Pseudodimeric Complexes of an (18-Crown-6)stilbene with Styryl Dyes Containing an Ammonioalkyl Group: Synthesis, Structure, and Stereospecific [2 + 2] Cross-Photocycloaddition

Article abstract of DOI:10.1021/acs.joc.0c02514

A new efficient method was proposed for the synthesis of (18-crown-6)stilbene; the structure of the product was confirmed by X-ray diffraction analysis. In MeCN, this compound forms pseudodimeric complexes with N-(2-ammonioethyl)-4-styrylpyridinium and N-(3-ammoniopropyl)-4-styrylpyridinium diperchlorates via hydrogen bonding between the ammonium group and the crown ether oxygen atoms. The ammonioethyl derivative was synthesized for the first time. The stability constants and spectral characteristics of the complexes were measured by spectrophotometric and fluorescence titration. Photoirradiation of the pseudodimeric complex of (18-crown-6)stilbene with the ammoniopropyl dye resulted in the stereospecific [2 + 2] cross-photocycloaddition reaction. The replacement of the stilbene moiety in the crown compound by a styrylpyridine moiety led to a 5-fold increase in the quantum yield of the photoprocess. The most probable cause for this effect is the presence of photoinduced electron transfer in (18-crown-6)stilbene complexes. This assumption is confirmed by fluorescence lifetime spectroscopy and density functional theory calculations.

Full text of DOI:10.1021/acs.joc.0c02514

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Article
Pseudodimeric Complexes of an (18-Crown-6)stilbene with Styryl
Dyes Containing an Ammonioalkyl Group: Synthesis, Structure, and
Stereospecific [2 + 2] Cross-Photocycloaddition
Timofey P. Martyanov,* Evgeny N. Ushakov, Vyacheslav N. Nuriev, Nadezhda A. Aleksandrova,
Sergey K. Sazonov, Artem I. Vedernikov, Lyudmila G. Kuz’mina, Lubov S. Klimenko,
Elena G. Martyanova, and Sergey P. Gromov*
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ABSTRACT: A new efficient method was proposed for the
synthesis of (18-crown-6)stilbene; the structure of the product was
confirmed by X-ray diffraction analysis. In MeCN, this compound
forms pseudodimeric complexes with N-(2-ammonioethyl)-4-
styrylpyridinium and N-(3-ammoniopropyl)-4-styrylpyridinium
diperchlorates via hydrogen bonding between the ammonium
group and the crown ether oxygen atoms. The ammonioethyl
derivative was synthesized for the first time. The stability constants
and spectral characteristics of the complexes were measured by spectrophotometric and fluorescence titration. Photoirradiation of
the pseudodimeric complex of (18-crown-6)stilbene with the ammoniopropyl dye resulted in the stereospecific [2 + 2] cross-
photocycloaddition reaction. The replacement of the stilbene moiety in the crown compound by a styrylpyridine moiety led to a 5-
fold increase in the quantum yield of the photoprocess. The most probable cause for this effect is the presence of photoinduced
electron transfer in (18-crown-6)stilbene complexes. This assumption is confirmed by fluorescence lifetime spectroscopy and density
functional theory calculations.
INTRODUCTION
■
The [2 + 2] photocycloaddition (PCA) reaction of
unsaturated compounds is an important photoreaction used
in synthetic organic chemistry.1 The problems of low
stereoselectivity and low quantum yields observed for
intermolecular PCA of diarylethylenes are solved by supra-
molecular self-assembly of molecules into dimer pairs with a
definite orientation of double bonds.2 Cross-PCA, which takes
thiostyryl)pyridine derivatives (E)-2, and their pseudodimeric
complexes (Scheme 1). The electron-donating capacity of
monocrown stilbene (E)-1 is somewhat lower than that of bis-
crown stilbene St, because of the absence of a second crown
ether moiety, but somewhat higher than that of styrylpyridine
analogue (E)-3.
