Rodriguez-Molina et al.
JOCArticle
FIGURE 1. (a) Line formula of a molecular compass with a polar pyridine rotator as a representative of other nitrogen heteroaromatics and
(b) representation of a crystalline array of molecular compasses and the suggested analogy to (c) an array of macroscopic compasses.
solid-state.4-6 In that context, our group has been interested in
exploring the properties of crystals made up of molecular rotors7
intended to emulate the structures and function of macroscopic
compasses and gyroscopes (Figure 1).4,8
been suggested that optimal structures of dipolar arrays
formed by the introduction of polar substituents on the
rotator will provide opportunities for a new class of materials
based on physical properties that change with the orientation
of reorienting dipoles as a function of internal and external
fields.4,5a,13,14 Among the structural features expected to
influence the dynamic and electric behavior of such materials
are their barriers to rotation, the magnitude of their dipole
moments, as well as their distances, relative orientations, and
lattice symmetries.13 Other things being equal, smaller rota-
tors are expected to have fewer steric interactions and lower
rotational barriers and greater dipoles are expected to have
stronger interactions with neighboring dipoles and external
fields.
We previously reported a set of molecular compasses with
monosusbtituted phenylene rotators having fluoro (1b),
amino (1c), cyano (1d), and nitro (1e) substituents
(Scheme 1).9,15,16 Compounds 1b-e have calculated dipole
moments between 1.49 and 4.74 D and molecular volumes
that increase modestly by ca. 0.96 to 4.1% as compared to
that of 1a.17 In spite of their reduced molecular symmetries,
these compounds were shown to have molecular and packing
structures analogous to those of the parent hydrocarbon 1a.
Crystals were obtained in a solvent-free environment grown
from CH2Cl2 and in a solvent chlathrate in the presence of
benzene, both in the triclinic space group P-1.9,15 A third
packing structure in the monoclic space group P21/c was
obtained with compound 1d from a mixture of hexane and
EtOAc.15 The two types of triclinic crystals were character-
ized by having only one molecule per unit cell with the polar
With structures consisting of substituted phenylene rota-
tors linked by triple bonds to bulky triarylmethanes, we have
described the formation of crystals that support an internal
rotation consisting of a site exchange between energy minima
related by angular displacements of 180°.4,9 With structural
elements that are relatively static linked to others that are
highly mobile, we suggested the term amphidynamic crystals
to highlight the dynamic properties of these materials.4
Using metal organic frameworks10 and molecular crystals
with nonpolar rotators, we have shown that variations in the
size and topology of the stator11 and on the size and rota-
tional symmetry order of the stator12 have a deep influence
on their internal dynamics in the solid state. However, it has
(5) (a) Akutagawa, T.; Koshinaka, H.; Sato, D.; Takeda, S.; Noro, S.-I.;
Takahashi, H.; Kumai, R.; Tokura, Y.; Nakamura, T. Nature Mater. 2009, 8,
342. (b) Trolliet, C.; Poulet, G.; Tuel, A.; Wuest, J. D.; Sautet, P. J. Am.
Chem. Soc. 2007, 129, 3621. (c) Horike, S.; Matsuda, R.; Tanaka, D.;
Matsubara, S.; Mizuno, M.; Endo, K.; Kitagawa, S. Angew. Chem., Int.
Ed. 2006, 43, 7226. (d) Sato, D.; Akutagawa, T.; Takeda, S.; Noro, S.;
Nakamura, T. Inorg. Chem. 2007, 46, 363. (e) Sato, N.; Nishikiori, S.I. Dalton
Trans. 2007, 1115. (f) Zhou, W.; Yildirim, T. Phys. Rev. B 2006, 74, 180301.
(6) Sokolov, A. N.; Swenson, D. C.; MacGillivray, L. R. Proc. Nat. Acad.
Sci. U.S.A. 2008, 105, 1794.
(7) Adopting the nomenclature suggested in ref 1e, we will use the term
molecular rotor to refer to the entire molecule, in this case as a synonym of the
term “molecular compass”. A molecular rotor itself is an assembly that
consists of a stator and rotator that are linked by an axle.
