The Journal of Physical Chemistry B
ARTICLE
In most of this work, experiment and theory are in good
agreement regarding the spectroscopic, electronic, and thermo-
dynamic data. The theorically found additivity of fragment UV/
spectra for compounds 3 and 4, and nonadditivity for 1 and 2, is a
direct proof of the decoupling of fragment π-systems in the
former species, a prerequisite for restoring the switching ability.
Moreover, calculations provide mechanistic insight, indicating a
preferred pathway for the thermal back Z,Z f Z,E f E,E
isomerization via inversion on the inner N-atoms.
The above-described strategy for achieving almost quantita-
tive photoswitching of para-connected azobenzenes can be used
to build complex photoresponsive systems.6,7 For instance,
connecting several electronically and geometrically decoupled
azobenzenes in their para-position results in linear rigid rod
oligomers and polymers, displaying significant changes in size
and shape upon UV irradiation.12 Integration of such shrinkable
rigid rod architectures into self-assembled nanostructured soft
materials to design systems, capable of efficiently converting light
into molecular and eventually macroscopic motion, is currently
being explored in our laboratories.
(b) Kausar, A.; Nagano, H.; Ogata, T.; Nonaka, T.; Kurihara, S. Angew.
Chem., Int. Ed. 2009, 48, 2144–2147. For a general overview on surface
relief gratings, see: (c) Smart Light-Responsive Materials: Azobenzene-
Containing Polymers and Liquid-Crystals; Zhao, Y., Ikeda, T., Eds.; John
Wiley and Sons: Hoboken, NJ, 2009; Chapter 11.
(6) Russew, M. M.; Hecht, S. Adv. Mater. 2010, 22, 3348–3360 and
references therein.
(7) For comprehensive reviews on azobenzene photochromes, see:
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(b) Organic Photochromes; El’tsov, A. V., Ed.; Consultants Bureau: New
York, 1990; Chapter 3. (c) Photochromism: Molecules and Systems; D€urr,
H., Bouas-Laurent, H., Eds.; Elsevier: Amsterdam, 2003; Chapter 4.
(8) For selected examples, see: (a) Yu, Y. L.; Nakano, M.; Ikeda, T.
Nature 2003, 425, 145. (b) Hosono, N.; Kajitani, T.; Fukushima, T.; Ito,
K.; Sasaki, S.; Takata, M.; Aida, T. Science 2010, 330, 808–811. For a
general overview, see: (c) Smart Light-Responsive Materials: Azobenzene-
Containing Polymers and Liquid-Crystals; Zhao, Y., Ikeda, T., Eds.; John
Wiley and Sons: Hoboken, NJ, 2009; Chapter 3.
(9) Koshima, H.; Ojima, N.; Uchimoto, H. J. Am. Chem. Soc. 2009,
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(10) For a comprehensive review on diarylethenes, see: Irie, M.
Chem. Rev. 2000, 100, 1685–1716.
(11) For a representative example, see: Kobatake, S.; Takami, S.;
Muto, H.; Ishikawa, T.; Irie, M. Nature 2007, 446, 778–781.
(12) To be published elsewhere.
’ ASSOCIATED CONTENT
(13) (a) Cisnetti, F.; Ballardini, R.; Credi, A.; Gandolfi, M. T.;
Masiero, S.; Negri, F.; Pieraccini, S.; Spada, G. P. Chem.—Eur. J. 2004,
10, 2011–2021. (b) Peters, M. PhD Thesis; Humboldt-Universit€at zu
Berlin: Berlin, 2008.
(14) This strategy has already been reported for modulating the
absorption spectra of para-connected bisazobenzene derivatives; how-
ever, their isomerization ability has not been investigated, see: Morris,
R. J.; Brode, W. R. J. Am. Chem. Soc. 1948, 70, 2485–2488.
(15) The tert-Bu groups were placed at different positions in
compound 1 when compared to compounds 2ꢀ4 as in yet unpublished
work, the 2D self-assembly and photoswitching behavior of compound 1
at metallic surfaces was investigated (see also ref 4e).
S
Supporting Information. Synthetic details and com-
b
pound characterization, photochemistry, electrochemistry, spec-
troscopy, kinetic analyses, and computational methods. This
material is available free of charge via the Internet at http://
pubs.acs.org.
’ AUTHOR INFORMATION
Corresponding Author
*E-mail: sh@chemie.hu-berlin.de; petsaal@rz.uni-potsdam.de.
(16) For studies on the conductance of single-biphenyl junctions, see:
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’ ACKNOWLEDGMENT
Generous support by the German Research Foundation
(DFG via SFB 658, subprojects B8 and C2) is gratefully
acknowledged. Wacker Chemie AG, BASF AG, Bayer Industry
Services, and Sasol Germany are thanked for generous donations
of chemicals.
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dx.doi.org/10.1021/jp2044114 |J. Phys. Chem. B 2011, 115, 9930–9940