In relation to the pseudodimeric complexes of crown-
containing styrylpyridine (E)-3 with N-ammoniopropyl styryl
dye derivatives (including dye (E)-2b), it was shown that
visible light irradiation of the complexes in solution also gives
place between different olefins, markedly expands the synthetic
potential of the reaction.3 In the case where an unsaturated
electron donor and electron acceptor are used as the starting
reactants, it is very difficult to predict the possibility and
efficiency of cross-PCA. There is only one published example
considering the competition between the intermolecular cross-
PCA reaction and photoinduced electron transfer (PET).4
That study addressed the complex formed by bis(18-crown-
6)stilbene St with diammonium styryl dye Am, in which the
unsaturated moieties of the two molecules were located close
to each other because of ditopic coordination. By photolysis of
this complex, the 1-hetaryl-2,3,4-triarylcyclobutane derivative
was obtained for the first time.
Received: October 22, 2020
Published: February 2, 2021
Previously,5,6 we have demonstrated that two-site binding of
olefins is not a necessary condition for stereospecific synthesis
of cyclobutane derivatives. This study is concerned with (18-
crown-6)stilbene (E)-1, N-ammonioalkyl (E)-4-(4-methyl-
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Scheme 1. Formation of Pseudodimeric Complexes (E)-1·
(E)-2
Scheme 2. Synthesis of Compound 4
the action of t-BuONa; the yield of the product was 60%
(Scheme 3).
Scheme 3. Synthesis of Compound (E)-1
rise to a single rctt isomer of cyclobutane derivative.6 The
occurrence of PET in these complexes is unlikely.
1
According to H NMR spectroscopy data, stilbene 1 was
isolated as the E isomer, which was evidenced by the spin−spin
coupling constants for olefinic protons (JCHCH = 16.9 Hz).
Comparison of the melting points of compound 1 (104−105
°C) with published data7 (96−98 °C) implies that the authors
probably dealt with insufficiently pure product.
Thus, the use of available diethyl benzylphosphonate 4 and
18-crown-6-containing benzaldehyde as the starting reactants,
simplicity of the synthesis, and relatively high yields of final
products make this method more convenient than the method
previously proposed in the literature, and the purity and
structure of product 1 can be regarded as more trustworthy in
our case.
Styryl dye 2a was prepared similarly to the previously
described dye 2b (Scheme 4).5 Quaternization of styrylpyr-
idine (E)-5 with 2-bromoethylammonium bromide was
conducted under mild conditions (boiling MeCN) to prevent
quaternization of sulfur. In the second step, bromide anions
Thus, it is impossible to predict with certainty whether
deactivation of the excited state via PET or cross-PCA reaction
would be possible in complexes (E)-1·(E)-2. In this study, we
synthesized for the first time styryl dye (E)-2a with an N-
ammonioethyl substituent and developed the synthesis of (18-
crown-6)stilbene (E)-1. Experiments confirmed the formation
of pseudodimeric complexes (E)-1·(E)-2 (Scheme 1) and
partial occurrence of PET in them. Long-term light irradiation
of a solution of the complex involving the N-ammoniopropyl
derivative afforded a single isomer of the cyclobutane
derivative.
Scheme 4. Synthesis of Dye 2a
RESULTS AND DISCUSSION
■
Synthesis. 18-Crown-6-containing stilbene (E)-1 was
previously synthesized from the corresponding halogenated
benzocrown ether and styrene in the presence of a palladium
catalyst.7 Considering reported data for distyrylbenzenes,8 we
proposed using the Horner−Wadsworth−Emmons reaction
for the synthesis of (E)-1. In the first step, condensation of
benzyl bromide with triethyl phosphite was carried out by a
known procedure, which gave diethyl benzylphosphonate 4 in
98% yield (Scheme 2).9
The condensation of 18-crown-6-containing benzaldehyde
with compound 4 was carried out at room temperature under
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Figure 1. Fluorescence spectra and spectrophotometric data on the steady-state photolysis of synthesized compounds in MeCN (1 cm cell): (a)
crown compound (E)-1 exposed to 313 nm light, total ligand concentration of 2.1 × 10−5 M, light intensity of 1.4 × 10−9 mol cm−2 s−1; (b) styryl
dye (E)-2a exposed to 365 nm light, total dye concentration of 2.1 × 10−5 M, light intensity of 2.7 × 10−9 mol cm−2 s−1. The blue curves are the
corrected fluorescence spectra (excitation at (a) 329 nm and (b) 347 nm); the solid black curves are the absorption spectra of E isomers; the red
curves are the absorption spectra of Z isomers; the green curves are the absorption spectra of the E−Z photostationary states (PSS).
were exchanged with perchlorate anions by treatment with
concentrated HClO4 in EtOH.
case of N-ammonioethyl derivative (E)-2a, the spectral
changes are considerably more pronounced than in the case
of N-ammoniopropyl analogue (E)-2b. Apparently, the
differences are due to the greater proximity of the pyridinium
residue to the benzocrown ether group in the case of (E)-1·
(E)-2a, due to the shorter ammonioalkyl chain of dye 2a.
