Organic Letters
Letter
aromatic protons, which were recovered to the initial 1H NMR
spectra in the neutral state by the neutralization with Et3N (see
nonsubstituted parent azulene could not be recovered,
presumably due to competitive oxidation or decomposition of
the protonated azulene species that lack stabilization. The color
change shown in Figure 4 also indicated that increase of the
number of fused-benzene rings significantly changed the
absorption spectra, and makes PhenAz 2 and AnthAz 3 suitable
for novel molecular probes for the detection of even weak acid
and base by the naked eye.
In conclusion, this study describes facile protocols for the
incorporation of azulene rings into PAHs, which affected their
photophysical properties. These novel azulene conjugates
possessed narrow bandgaps, excellent photooxidative resistance,
and good solubility. Blue and green colors in the neutral state
derived from absorption in the visible region, as well as unique
reversible stimuli-responsiveness, even with a weak acid and base,
are rare for pure hydrocarbons without any heteroatoms. These
results suggest that azulene-embedded PAHs are promising
candidates for novel organic electronic materials. The application
of resulting azulene conjugates to OFETs, etc., is ongoing in our
laboratory.
Kubozono, Y.; Fujiwara, A.; Yamaji, M. J. Am. Chem. Soc. 2008, 130,
10470. For indeno[1,2-b]fluorenes, see: (d) Chase, D. T.; Fix, A. G.;
Kang, S. J.; Rose, B. D.; Weber, C. D.; Zhong, Y.; Zakharov, L. N.;
Lonergan, M. C.; Nuckolls, C.; Haley, M. M. J. Am. Chem. Soc. 2012,
134, 10349.
(3) (a) Alberico, D.; Scott, M. E.; Lautens, M. Chem. Rev. 2007, 107,
174. (b) Jin, T.; Zhao, J.; Asao, N.; Yamamoto, Y. Chem. - Eur. J. 2014,
20, 3554.
(4) (a) Qian, G.; Wang, Z. Y. Chem. - Asian J. 2010, 5, 1006. (b) Weil,
T.; Vosch, T.; Hofkens, J.; Peneva, K.; Mullen, K. Angew. Chem., Int. Ed.
̈
2010, 49, 9068.
(5) (a) Maliakal, A.; Raghavachari, K.; Katz, H.; Chandross, E.; Siegrist,
T. Chem. Mater. 2004, 16, 4980. (b) Kaur, I.; Jia, W.; Kopreski, R. P.;
Selvarasah, S.; Dokmeci, M. R.; Pramanik, C.; McGruer, N. E.; Miller, G.
P. J. Am. Chem. Soc. 2008, 130, 16274.
(6) Liu, J.; Walker, B.; Tamayo, A.; Zhang, Y.; Nguyen, T.-Q. Adv.
Funct. Mater. 2013, 23, 47.
(7) (a) Zhu, X.; Tsuji, H.; Navarrete, J. T. L.; Casado, J.; Nakamura, E.
J. Am. Chem. Soc. 2012, 134, 19254. (b) Murai, M.; Maekawa, H.;
Hamao, S.; Kubozono, Y.; Roy, D.; Takai, K. Org. Lett. 2015, 17, 708.
(8) (a) Gordon, M. Chem. Rev. 1952, 50, 127. (b) Hafner, K. Angew.
Chem. 1958, 70, 419. (c) Nozoe, T. Pure Appl. Chem. 1971, 28, 239.
(d) Xin, H.; Gao, X. ChemPlusChem 2017, 82, 945. For recent works,
see: (e) Murai, M.; Iba, S.; Takai, K. Jpn. Kokai Tokkyo Koho, JP
2015172009 A 20151001, 2015. (f) Yang, X.; Shi, X.; Aratani, N.;
Gonca̧ lves, T. P.; Huang, K.-W.; Yamada, H.; Chi, C.; Miao, Q. Chem.
Sci. 2016, 7, 6176.
ASSOCIATED CONTENT
* Supporting Information
■
(9) (a) Kurotobi, K.; Miyauchi, M.; Takakura, K.; Murafuji, T.;
Sugihara, Y. Eur. J. Org. Chem. 2003, 2003, 3663. For iridium-catalyzed
silylation of azulene, see: (b) Murai, M.; Takami, K.; Takai, K. Org. Lett.
