) Chemical structures of DBA–OCn and DBA–DAs. (b)–(e) PM3
optimized molecular models of DBA–DA12.12, DBA–DA17.17, DBA–DA24.25
and DBA–DA32.33 under vacuum. In (c)–(e) different chains are colored in
pink and blue.
E-mail: steven.defeyter@chem.kuleuven.be; Tel: +32-16-3-27921
† Electronic supplementary information (ESI) available: Experimental details,
STM images, and syntheses of DBA-DAs. See DOI: 10.1039/c3cc47949h
‡ Both authors contributed equally to this work.
This journal is ©The Royal Society of Chemistry 2014
Chem. Commun., 2014, 50, 2831--2833 | 2831

View Article Online
Communication
ChemComm
Self-assembly of the DBA-DAs was investigated at the 1,2,4-trichloro- packing and a small gap between the inner DA units in the type I
benzene (TCB)/graphite interface using scanning tunnelling structure.
microscopy (STM). DBA-DA24.25 and DBA-DA32.33 formed
To solve the mismatch in the type I structure of DBA-DA17.17, we
honeycomb structures with giant pores having a diameter of designed DBA-DA24.25 with alternating chains of different lengths,
6 and 7 nm, respectively. Moreover, DBA-DAs formed the porous while keeping the length of the alkyl chain spacer between the
structures over wider concentration ranges compared to DBAs DBA core and the diacetylene unit the same: R1 (10-DA-10) and R2
with saturated alkyl chains of comparable lengths, revealing the (10-DA-11) chains. In addition to the positive packing effects, the
enhanced stabilization effect of the DA units on the porous longer chain length should also lead to an enlarged pore size. The
network structures.
MM simulations for the type I and II structures of DBA-DA24.25
First we assume that the two alkoxy oxygen atoms attached to a predict no steric mismatch between the DA units in both cases
benzene ring orient in a synclinal arrangement rather than in the (Fig. S3a, ESI†). The type I structure was more stable than the
same direction or in an anticlinal arrangement based on a theore- type II structure by 12.7 kcal molÀ1. In the latter structure, van
tical study using the B3LYP/6-31g(d) level of theory (Fig. S1, ESI†). der Waals contacts between the alkyl chains were smaller.
Hereafter we abbreviate the alkyl chains containing the DA unit as Indeed, there is a small gap between the methyl groups at the
m-DA-n where m and n refer to the number of carbon atoms from end of alkyl chains and DBA cores.11
the oxygen atom to the DA unit and from the DA unit to the terminal
All these compounds were synthesized to test the predictions
methyl group in the chain, respectively. Then we designed of modeling. In addition, DBA-DA32.33 having two different long
the simplest compound DBA-DA12.12 having six identical chains chains R1 (14-DA-14) and R2 (14-DA-15) was designed for the
(4-DA-4 chains). Molecular modeling of a dimer of DBA-DA12.12 formation of even larger pores (Fig. S3b, ESI†). Syntheses of
predicts that the four DA units cannot align parallel (Fig. S2a, ESI†). these four DBA-DAs are described in the ESI.†
However, by changing the location of the DA unit in three of the
A TCB solution of DBA-DA12.12 (9.3 Â 10À4 M) was dropped on a
alternating alkyl chains of DBA-DA12.12 from 4-DA-4 to 3-DA-5, the graphite surface and examined by STM. However, monolayer for-
modeling shows that all four DA units in the corresponding dimer mation was not observed, probably due to the significant structural
can adopt parallel arrangement (Fig. S2b, ESI†). Based on these mismatch of the DA units as predicted by modeling. In contrast, a
results, DBA-DA17.17 comprising two different chains (R1 = 6-DA-7 structurally ordered monolayer of DBA-DA17.17 was observed at the
and R2 = 7-DA-6; chain length is identical) in an alternating fashion TCB/graphite interface. In the STM images (Fig. 3a and b), the bright
was designed. The chains were elongated to increase intermolecular features correspond to the conjugated cores of the DBA-DA mole-
and molecule–substrate interactions and enlarge the pore size. cules and the darker parts are composed of four interdigitated alkyl
Modeling predicts that DBA-DA17.17 can form two structurally chains, revealing the formation of the honeycomb lattice. The
unequivalent honeycomb structures (type I and II) which differ in observed domain size was larger than the typical scanning size
surface molecular density depending on the positions of R1 and R2 (10 000 nm2). Surprisingly, comparison of the structural parameters
within the interdigitated four alkyl chains. To evaluate the relative with those calculated by the MM simulations (Fig. 2, Table S1, ESI†)
stability of the type I and II structures, molecular mechanics revealed the formation of the type I honeycomb structure. This
simulations were performed using the hexamer models on a observation is in contrast with the relative stability predicted by the
graphite lattice, in which the peripheral alkoxy chains were replaced MM simulations indicating that in this case the network structure is
by methoxy groups (Fig. 2, see ESI†). The possibility of solvent controlled by the molecular surface density rather than the inter-
co-adsorption as a stabilizing effect was not taken into account in molecular interactions. Another possibility is a stabilization effect by
the simulations. As a result, the type II structure turned out to be co-adsorption of solvent molecules in the pore.
more stable by 10.7 kcal molÀ1 because of a non-ideal diacetylene
In DBA-DA24.25, large domains of the honeycomb structure
were observed at the TCB/graphite interface (Fig. 4a and b).