Upon complex formation of dyes (E)-2a and (E)-2b with
ligand (E)-1, the dye luminescence is quenched 7.8- and 5.1-
fold, respectively (Figure 2, Tables 1 and 2). A probable cause
for the decrease in φfl is PET taking place in these complexes.
A more detailed discussion of this effect is given below. The
stability constants and the spectra of the complexes were
calculated from spectrophotometric and fluorescence titration
data by global analysis of spectral data10 using the complex
formation model that includes one equilibrium
Optical Spectroscopy. Crown-containing stilbene (E)-1
and dye (E)-2a exhibit an intense S0−S1 absorption band
(Figure 1) related to the π−π* electronic transition (similarly
for (E)-2b). Irradiation of acetonitrile solutions of these
compounds, similarly to irradiation of dye (E)-2b,6 with
absorbable light induces reversible E−Z photoisomerization.
The intensity of the long-wavelength band substantially
decreases, and the absorption maximum is somewhat blue-
shifted.
The key spectral and photochemical parameters for
compounds (E)-1 and (E)-2a,b are summarized in Table 1.
Table 1. Spectral and Photochemical Parameters of
a
Compounds (E)-1 and (E)-2a,b
K
(1)
S + D V SD
εmax×10−4
,
λmax ,
abs
fl
λmax
nm
,
Compound
M−1 cm−1
nm
φfl
φE−Z
φZ−E
where S is stilbene (E)-1, D is dye (E)-2a or (E)-2b, SD is
complex (E)-1·(E)-2a or (E)-1·(E)-2b, and K/M−1 is the
stability constant of complex SD.
Table 2 presents the stability constants for the complexes of
crown compounds (E)-1 and (E)-3 with dyes (E)-2a,b in
MeCN, as measured by absorption and fluorescence spectros-
copy. The main spectral and photochemical characteristics of
these complexes are shown in the same table.
The stability constants of the pseudodimeric complexes are
very similar and fall in the range log K = 4.4−4.5, which is
somewhat higher than the stability constant of the complex of
stilbene (E)-1 with the ethylammonium cation (log K = 4.24,
Figure S1), because of the additional stacking interactions in
the former case. The differences between the measured
constants and the stability constant of complex (E)-3·(E)-2b
are within the accuracy of measurements (Table 2).
(E)-1
(E)-2a
(E)-2b
325
407
401
2.94
3.71
3.72
383
576
571
0.064
0.33
0.26
0.39
0.22
0.27
0.40
0.48
0.42
b
a
In MeCN; λmaxabs is the peak position of the S0−S1 absorption band;
εmax is the molar absorption coefficient at λmaxabs; λmax is the peak
position in the corrected fluorescence spectrum; φfl is the fluorescence
quantum yield; φE−Z and φZ−E are the quantum yields of the forward
and reverse E−Z photoisomerization reactions, respectively. Data for
dye 2b are taken from ref 6.
fl
b
The main pathway for deactivation of the singlet excited
state of stilbene (E)-1 is E−Z photoisomerization. In the case
of styryl dyes (E)-2a,b containing a methylthio group, radiative
transition and E−Z photoisomerization make comparable
contributions to the excited state deactivation.
The complex formation of dyes (E)-2a,b with (18-crown-
6)stilbene (E)-1 was studied by spectrophotometric titration
(SPT) (Figure 2). More data on the fluorescence of complexes
were derived from the results of fluorescence titration. The
formation of pseudodimeric complexes induces small batho-
and hypochromic shifts in the absorption band of styryl dye.