2015, 17, 1798. For palladium-catalyzed arylation, see: (c) Murai, M.;
Yanagawa, M.; Nakamura, M.; Takai, K. Asian J. Org. Chem. 2016, 5, 629.
(10) Murai, M.; Hosokawa, N.; Roy, D.; Takai, K. Org. Lett. 2014, 16,
4134.
(11) Although the synthesis of naphth[2,1-a]azulenes having
substituents have been reported, there is no study on the relationship
between the chemical structures and physical properties. See: Yasunami,
M.; Yang, P. W.; Kondo, Y.; Noro, Y.; Takase, K. Chem. Lett. 1980, 9,
167.
S
The Supporting Information is available free of charge on the
Experimental procedures, spectroscopic data for all new
compounds, 1H and 13C NMR spectra, and DFT
calculation details (PDF)
X-ray data of compound 1 (CIF)
AUTHOR INFORMATION
Corresponding Authors
■
(12) (a) Plattner, P. A.; St. Pfau, A. Helv. Chim. Acta 1937, 20, 224.
(b) Michl, J.; Thulstrup, E. W. Tetrahedron 1976, 32, 205. (c) Fabian, J.;
Zahradník, R. Angew. Chem., Int. Ed. Engl. 1989, 28, 677.
ORCID
(13) Clar, E. The Aromatic Sextet; Wiley: London, 1972.
(14) Because UV−vis absorption change occurred in a single step even
with excess TFA, monocation might be the plausible species rather than
dication, which was generated in the reaction with TFA. Since ESR
spectrum of the powder and solution sample showed no signal,
generation of azulenium cation species, which is proposed in the
following previous reports, can be ruled out. (a) Wang, F.; Lai, Y.-H.;
Kocherginsky, N. M.; Kosteski, Y. Y. Org. Lett. 2003, 5, 995. (b) Wang,
X.; Ng, J.-K.; Jia, P.; Lin, T.; Cho, C. M.; Xu, J.; Lu, X.; He, C.
Macromolecules 2009, 42, 5534.
(15) Azulenes are known to have photophysical properties that are
significantly sensitive to pH change. Protonation is reported to occur at
the 1- and 3-positions of azulene ring, which resulted in the appearance
of the new absorption in the visible and NIR regions derived from its
azulenium cation. For recent examples, see: (a) Murai, M.; Amir, E.;
Amir, R. J.; Hawker, C. J. Chem. Sci. 2012, 3, 2721. (b) Murai, M.; Ku, S.-
Y.; Treat, N. D.; Robb, M. J.; Chabinyc, M. L.; Hawker, C. J. Chem. Sci.
2014, 5, 3753. (c) Amir, E.; Murai, M.; Amir, R. J.; Cowart, J. S., Jr;
Chabinyc, M. L.; Hawker, C. J. Chem. Sci. 2014, 5, 4483. (d) Tang, T.;
Lin, T.; Wang, F.; He, C. J. Phys. Chem. B 2015, 119, 8176.
spectra of NaphAz 1 and PhenAz 2 upon the protonation by TFA.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was financially supported by a Grant-in-Aid for
Scientific Research (C) (No. 16K05778) from MEXT, Japan,
and the Advanced Catalytic Transformation program for Carbon
utilization (ACT-C) project of the Japan Science and
Technology Agency. M.M. thanks ADEKA Award in Synthetic
Organic Chemistry, Japan, and Sumitomo Foundation. We
gratefully thank Dr. Sobi Asako, Dr. Hiroki Mori, and Dr. Kazuto
Takaishi (Okayama University) for the valuable discussions.
REFERENCES
■
(1) (a) Anthony, J. E. Chem. Rev. 2006, 106, 5028. (b) Pron, A.;
Gawrys, P.; Zagorska, M.; Djurado, D.; Demadrille, R. Chem. Soc. Rev.
2010, 39, 2577. (c) Takimiya, K.; Shinamura, S.; Osaka, I.; Miyazaki, E.
Adv. Mater. 2011, 23, 4347.
(2) For reviews, see: (a) Anthony, J. E. Angew. Chem., Int. Ed. 2008, 47,
452. (b) Mei, J.; Diao, Y.; Appleton, A. L.; Fang, L.; Bao, Z. J. Am. Chem.
Soc. 2013, 135, 6724. For representative studies on the OFETs
application of picenes, see: (c) Okamoto, H.; Kawasaki, N.; Kaji, Y.;
D
Org. Lett. XXXX, XXX, XXX−XXX