Azobenzene Photoisomerization
merize. When the 4-hydroxy group in AzoAMP-4 is con-
verted into an ester group, however, photoactivity is re-
stored. Since the lone pairs of electrons on the oxygen atom
are engaged in resonance with the ester carbonyl group in
AzoAMP-6, their contributions to the AB electronic struc-
ture is significantly mollified.
[1]
[2]
[3]
G. S. Hartley, Nature 1937, 140, 281.
P. Bortolus, S. Monti, J. Phys. Chem. 1979, 83, 648–652.
T. Fujino, S. Y. Arzhantsev, T. Tahara, J. Phys. Chem. A 2001,
105, 8123–8129.
T. Fujino, S. Y. Arzhantsev, T. Tahara, Bull. Chem. Soc. Jpn.
2002, 75, 1031–1040.
H. M. D. Bandara, T. R. Friss, M. M. Enriquez, W. Isley, C.
Incarvito, H. A. Frank, J. Gascon, S. C. Burdette, J. Org.
Chem. 2010, 75, 4817–4827.
[4]
[5]
Conclusions
[6]
[7]
F. Puntoriero, P. Ceroni, V. Balzani, G. Bergamini, F. Voegtle,
J. Am. Chem. Soc. 2007, 129, 10714–10719.
The current experiments suggest that removing lone pairs
from the π-system of AB containing electron-donating
groups attenuates the isomerization behavior. We showed
that this electronic effect leads to differences in the location
of conical intersections between S1 and S0. Whereas in
AzoAMP-6 conical intersection occurs closer to the transi-
tion state, in AzoAMP-6 it occurs much earlier in the inso-
merization path, leading to a frustrated isomerization. Fi-
nally, alternatives to esterification including metal-binding
are being explored in our laboratory as secondary switches
for the AB isomerization.
V. Ferri, M. Elbing, G. Pace, M. D. Dickey, M. Zharnikov, P.
Samori, M. Mayor, M. A. Rampi, Angew. Chem. 2008, 120,
3455; Angew. Chem. Int. Ed. 2008, 47, 3407–3409.
M. R. Banghart, A. Mourot, D. L. Fortin, J. Z. Yao, R. H.
Kramer, D. Trauner, Angew. Chem. 2009, 121, 9261; Angew.
Chem. Int. Ed. 2009, 48, 9097–9101.
T. Muraoka, K. Kinbara, T. Aida, Nature 2006, 440, 512–515.
E. Evangelio, J. Saiz-Poseu, D. Maspoch, K. Wurst, F. Busque,
D. Ruiz-Molina, Eur. J. Inorg. Chem. 2008, 2278–2285.
C. L. Forber, E. C. Kelusky, N. J. Bunce, M. C. Zerner, J. Am.
Chem. Soc. 1985, 107, 5884–5890.
[8]
[9]
[10]
[11]
[12]
A. A. Blevins, G. J. Blanchard, J. Phys. Chem. B 2004, 108,
4962–4968.
[13] E. Sawicki, J. Org. Chem. 1957, 22, 743–745.
[14] G. Gabor, Y. F. Frei, E. Fischer, J. Phys. Chem. 1968, 72, 3266–
3272.
Experimental Section
Computational Details: Ground and excited states were obtained by
using density functional theory (DFT) and time-dependent DFT
with the hybrid functional B3LYP and the split-valence double-zeta
basis set 6-31g**. We tested the theory to reproduce the known
conical intersections of azobenzene, the transition state, and the
(Z)-(E) energy difference, in agreement with wavefunction-based
methods such as CASSCF.[21] Our previous DFT results on azo-
benzene[5] reproduced the conical intersection between the ground
state S0 and the first excited state S1 near the midpoint of the rota-
tional pathway and the existence of an isomerization path from S2
along a concerted inversion pathway, both results in agreement
with CASSCF calculations.[16,21,22] The quantum chemistry pack-
age Gaussian 09[23] was used for all calculations. Electronic excited
states were computed at the ground-state geometry. All ground-
state geometries were obtained by relaxed scans (i.e. full geometry
optimization for all coordinates except for the constraints). For
each set of constrained angles we considered possible rotamers in-
volving the pyridine rings in 4 and 6. The lowest-energy rotamer
was considered for the computation of the potential energy surface
at each point.
[15] C. R. Crecca, A. E. Roitberg, J. Phys. Chem. A 2006, 110,
8188–8203.
[16] E. W.-G. Diau, J. Phys. Chem. A 2004, 108, 950–956.
[17] J. Yoshino, N. Kano, T. Kawashima, Chem. Commun. 2007,
559–561.
[18] C. A. Craig, R. J. Watts, Inorg. Chem. 1989, 28, 309–313.
[19] W. R. Brode, J. H. Gould, G. M. Wyman, J. Am. Chem. Soc.
1952, 74, 4641–4646.
[20] N. Siampiringue, G. Guyot, S. Monti, P. Bortolus, J. Pho-
tochem. 1987, 37, 185–188.
[21] L. Wang, W. Xu, C. Yi, X. Wang, J. Mol. Graphics Modell.
2009, 27, 792–796.
[22] A. Cembran, F. Bernardi, M. Garavelli, L. Gagliardi, G. Or-
landi, J. Am. Chem. Soc. 2004, 126, 3234–3243.
[23] M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria,
M. A. Robb, J. R. Cheeseman, G. Scalmani, V. Barone, B.
Mennucci, G. A. Petersson, H. Nakatsuji, M. Caricato, X. Li,
H. P. Hratchian, A. F. Izmaylov, J. Bloino, G. Zheng, J. L. Son-
nenberg, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hase-
gawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai,
T. Vreven, J. A. Montgomery Jr., J. E. Peralta, F. Ogliaro, M.
Bearpark, J. J. Heyd, E. Brothers, K. N. Kudin, V. N. Starov-
erov, R. Kobayashi, J. Normand, K. Raghavachari, A. Rendell,
J. C. Burant, S. S. Iyengar, J. Tomasi, M. Cossi, N. Rega, J. M.
Millam, M. Klene, J. E. Knox, J. B. Cross, V. Bakken, C. Ad-
amo, J. Jaramillo, R. Gomperts, R. E. Stratmann, O. Yazyev,
A. J. Austin, R. Cammi, C. Pomelli, J. W. Ochterski, R. L. Mar-
tin, K. Morokuma, V. G. Zakrzewski, G. A. Voth, P. Salvador,
J. J. Dannenberg, S. Dapprich, A. D. Daniels, Ö. Farkas, J. B.
Foresman, J. V. Ortiz, J. Cioslowski, D. J. Fox, Gaussian 09, Re-
vision A.1, Gaussian, Inc., Wallingford, CT, 2009.
Received: February 18, 2011
Supporting Information (see footnote on the first page of this arti-
cle): Experimental procedures, additional spectroscopic data, 1H
and 13C NMR spectroscopic data for all new compounds.
Acknowledgments
J. A. G. acknowledges support from the University of Connecticut,
the Camille and Henry Dreyfus Foundation and the National Sci-
ence Fountation for a CAREER Award (CHE-0847340).
Published Online: April 18, 2011
Eur. J. Org. Chem. 2011, 2916–2919
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
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