Similar spectral changes were observed previously for the
complex of crown-containing styrylpyridine (E)-3 with dye
(E)-2b and were attributed to stacking interactions.6 In the
The irradiation of an acetonitrile solution of an equimolar
mixture of dye (E)-2b with crown compound (E)-1 with 405
nm light for short time periods (300 s) induced E−Z
photoisomerization of the dye (Figure S2). Long-term
irradiation of the mixture (40 h) gave rise to a new product
exhibiting characteristic cyclobutane signals at 4.5−5 ppm in
the 1H NMR spectrum (Figure S4), which indicated that cross-
PCA reaction took place (Scheme 5). This assumption was
confirmed by preparative photolysis (see Experimental Section,
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Figure 2. Spectrophotometric and fluorescence titration data for the systems (a) (E)-1−(E)-2a and (b) (E)-1−(E)-2b in MeCN (1 cm cell,
excitation wavelengths (a) 431 and (b) 424 nm): (a) 2.1 × 10−5 M (E)-2a, (b) 1.8 × 10−5 M (E)-2b; the concentration of the crown compound
varies from 0 to 7 × 10−4 M.
Table 2. Stability Constants, Spectroscopic and Photochemical Parameters for the Complexes of Crown Compounds (E)-1
a
and (E)-3 with Dyes (E)-2a,b
Complex
log K (fl)
log K (abs)
λmaxabs, nm
Δλabs, nm
εmax×10−4, M−1 cm−1
λmaxfl, nm
φfl
Φ
PCA×104
b
b
(E)-1·(E)-2a
(E)-1·(E)-2b
(E)-3·(E)-2b
4.44
4.43
−
4.45
4.44
4.48
413
403
402
+6
+2
+1
3.18
3.39
3.67
580
572
566
0.043
0.051
0.10
<0.05
3.1
14
c
a
In MeCN; log K (fl) is the logarithm of the stability constant that was measured by fluorimetry; log K (abs) is the logarithm of the stability
constant that was measured by spectrophotometry; Δλabs is the complexation-induced shift of λmaxabs; ΦPCA is the effective value of cross-PCA
b
quantum yield. The K values (M−1) are measured to within about 20%; the ΦPCA values were measured upon selective excitation of styryl dyes
c
with 405 nm light. Data for the complex (E)-3·(E)-2b were taken from ref 6; the K values (M−1) are measured to within about 30%; the ΦPCA
value was measured upon irradiation with 436 nm light (selective excitation of the dye).
However, its formation cannot be ruled out either. We
estimated the upper limit of the ΦPCA value for complex (E)-1·
(E)-2a (Table 2, Figure S10).
Scheme 5. Formation of Cyclobutane rctt-6
As follows from the results (Table 2), the quantum efficiency
of the cross-PCA reaction decreases 4.5-fold upon the
replacement of the pyridine ring in the crown component of
(E)-3·(E)-2b by a benzene ring (complex (E)-1·(E)-2b). In
order to verify the presence of a competing excited state
deactivation channel such as PET in pseudodimeric complexes
(E)-1·(E)-2, we carried out a time-resolved fluorescence
spectroscopy study. The kinetic curves for the decay of
fluorescence of free dyes (E)-2a,b correspond to a mono-
exponential decay (Figures S11, S12). For unambiguous
determination of the fluorescence lifetime τ of complex (E)-
1·(E)-2b, we carried out titration (Figure 3). The concen-
tration of crown compound (E)-1 in solution was varied, the
concentration of dye (E)-2b was invariable, and fluorescence
of the dye was monitored.
The obtained set of spectral data (Figure 3) was
satisfactorily described by the kinetic equation for biexponen-
tial decay. The titration showed that the increasing
concentration of crown stilbene (E)-1 in a solution of dye
(E)-2b is accompanied by the decreasing contribution of the
long-lived component (1.33 ns), which corresponds to the dye,
and by the increasing contribution of the short-lived
component (0.48 ns), which is apparently due to fluorescence
of the complex (Figure 4). The τ value for complex (E)-1·(E)-
2a is similar to the τ of complex (E)-1·(E)-2b.