‘‘Kinks’’ due to the DA units are clearly observed in the middle
of the alkyl chains.12 Comparison of the unit cell parameters
with those predicted by the MM simulations (Fig. S3a and
Fig. 2 Optimized structures by the MM simulations (MM3 parameters) of
the hexamer models formed by DBA–DA17.17 with high (type I structure;
a = b = 5.3 nm, g = 601 and d = 0.121 molecule nmÀ2) and low (type II
structure; a = b = 5.7 nm, g = 601 and d = 0.107 molecule nmÀ2) molecular
density. Side chains R1 (7-DA-6) and R2 (6-DA-7) are colored in blue and
pink, respectively. In the type I structure, a gap and a shift between the
inner DA units is indicated by a yellow circle.
Fig. 3 STM images (a, b) and a molecular model (c) of the monolayer
formed by DBA–DA17.17 at the TCB/graphite interface. Tunneling para-
meters are Iset = 0.21 nA, Vset = À0.84 V for (a) and Iset = 0.17 nA, Vset
=
À0.79 V for (b), respectively. Unit cell parameters are a = b = 5.3 Æ 0.1 nm
and g = 61 Æ 31. The concentration of DBA–DA17.17 is 8.2 Â 10À4 M.
2832 | Chem. Commun., 2014, 50, 2831--2833
This journal is ©The Royal Society of Chemistry 2014

View Article Online
ChemComm
Communication
networks can be further stabilized. Moreover, the porous network
of DBA-DA24.25 was found to be stable enough to preserve its
structure after solvent evaporation (Fig. S7, ESI†).8
We have shown that through a precise design of DBA derivatives
having a diacetylene unit in each alkyl chain porous networks with
giant 2D pores can be stabilized at the liquid/solid interface. The
diameters of the pores reached 6 and 7 nm for DBA-DA24.25 and
DBA-DA32.33, respectively. Upon simply introducing diacetylene
units within the alkyl chains, the resultant porous hexagonal net-
works were observed to be more stable than their counterparts that
lack the diacetylene units. The present knowledge is important for
the construction of porous networks with giant pores and for 2D
crystal engineering in general. Investigation on interlinking the DA
units aiming at porous 2D polymer synthesis is currently underway.
This work was supported by the Grant-in-Aid for Scientific
Research from the Ministry of Education, Culture, Sports, Science,
and Technology, Japan (19750033, 21245012, 23111710), the Fund of
Scientific Research – Flanders (FWO), KU Leuven (GOA), and the
Belgian Federal Science Policy Office through IAP-7/05. The research
leading to these results has also received funding from the European
Research Council under the European Union’s Seventh Framework
Programme (FP7/2007-2013)/ERC Grant Agreement no. 340324.
Fig. 4 STM images (a, b) and a molecular model (c) of the monolayer
formed by DBA–DA24.25 at the TCB/graphite interface. Tunneling para-
meters are Iset = 0.1 nA, Vset = À1.0 V for (a) and Iset = 0.1 nA, Vset = À1.0 V
for (b), respectively. Unit cell parameters are a = b = 7.0 Æ 0.1 nm, and g =
60 Æ 21. The concentration of DBA–DA24.25 is 1.9 Â 10À6 M.
Table S1, ESI†) confirmed the formation of the more dense type
I honeycomb structure. The pore diameter reaches 6.0 nm (the
distance across the DA units). Also DBA-DA32.33 formed a
porous monolayer network at the TCB/graphite interface
(Fig. 5). DA units are clearly observed as bright lines in the
middle of interdigitated alkyl chains. The diameter of the pore
becomes ca. 7 nm (distance between the DA units). The typical
domain size is smaller than the other DBA-DAs though, and the
degree of order is lower. However, in contrast to the monolayer
of DBA-OC30, so lacking DA units,3a nonporous densely packed
structures were scarcely observed at low concentrations.
Notes and references
The honeycomb structures formed by DBA-DAs at the TCB/
graphite interface were observed over a wide concentration
range reflecting the stabilization effect of the DA units. Similar
to DBAs,5c DBA-DAs were shown to exhibit polymorphism between
the porous and nonporous structures depending on the solute
concentration. In order to qualitatively compare the increased
stability provided by the DA units, the observed proportion of porous
networks was probed as a function of solute concentration and
compared to DBA-OC18.5c DBA-OC18 only formed porous structures
at a concentration lower than 1.0 Â 10À6 M (Fig. S6, ESI†). In
contrast, porous structures are formed at a concentration lower than
1.9 Â 10À6 M for DBA-DA24.25 and 9.2 Â 10À7 M for DBA-DA32.33,
despite the lower molecular surface densities of the porous networks
of the DBA-DAs (0.07 and 0.05 molecule nmÀ2) with respect to DBA-
OC18 (0.10 molecule nmÀ2). In general, given the lower molecular
surface densities and larger pore sizes, at the same concentration,
the proportion of porous networks is always larger for DBA deriva-
tives with DA units in their chains. These results indicate that by
incorporating DA units within the rims of the pores, porous
1 (a) J. V. Barth, Annu. Rev. Phys. Chem., 2007, 58, 375–407; (b) J. V. Barth,
G. Costantini and K. Kern, Nature, 2005, 437, 671–679; (c) J. A. A. W.
Elemans, L. S. Lei and S. De Feyter, Angew. Chem., Int. Ed., 2009, 48,
7298–7332.
