178
V. A. AZOV
Figure . (a) Interconversion of four different isomers of 3a. Relative content of each isomer after equilibration ( °C, CDCl) is shown as mol-%. (b) Optimized molecular
structures of the four isomers of 3a (BLYP/-G∗).
groups with similar spectral characteristics defined by Z- or these goals, reliable methods for the efficient and selective func-
E-configurations of the AB moiety, whereas trans-isomers dis- tionalization of the lower rim of the TTF-modified calixarenes
play characteristic AX pattern of the Ar-CH2-S bridges in NMR should be developed. Chemical modifications of the azobenzene
spectra.
moiety of TTF-AB macrocycles, such as fluorination, should
When left to stay at elevated temperatures, each of the four afford better separation of its absorptions bands from the ones
isomers slowly equilibrates to the same isomer mixture with of the TTF group and allow for selective optical switching of the
identical isomer composition. Overall, the equilibration of AB is AB unit. As an ultimate goal, we would like to immobilize TTF-
rather fast, with the approximate isomerization half-life of sev- AB macrocycles on surfaces and test their switching behavior on
eral hours at 40°C in CDCl3. The rate of the isomerization of a single molecule level.
the TTF moiety is slower and solvent-dependent: whereas in
CDCl3 at 40°C TTF isomerization half-life is around 2–3 days,
it is much longer in DMSO-d6 or in C6D12. Quite unusual for
AB derivatives, the most stable isomer trans-Z-3a contains AB
moiety in Z-configuration.
ORCID
DFT-optimized molecular structures of Z-isomers exhibit a
distorted nonplanar TTF. On the contrary, in E-isomers the TTF
moiety is fully planar, whereas the azobenzene moiety is, in turn,
significantly bent (Figure 4b). Cyclic voltammetry has shown
that the oxidation potential of structurally rigid TTF-AB macro-
cycle 3a strongly depends on the conformation of the azoben-
zene moiety, opening the way for the modulation of redox prop-
erties by an optical stimulus and design molecular devices with
orthogonal write (optical) and read (electrical) modes. DFT cal-
culations gave evidence that the out-of-plane distortion of the
TTF moiety in the macrocycle 3a is responsible for the varia-
tion of its oxidation potential upon photoisomerization of the
AB bridge.
References
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Conclusions
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To summarize, we have shown that tetrathiafulvalenes have
great potential for application in molecular architectures rang-
ing from molecular receptors to functional macrocycles com-
prising two orthogonally-controllable switchable elements. In
future, we would like to focus more on practical applications of
the designed molecular systems.
As a possible development of the TTF-calix[4]arene receptor
project, we see their application as electrochemical sensors, in
the creation of redox-controllable supramolecular materials, or
as a basis for the redox-controllable molecular Velcro. To achieve
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