Figure 6, and Figures S20−S26). The quantum yield of cross-
PCA reaction ΦPCA was determined by a specific procedure
described previously11 and used to determine ΦPCA for
complex (E)-3·(E)-2b (Figures S5−S8).6 The results of
measurements indicated that long-term irradiation of complex
(E)-1·(E)-2b at λ = 405 nm was accompanied by consumption
of both dye 2b and stilbene 1 (Figure S6). Photoirradiation of
the purified cyclobutane rctt-6 with 254 nm light led to the
formation of a mixture of isomers of the starting components
in acetonitrile (Figure S9). In the case of complex (E)-1·(E)-
2a, NMR study failed to unambiguously confirm the formation
of the cyclobutane derivative upon photolysis (Figure S3).
The ratio of the complex and free dye concentrations is
related to photophysical parameters by the following equation:
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steady state fluorescence spectroscopy, the parameter φr (as
well as K) was made variable.
The stability constant measured in this way (log K = 4.56)
proved to be similar to the value derived from the data on
steady-state spectroscopy (log K = 4.43); the differences are
within the accuracy of the measurements (Table 2). It is
noteworthy that the calculated ratio of the quantum yields φr
(5.4) is somewhat higher than the experimental value (5.1). If
the φr value is set to be equal to the experimental one, the
standard deviation is little affected and the stability constant
somewhat decreases (log K = 4.53).
Presumably, in the case of free dye, the rate constants for the
internal conversion and intersystem crossing for the excited
state are low in comparison with the radiative rate constant
(krad); therefore, E−Z photoisomerization with the rate
constant kiso is the only process for the nonradiative
deactivation. With the known quantum yield and fluorescence
lifetime (φfl and τ), it is possible to estimate kiso and krad using
the following relations:
Figure 3. Fluorescence decay kinetics for dye (E)-2b in the presence
of various amounts of (E)-1 in MeCN: excitation with 372 nm laser
pulse; observation at 572 nm; the blue curve is the laser pulse profile;
the colored crosses are experimental data; the solid colored curves are
from global fitting to the biexponential model Ifl(λ,t) = A1(λ) ×
exp(−t/τ1) + A2(λ) × exp(−t/τ2), with τ1 (free dye) = 1.33 ns and τ2
(complexed dye) = 0.48 ns.
τ = 1/(kiso + krad
)
φ = krad/(kiso + krad
)
fl
By substituting φfl and τ values of free dye (E)-2b, one gets
krad = φ /τ = 1.95 × 108 s−1
fl
kiso = 1/τ − krad = 5.56 × 108 s−1
The radiative lifetime 1/krad = 5.1 ns. For complex (E)-1·(E)-
2b, this gives
krad = φ /τ = 1.06 × 108 s−1
fl
The radiative lifetime 1/krad = 9.4 ns.
An almost 2-fold increase in the radiative lifetime upon
complex formation is highly unlikely, because the long-
wavelength absorption band of the dye changes insignificantly
(p S10 in Supporting Information). If we assume that the
radiative time actually does not change, φfl should amount to
0.094; i.e., it is almost twice as high as the experimental value.
A possible explanation for this contradiction is coexistence of
different conformations of the pseudodimeric complex, in
some of which the dye almost does not fluoresce, because of
the superfast deactivation of the excited state, for example, as a
result of PET (the relative content of these conformations is
slightly below 50%). A similar change in the radiative lifetime
upon complex formation was also observed for dye (E)-2a.
The question arises of how to explain the considerable (∼3-
fold) decrease in the τ value of the dye upon complex
formation. One assumption is a pronounced increase in kiso;
however, the causes behind this increase are difficult to
understand, because the form of the fluorescence spectrum of
the dye barely changes upon complex formation. One more
assumption is the formation of nonradiative exciplex with a
rate constant exceeding kiso.
Figure 4. Effect of the concentration of crown compound (E)-1 (CS)
in solution referred to the constant concentration of dye 2b (CD
=
1.86 × 10−5 M) on the partial concentration of complex (E)-1·(E)-2b
calculated from the data on the biexponential fluorescence decay
(Figure 3, eq 3); circles are experimental data, and the curve fits with
the use of one equilibrium reaction (1) of the formation of 1:1
complexes.