2 (a) D. Bonifazi, S. Mohnani and A. Llanes-Pallas, Chem.–Eur. J., 2009,
15, 7004–7025; (b) X. Ma, Y. Yang, K. Deng, Q. Zeng, K. Zhao,
C. Wang and C. Bai, J. Mater. Chem., 2008, 18, 2074–2081.
¨
3 (a) K. Tahara, S. Lei, D. Mossinger, H. Kozuma, K. Inukai, M. Van
¨
der Auweraer, F. C. De Schryver, S. Hoger, Y. Tobe and S. De Feyter,
Chem. Commun., 2008, 3897–3899; (b) D. Ku¨hne, F. Klappenberger,
R. Decker, U. Schlickum, H. Brune, S. Klyatskaya, M. Ruben and
J. V. Barth, J. Am. Chem. Soc., 2009, 131, 3881–3883.
4 Y. Yang and C. Wang, Curr. Opin. Colloid Interface Sci., 2009, 14, 135–147.
5 (a) L. Kampschulte, T. L. Werblowsky, R. S. K. Kishore, M. Schmittel,
W. M. Heckl and M. Lackinger, J. Am. Chem. Soc., 2008, 130, 8502–8507;
(b) C.-A. Palma, J. Bjork, M. Bonini, M. S. Dyer, A. Llanes-Pallas,
`
D. Bonifazi, M. Persson and P. Samorı, J. Am. Chem. Soc., 2009, 131,
13062–13071; (c) S. Lei, K. Tahara, F. C. De Schryver, M. Van der Auweraer,
Y. Tobe and S. De Feyter, Angew. Chem., Int. Ed., 2008, 47, 2964–2968.
6 (a) R. Gutzler, T. Sirtl, J. F. Dienstmaier, K. Mahata, W. M. Heckl,
M. Schmittel and M. Lackinger, J. Am. Chem. Soc., 2010, 132,
5084–5090; (b) A. Bellec, C. Arrigoni, G. Schull, L. Douillard,
C. Fiorini-Debuisschert, F. Mathevet, D. Kreher, A.-J. Attias and
F. Charra, J. Chem. Phys., 2011, 134, 124702; (c) M. O. Blunt,
J. Adisoejoso, K. Tahara, K. Katayama, M. Van der Auweraer,
Y. Tobe and S. De Feyter, J. Am. Chem. Soc., 2013, 135, 12068–12075.
7 (a) K. Tahara, S. Furukawa, H. Uji-i, T. Uchino, T. Ichikawa, J. Zhang,
W. Mamdouh, M. Sonoda, F. C. De Schryver, S. De Feyter and Y. Tobe,
J. Am. Chem. Soc., 2006, 128, 16613–16625; (b) K. Tahara, S. Lei,
J. Adisoejoso, S. De Feyter and Y. Tobe, Chem. Commun., 2010, 46,
8507–8525.
8 Y. Xue and M. B. Zimmt, Chem. Commun., 2011, 47, 8832–8834.
9 E. L. Eliel and S. H. Wilen, Stereochemistry of organic compounds,
Jhon Wiley & Sons, New York, 1994, pp. 601–604.
10 (a) J. Sakamoto, J. van Heijst, O. Lukin and A. D. Schlu¨ter, Angew.
Chem., Int. Ed., 2009, 48, 1030–1069; (b) J. W. Colson and W. R. Dichtel,
Nat. Chem., 2013, 5, 453–465.
11 E. Ghijsens, O. Ivasenko, K. Tahara, H. Yamaga, S. Itano,
T. Balandina, Y. Tobe and S. De Feyter, ACS Nano, 2013, 7, 8031–8042.
12 In other solvents such as 1-phenyloctane, tetradecane, and 1-
octanoic acid, DBA-DA24.25 formed non-porous structures. Such
solvent effect was reported previously. See ref. 7.
Fig. 5 STM images (a, b) of the monolayer formed by DBA–DA32.33 at
the TCB/graphite interface. Tunneling parameters are Iset = 0.1 nA, Vset
=
À0.70 V for (a) and Iset = 0.1 nA, Vset = À0.70 V for (b), respectively. The
concentration of DBA–DA32.33 is 9.2 Â 10À7 M.
This journal is ©The Royal Society of Chemistry 2014
Chem. Commun., 2014, 50, 2831--2833 | 2833