Mendeleev Commun., 2019, 29, 229–231
1
0
0
0
.0
.8
.6
.4
.2
1
,3
0.35
Me
N
0
0
0
0
0
0
.30
.25
.20
.15
.10
.05
2
Me Me
1
3
N
O
NO2
Me
300 400 500 600 700 800
CF3CO2H
l/nm
2
Me
N
NO2
0
0
Me Me
1
a
.0
3
light yellow
00
400
500
600
700
800
N
HO
l/nm
Me
CF3CO2
Figure 1 Normalized absorption spectra for compound 1a in toluene:
1) initial solution, (2) after TFA-induced isomerization and (3) after further
(
treatment with Et N. Inset: the corresponding absorption spectra for the model
spiropyran 3.
3
2
a
dark yellow
Me
N
NO2
After addition of trifluoroacetic acid (TFA), the isomerization
of spiropyran moieties in hybrids 1a–c results in protonated
merocyanine compounds 2a–c (Scheme 1). As a model for
comparison, we chose the spiropyran 3 (Scheme 1), which did
undergo pyran ring opening both under photoexcitation and on
treatment with TFA.
Me
Me
Et3N
N
O
Me
–
Et3NH CF3CO2
Similar to the model spiropyran 3, the hybrid compound 1a
was converted, on treatment with TFA, to the protonated mero-
cyanine 2a, which showed a new band at 415 nm in the absorp-
tion spectrum (Figure 1). Merocyanine 4, obtained by the similar
treatment of spiropyran 3, gave rise to an absorption peak at
blue
Scheme 2
4
40 nm (inset in Figure 1). Treatment of protonated merocyanines
Since TFA-induced isomerization of the spiropyran moieties
in the hybrids 1a–c and the photoinduced isomerization of com-
pound 1a are reversible processes and the synthesized compounds
are stable against photodegradation, these hybrid derivatives of
nanosized carbon clusters, in our opinion, are promising active
components for multi-resistor electric switches.
2a and 4 solutions with triethylamine afforded the starting spiro-
14
pyrans 1a and 3, respectively. According to the published data,
the conversion of merocyanine 4 to spiropyran 3 proceeds via the
formation of another intermediate merocyanine structure as a
result of deprotonation of phenolic hydroxyl group. The forma-
tion of intermediate merocyanine after treatment of compound 4
with triethylamine was evidenced by an absorption peak at 580 nm
This work was supported by the Grants of the President of the
Russian Federation (nos. MK-3058.2018.3 and NSh- 5240.2018.3)
and Budget theme (AAAA-A17-117012610065-2). The structural
investigations were performed with assistance of Collective Usage
Centre ‘Agidel’ at the Institute of Petrochemistry and Catalysis
of the Russian Academy of Sciences.
(inset in Figure 1, curve 3).
Spiropyran ring opening in the hybrid molecule 1a, like that
for the model spiropyran 3, was confirmed by NMR data. The
TFA-induced isomerization for compound 3 was detected by
a downfield shift (from 2.4 to 4.0 ppm) of the signal for the
methyl group at the indole nitrogen atom (Figure S1, see Online
1
Supplementary Materials). The H NMR spectrum of the hybrid
Online Supplementary Materials
compound 1a (Figure S2) exhibited not only the TFA-induced
downfield shift for methyl group at the indole nitrogen (from 2.6
to 3.6 ppm), but also broadening of the signal of the methyl group
at the pyrrolidine ring fused to the fullerene core (~2.9 ppm),
which was apparently caused by the formation of a quaternary salt
Supplementary data associated with this article can be found
in the online version at doi: 10.1016/j.mencom.2019.03.039.
References
1 A. R. Tuktarov, A. A. Khuzin and U. M. Dzhemilev, Russ. Chem. Rev.,
2
017, 86, 474.
at the pyrrolidine moiety. Upon neutralization of TFA with Et N,
3
1
2 V. A. Barachevsky, Org. Photonics Photovolt., 2015, 3, 8.
the initial H NMR spectra were restored (Figures S1 and S2).
3
4
R. Klajn, Chem. Soc. Rev., 2014, 43, 148.
J.-F. Zhi, R. Baba, K. Hashimoto and A. Fujishima, Chem. Lett., 1994,
After treatment of compounds 3 and 1a with TFA, the cor-
responding protonated merocyanines 4 and 2a are formed in
quantitative yield, whereas the photoinitiated transformation
of spiropyranes to merocyanines proceeds in not more than
2
3, 1521.
5 J. F. Zhi, R. Baba, K. Hashimoto and A. Fujishima, J. Photochem.
Photobiol., A, 1995, 92, 91.
6 X. Song, J. Zhou, Y. Li and Y. Tang, J. Photochem. Photobiol., A, 1995,
1
4
2
0% yield. Presumably, the TFA-induced pyran ring opening
9
2, 99.
in molecules of 3 and 1a occurs as a result of deactivation of
7
8
J.-H. Xu, Y.-L. Li and D.-B. Zhu, Synth. Commun., 2002, 32, 1647.
S. Yagi, S. Nakamura, D. Watanabe and H. Nakazumi, Dyes Pigm., 2009,
80, 98.
1
4,30
the nucleophilic phenol oxygen atom upon protonation.
Neutralization of TFA with an equimolar amount of Et N
3
liberates the nucleophilic phenoxide anion and, as a consequence,
gives the starting spiropyran (Scheme 2).
Similar results have been obtained for hybrid compounds 1b
and 1c with Cl and F atoms, respectively, in the spiropyran
9 T. A. Darwish, R. A. Evans, M. James, N. Malic, G. Triani and T. L.
Hanley, J. Am. Chem. Soc., 2010, 132, 10748.
0 T. A. Darwish, R. A. Evans, M. James and T. L. Hanley, Chem. Eur. J.,
1
1
2
011, 17, 11399.
1 D. A. Davis, A. Hamilton, J. Yang, L. D. Cremar, D. Van Gough, S. L.
Potisek, M. T. Ong, P. V. Braun, T. J. Martínez, S. R. White, J. S. Moore
and N. R. Sottos, Nature, 2009, 459, 68.
moiety instead of the NO group. Although hybrids 1b and 1c
2
did not undergo photoinduced isomerization, treatment of their
solutions with TFA resulted in stable protonated merocyanines
12 Y. Shiraishi, M. Itoh and T. Hirai, Phys. Chem. Chem. Phys., 2010, 12,
2
b and 2c (see Online Supplementary Materials).
13737.
–
230 –
Tuktarov, Airat R.