2
φ
A1τ1 ε2
A2τ2 ε1
[SD]
[D]
fl
=
φ 1
(2)
fl
where A1 and A2 are pre-exponential factors; ε1 and ε2 are
absorption coefficients of complex SD and dye D at the
1
2
excitation wavelength (372 nm); and φfl and φfl are the
fluorescence quantum yields for the complex and the dye at the
observation wavelength (572 nm). For the convenience of
calculations, we replaced the [SD]/[D] ratio in the left-hand
part by the partial concentration of the complex, while ε2/ε1
2
1
NMR Spectroscopic Study. The formation of pseudo-
was replaced by εr and φfl /φfl was replaced by φr:
1
dimers (E)-1·(E)-2 is confirmed by comparison of the H
[SD]
CD
1
NMR spectra of individual compounds (E)-1 and (E)-2 with
those of their equimolar mixtures in MeCN-d3. For example,
equimolar mixing of (E)-1 and (E)-2b causes upfield shifts
(ΔδH up to −0.25 ppm) of the signals of ethylene protons and
most aromatic protons of these compounds (see Figure 5; the
proton numbering is given in Scheme 1). On the contrary, the
=
1 + A2τ2/(A1τ1εrφ)
(3)
r
Using the obtained relation (eq 3), equilibrium (eq 1), and
the mass balance, we calculated the stability constant K for
complex (E)-1·(E)-2b (Figure 4). In order to check the data of
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1
Figure 5. H NMR (500 MHz) spectra (aromatic proton region) of (a) dye (E)-2b, (b) a 1:1 mixture of (E)-1 and (E)-2b, and (c) compound
(E)-1; 2 × 10−3 M, MeCN-d3.
Figure 6. 1H NMR (500 MHz) spectra (aliphatic proton region) of (a) dye (E)-2b, (b) a 1:1 mixture of (E)-1 and (E)-2b, and (c) compound (E)-
1; 2 × 10−3 M, MeCN-d3.
signals from the CH2O groups of the crown ether fragment of
cyclobutane ring protons in the 1H NMR spectrum of rctt-6 in
DMSO-d6 (Figure 7) are manifested as four doublets of
doublets. The vicinal coupling constants calculated for this
(E)-1 exhibit downfield shifts (ΔδH up to 0.1 ppm; see Figure
+
6), which indicates hydrogen bonding of the NH3 group to
the macroheterocycle.12 The signals of the (CH2)3NH3+ group
of dye (E)-2b move upfield upon complexation (ΔδH up to
−0.29 ppm, Figure 6). The upfield shifts observed upon the
formation of pseudodimeric complex (E)-1·(E)-2b testify that
the styrylpyridinium and stilbene moieties in this complex are
arranged one above the other, which results in various
anisotropic effects. Equimolar mixing of (E)-1 and (E)-2a in
MeCN-d3 led to similar changes in proton chemical shifts
(Figures S14, S15).
ABCD spin system, 3Jcis‑ab = 10.2 Hz, 3Jtrans‑bc = 7.0 Hz, 3Jcis‑cd
=
9.8 Hz, and 3Jtrans‑da = 7.6 Hz, are typical of the rctt isomers of
1,2,3,4-tetra(het)aryl-substituted cyclobutanes.4−6
X-ray Diffraction Analysis. We succeeded in growing very
small and thin single crystals of (18-crown-6)stilbene 1. The
view of the molecule in two projections is shown in Figure 8.
The stilbene moiety of the molecule is slightly nonplanar.
The dihedral angle between two benzene rings is equal to
23.8°. The dihedral angles between planes of the C1···C6 ring/
C6−C7C8−C9 moiety and C9···C14 ring/C6−C7C8−
C9 moiety amount to 10.2° and 13.7° respectively. With these
deviations from planarity, the conjugation over the stilbene
moiety is still present. The bond lengths in the C6−C7C8−
C9 moiety are 1.463(3), 1.323(4), and 1.453(3) Å. The
macrocycle adopts the typical crown-like conformation
The NOESY spectra were measured for mixtures of dyes
(E)-2a,b and crown compound (E)-1 (Figures S16−S19). All
of the observed NOE interactions were intramolecular.
As a result of preparative photolysis of an acetonitrile
solution of stilbene (E)-1 and styryl dye (E)-2b, cyclobutane
derivative 6 was isolated in a pure state. The signals of
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Figure 9. Fragment of crystal packing of (E)-1.
Figure 7. 1H NMR (500 MHz) spectrum (cyclobutane proton
region) of cyclobutane derivative rctt-6.
show the Gibbs free energies in solution (Gsoln) calculated
for various conformers of (E)-1, (E)-2a,b, and (E)-1·(E)-2.
