cis/trans Isomerization of Azobenzene Dimers
FULL PAPER
128.96, 123,55, 122.94, 120.77, 120.58, 41.58, 21.23 ppm. HRMS
(m/z): calcd. for C27H24N4: 404.2000; found 404.2034.
mechanism does not appear to have been changed signifi-
cantly by the ring strain.
Acknowledgments
Conclusion
We thank TACC (Tsukuba Advanced Computing Center) for pro-
viding the calculation facilities. Y.N. thanks NEDO (New Energy
and Industrial Technology Development Organization) for a post-
doctoral fellowship.
The effect of a cyclic structure on the photochemical
isomerization of azobenzene dimers can be explained in
terms of absorption spectra change and the molecular mo-
tion in the excited states. A multidimensional potential en-
ergy surface should be considered for elucidation of the re-
action mechanism. The ring strain in the macrocyclic azo-
benzene dimer increases the activation energy and acti-
vation entropy for the thermal (Z) Ǟ (E) isomerization of
the azobenzene moiety. This knowledge of the correlation
between structure and reactivity of azobenzene gives signifi-
cant information for controlling the isomerization to estab-
lish photoresponsive functional materials that utilize the
isomerization of azobenzene.
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Experimental Section
General: 1H NMR spectra were recorded on JEOL GSX-270
(270 MHz), Varian Gemini-2000/300BB (300 MHz), or JEOL
LA600 (600 MHz) instruments. 13C NMR spectra were recorded
on a Varian Gemini-2000/300BB (75 MHz) machine. UV/Vis ab-
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trophotometer. Ratios of the isomers were examined by RP-HPLC
(ODS-80Ts, TOSO Co./methanol). Photoirradiation was carried
out with a 150-W xenon lamp fitted with a monochromator with a
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corresponding crystal structure were used as the input geometries
for (E,E)-1, (E,Z)-1, and (Z,Z)-1. Flat molecular geometries, with
all benzene rings on the same plane, were applied for the input
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Synthesis of (E,E)-Bis[3-(3-tolylazo)phenyl]methane (2): 3-Ni-
trosotoluene (411 mg, 3.4 mmol) and bis(3-aminophenyl)methane
(347 mg, 1.8 mmol) were dissolved in acetic acid (20 mL) and the
system was stirred at room temperature for 18 hours. After addition
of saturated Na2CO3 solution (10 mL) the reaction mixture was
extracted with ethyl acetate. The organic layer was washed with
brine and dried with MgSO4, and the solvent was evaporated under
reduced pressure. Repeated chromatography on silica gel (column
1.5×25 cm, hexane/AcOEt, 19:1) gave the bis-azo compound
(87.9 mg, 13%%) as an orange oil in high purity as judged by
HPLC and 1H NMR spectroscopic data. Rf = 0.27 (hexane/AcOEt,
1
19:1). H NMR (300 MHz, CDCl3): δ = 7.84–7.74 (m, 8 H), 7.47–
7.31 (m, 8 H), 4.21 (s, 2 H), 2.46 (s, 6 H) ppm. 13C NMR (75 MHz,
CDCl3): δ = 153.06, 152.85, 141.85, 139.06, 131.86, 131,60, 129.35,
Eur. J. Org. Chem. 2006, 1296–1302
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