(8) For an overview of molecular structures that emulate certain aspects
of macroscopic gyroscopes, see: Skopek, K.; Hershberger, M. C.; Gladysz,
J. A. Coord. Chem. Rev. 2007, 251, 1723.
(9) (a) Dominguez, Z.; Dang, H.; Strouse, M. J.; Garcia-Garibay, M. A.
J. Am. Chem. Soc. 2002, 124, 2398. (b) Godinez, C. E.; Zepeda, G.; Garcia-
Garibay, M. A. J. Am. Chem. Soc. 2002, 124, 4701.
(10) Gould, S. L.; Tranchemontagne, D.; Yaghi, O. M.; Garcia-Garibay,
M. A. J. Am. Chem. Soc. 2008, 130, 3246.
(11) (a) Khuong, T.A.V.; Zepeda, G.; Ruiz, R.; Kahn, S. I.; Garcia-
Garibay, M.A. Cryst. Growth Des. 2004, 4, 15. (b) Godinez, C. E.; Zepeda,
G.; Mortko, C. J.; Dang, H.; Garcia-Garibay, M. A. J. Org. Chem. 2004, 69,
1652. (c) Karlen, S. D.; Godinez, C. E.; Garcia-Garibay, M. A. Org. Lett.
2006, 8 3417. (d) Karlen, S. D.; Khan, S. I.; Garcia-Garibay, M. A. Mol.
Cryst. Liq. Cryst. 2006, 456, 221. (e) Khuong, T.-A. V.; Dang, H.; Jarowski,
P. D.; Emily, F.; Maverick; Garcia-Garibay, M. A. J. Am. Chem. Soc. 2007,
129, 839. (f) Jarowski, P.D.; Houk, K. N.; Garcia-Garibay, M.A. J. Am.
(13) (a) Michl, J.; Sykes, C.H. ACS Nano 2009, 3, 1042. (b) Horinek, D.;
Michl, J. J. Am. Chem. Soc. 2003, 125, 11900. (c) de Jonge, J.J.; Ratner, M.A.;
de Leeuw, S.W. J. Phys. Chem. C 2007, 111, 3770.
(14) (a) Salech, B. E. A; Teich, M. C Fundamentals of Photonics; Wiley-
Interscience: New York, 1991. (b) Weber, M. J. Handbook of Optical Materials;
CRC Press: Boca Raton, 2002. (c) Setian, L. Applications in Electrooptics;
Prentice Hall: New York, 2001.
(15) Dominguez, Z.; Khuong, T. A. V.; Sanrame, C. N.; Dang, H.;
~
Nunez, J. E.; Garcia-Garibay, M. A. J. Am. Chem. Soc. 2003, 125, 8827.
(16) Compounds with 2,3-diamino and 2-nitro-5-amino substituents
were also reported in ref 15.
(17) The volume and dipole moment values calculated in this study for
structures minimized with the AM1 method using the program Spartan are as
follows: 1a, 606 A3 and 0 D; 1b, 611.8 A3 and 1.49 D; 1c, 618.4 A3 and 1.47 D;
1d, 625.6 A3 and 3.02 D, 1e, 630.9 A3 and 4.74 D; 1f, 617.2 A3 and 2.37 D; 2,
602.8 A3 and 1.81 D; 3, 599.2 A3 and 3.28 D; 2O, 611.5 A3 and 3.78 D; 3O,
607.8 A3 and 4.35 D.
~
Chem. Soc. 2007, 129, 3110. (g) Nunez, J. E.; Natarajan, A.; Khan, S. I.;
Garcia-Garibay, M. A. Org. Lett. 2007, 9, 3559. (h) Gould, S. L.; Rodriguez,
R. B.; Garcia-Garibay, M A. Tetrahedron 2008, 64, 8336.
(12) Karlen, S. D.; Ortiz, R; Chapman, O. L.; Garcia-Garibay, M. A.
J. Am. Chem. Soc. 2005, 127, 6554.
J. Org. Chem. Vol. 74, No. 22, 2009 8555