Figure 10 presents the lowest-energy conformations of (E)-1
and (E)-2a,b, as derived from the DFT/SMD calculations.
Generally, stilbene (E)-1 can adopt two principal con-
formations (s-trans and s-cis) due to rotation around the single
bond connecting the benzocrown ether moiety to the ethylenic
bond. According to calculations, the s-cis conformer of (E)-1 is
0.98 kcal mol−1 more stable than the s-trans conformer. The
bond lengths in the CPh−CC−CAr bridge of (s-cis)-[(E)-1]
were calculated to be 1.471, 1.343, and 1.468 Å. These values
are very close to those observed for the crystalline (s-trans)-
[(E)-1] (Figure 8); the deviations between the calculated and
observed bond lengths are 0.7−1.3%.
preorganized toward binding to a metal cation and primary
ammonium ions. The mean plane through the macrocycle
oxygen atoms significantly deviates from the stilbene moiety
(see Figure 8, bottom).
The crystal packing is built of alternating doubled crown
ether and conjugated stilbene layers (Figure 9).
In the stilbene layer, any pair of adjacent molecules has a T-
shaped arrangement of the conjugated moieties (Figure S27),
which is unfavorable for the [2 + 2] photocycloaddition of an
ethylene compound.
Molecular Structure Calculations. The structures of
stilbene (E)-1, styryl dyes (E)-2a,b, and pseudodimeric
complexes (E)-1·(E)-2 in MeCN were calculated by density
functional theory (DFT). The solvation model known as
solution model density (SMD) was used to simulate solvent
effects. Computational details are presented in the Exper-
imental Section. Tables S2−S4 (Supporting Information)
The most stable conformers of styryl dyes (E)-2a,b are
characterized by s-trans orientation of the SMe group relative
to the ethylenic bond (Table S3). The s-cis conformers of (E)-
2a and (E)-2b are 1.24 and 0.18 kcal mol−1 less stable than the
corresponding s-trans conformers. The ammonioalkyl sub-
Figure 8. Structure of s-trans conformer of (E)-1 in two projections; thermal displacement ellipsoids are drawn at the 50% probability level.
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of complexes imply the coexistence of these conformers in
solution.
The distances between the centers of the double bonds for
two complexes syn-[(E)-1·(E)-2a] and syn-[(E)-1·(E)-2b]
differ little (3.454 and 3.489 Å, Figure 11) and meet the
topochemical criteria required for PCA reactions to occur.13
The angles between the ethylenic bonds in the complexes are
27.9° and 23.6°, respectively. The fact that DFT calculations
predict the predominance of the anti-conformations for
complex (E)-1·(E)-2a in solutions (Table S4) and the greater
deviation from the parallel arrangement of the bonds appears
not to be the major cause of the lower ΦPCA value compared to
that of (E)-1·(E)-2b. Presumably, in the excited state of syn-
[(E)-1·(E)-2a], the rigidity of the ammonioethyl moiety of the
dye prevents the double bonds from approaching each other.
For the lowest-energy conformers of syn-[(E)-1·(E)-2a] and
syn-[(E)-1·(E)-2b], we optimized the geometries of the S1
states (Figure S30); the distances between the centers of the
double bonds are 3.612 and 3.053 Å, respectively. The angles
between the ethylenic bonds are 15.2° and 8.4°, respectively.
Apparently, less favorable relative arrangement of the double
bonds in the excited state of (E)-1·(E)-2a compared with (E)-
1·(E)-2b is responsible for the dramatically low efficiency of
the cross-PCA reaction (Table 2). On the whole, the quantum
yield of cross-PCA for pseudodimeric (E)-1·(E)-2b and (E)-3·
(E)-2b is relatively low. The most probable explanation is the
unfavorable orientation of ethylenic bonds, i.e., a great angle
between them (∼24°).
