to the metal substrate over an intervening distance of 30 cm in ultra-
high vacuum (1 Â 10À8 Pa), followed by characterization using STM
(JEOL Ltd., SPM-4500X) at 150 K using an electrochemically etched
tungsten tip. The tunneling current, It, and voltage, Vs, were 80–100 pA
and +1.0 V, respectively, and are noted in the respective figure
captions.
groups (either clockwise or anticlockwise) in response to the
substrate.13 However, a phase boundary was not observed
probably because it is precluded by the enantiomerism of the
non-identical assemblies.
In summary, we have observed new conformations of phenyl
groups in tetraphenylporphyrin and their effect on the packing
of the supramolecular structure of the TDtBHPP molecules.
Furthermore, spontaneous formation of a mixed conformer of
TDtBHPP has been obtained. Now, TDtBHPP molecules have
been shown to form not only interlocked 2D lattice interfaces11
but also an arrangement where the difference between the
lattices of two 2D crystal structures is compensated for by the
existence of an unsymmetrical molecular conformation. Our
current motivation for studying such a phenomenon lies in the
possibility that, with the knowledge gained from its analysis we
may ‘engineer’ similar features into molecular species for
adsorption. Ultimately, this may result in perfectly crystalline
heterogeneous molecular monolayers whose structure and phy-
sical properties should be of substantial interest.
1 (a) C. Joachim, J. K. Gimzewski and A. Aviram, Nature, 2000, 408,
541–548; (b) J. K. Gimzewski and C. Joachim, Science, 1999, 283,
1683–1688.
2 (a) J. A. Theobald, N. S. Oxtoby, M. A. Phillips, N. R. Champness
and P. H. Beton, Nature, 2003, 424, 1029; (b) P. Samori,
A. Fechtenkotter, F. Jackel, T. Bohme, K. Mullen and J. Rabe,
¨
¨
¨
J. Am. Chem. Soc., 2001, 123, 11462.
¨
3 Z. Liu, A. M. Yasseri, J. S. Lindsey and D. F. Bocian, Science, 2003,
302, 1543–1545.
4 K. M. Kadish, G. Royal and E. van Caemelbecke, in The Porphy-
rin Handbook, ed. K. M. Kadish, K. M. Smith and R. Guilard, 1999,
Academic Press, vol. 8.
5 T. Yokoyama, S. Yokoyama, T. Kamikado, Y. Okuno and S.
Mashiko, Nature, 2001, 413, 619.
6 F. Moresco, G. Meyer, K.-H. Rieder, H. Tang, A. Gourdon and C.
Joachim, Surf. Sci., 2002, 499, 94–102.
7 T. A. Jung, R. R. Schittler and J. K. Gimzewski, Nature, 1997, 386,
696–698.
8 (a) F. C. Frank and J. H. van der Merwe, Proc. R. Soc. London, Ser.
A, 1949, 198, 216; (b) J. H. van der Merwe, in Single Crystal Films,
ed. M. H. Francombe and H. Sato, Pergamon, New York, 1964,
p. 139.
9 (a) K. Mistry, M. Armstrong, C. Auth, S. Cea, T. Coan, T. Ghani,
T. Hoffmann, A. Murthy, J. Sandford, R. Shaheed, K. Zawadzki,
K. Zhang, S. Thompson and M. Bohr, Symp. VLSI Tech. Dig.,
2004, 50–51; (b) M. L. Lee and E. A. Fitzgerald, J. Appl. Phys.,
2003, 94, 2590–2596.
Acknowledgements
The authors are grateful for support received from the Special
Coordination Funds for Promoting Science and Technology
from MEXT, Japan through an ICYS Fellowship (J. P. H.).
10 For one significant example of discotics substituted with a variety of
functional groups and assembled at surfaces see S. Ito, M. Wehme-
References
w 5,10,15,20-Tetrakis(3,5-di-t-butyl-4-hydroxyphenyl)porphyrin
was
ier, J. D. Brand, C. Kubel, R. Epsch, J. P. Rabe and K. Mullen,
¨
Chem.–Eur. J., 2000, 6, 4329.
¨
prepared as previously reported using the Adler modification of the
Rothemund synthesis whereby pyrrole was condensed with 3,5-di-t-
butyl-4-hydroxybenzaldehyde in refluxing propionic acid.14 After cool-
ing, the resulting porphyrinic precipitate was filtered then purified by
column chromatography followed by recrystallization from dichloro-
methane/methanol. The purple microcrystalline solid was dried in vacuo
before use in STM experiments. Atomically clean single crystals of
Cu(111) used as substrates were prepared by Ar+ sputtering and
annealing (700 K) cycles. Sub-monolayer coverage of the substrate
was obtained by sublimation for 10 min at 320 1C from a Knudsen cell
11 J. P. Hill, Y. Wakayama, W. Schmitt, T. Tsuruoka, T. Nakanishi,
M. L. Zandler, A. L. McCarty, F. D’Souza, L. R. Milgrom and K.
Ariga, Chem. Commun., 2006, 2330–2332.
12 T. Yokoyama, S. Yokoyama, T. Kamikado and S. Mashiko,
J. Chem. Phys., 2001, 115, 3814–3818.
13 T. Sekiguchi, Y. Wakayama, S. Yokoyama, T. Kamikado and
S. Mashiko, Thin Solid Films, 2004, 464/465, 393–397.
14 A. D. Adler, F. R. Longo, J. D. Finarelli, J. Goldmacher, J. Assour
and L. Korsakoff, J. Org. Chem., 1967, 32, 476.
This journal is ꢀc the Owner Societies 2006
Phys. Chem. Chem. Phys., 2006, 8, 5034–5037 | 5037