Using time-dependent DFT (TDDFT), we calculated the
vertical electronic transition energies for the dyes and their
complexes (Table S5) and the molecular orbitals between
which these transitions take place (Table S6). The results
indicate that the long-wavelength absorption band of the
pseudodimeric complexes is associated with two transitions of
similar energy (S0−S1 and S0−S2). In the case of (E)-1·(E)-2a,
the S0−S1 transitions of the two lowest-energy conformers with
the syn- and anti-orientations of the double bonds are
completely or predominantly related to the intermolecular
electron transfer (ET) from the donor moiety (stilbene) to the
acceptor one (dye). In this case, the photoexcitation to the
long-wavelength absorption band of the complex may be
followed by internal conversion from the S2 state to the S1
state, which has a lower energy and is actually an ET-based
radical ion pair. While considering the electronic transitions of
complex (E)-1·(E)-2b, one can notice that the S0−S1 transition
of the lowest-energy conformer (syn-(up−sc)·(tg−st)) is not
Figure 10. Most stable conformers of crown compound (E)-1 and
dyes (E)-2a,b in MeCN, according to DFT/SMD calculations.
stituent of the dye can adopt trans and gauche conformations:
in the case of (E)-2a, the lowest energy is inherent in the
gauche conformation, while in the case of (E)-2b, trans,trans
conformation has the lowest energy. Pictorial views of various
conformers of stilbene (E)-1, dyes (E)-2a,b, and their
complexes are depicted in Figure S29.
Figure 11 shows the lowest-energy conformations of
complexes (E)-1·(E)-2a,b with the syn and anti orientations
of the two ethylenic bonds with respect to each other.
Both the syn and anti conformers of complex (E)-1·(E)-2a
are characterized by gauche conformation of the ammonioethyl
group. The ammoniopropyl group in both conformers of
complex (E)-1·(E)-2b adopts a trans,gauche conformation. The
styryl dyes in complexes (E)-1·(E)-2a,b have the s-trans
orientation of the SMe group. Crown stilbene (E)-1 in the syn
and anti conformers of the pseudodimeric complexes adopts
different conformations: s-cis and s-trans, respectively. In the
case of complex (E)-1·(E)-2a, the anti conformer is more
stable than the syn conformer (the difference in Gsoln was
calculated to be 0.64 kcal mol−1), whereas, in the case of (E)-1·
(E)-2b, the syn-conformer is more stable than the anti
conformer (the difference in Gsoln is 0.91 kcal mol−1). The
small differences in Gsoln between the syn and anti conformers
Figure 11. Most stable syn and anti conformers of complexes (E)-1·(E)-2a and (E)-1·(E)-2b in MeCN, as derived from DFT/SMD calculations;
+
hydrogen atoms are hidden except those of the NH3 group.
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related to ET, but is due to electron density redistribution in
the dye. In the case of the second low-energy conformer of
(E)-1·(E)-2b, the S0−S1 transition is approximately half related
to the intermolecular ET. Apparently, the experimentally
established fluorescence lifetime of 0.48 ns corresponds to the
conformers without PET (Table 3). For other conformers for
EXPERIMENTAL SECTION
■
Melting points (uncorrected) were measured in capillaries on a Mel-
Temp II apparatus. Elemental analyses were carried out in the
Microanalytical Laboratory of the A. N. Nesmeyanov Institute of
Organoelement Compounds of the Russian Academy of Sciences
(Moscow, Russian Federation). The samples for elemental analyses
were dried at 80 °C in vacuo. NMR spectra were recorded on a Bruker
DRX500 spectrometer (1H NMR, 500 MHz; 13C NMR, 125 MHz);
chemical shifts were measured to within 0.01 ppm using the residual
solvent peak (MeCN-d3 or DMSO-d6) as the internal standard (δH
1.94, 2.50 ppm and δC 1.32, 39.52 ppm, respectively); spin−spin
coupling constants were determined with an accuracy of 0.1 Hz. ESI
mass spectra were obtained on a MicrOTOF II instrument (Bruker
Daltonics) in the range m/z = 50−3000 for positive ions (a solution
was injected in a nitrogen gas flow, voltage of 4500 V). Al2O3
(Aluminumoxid 90 active neutral, 0.063−0.200 mm, Merck) was used
for column chromatography. Reactions were monitored by thin-layer
chromatography (TLC) on DC-Alufolien Aluminumoxid 60 F254
neutral (Typ E) (Merck). All initial compounds were purchased
and used without purification. Acetonitrile (Cryochrom, special purity
grade, H2O content <0.03%, v/v) was used as received. UV−vis
absorption spectra were measured on a Specord M40 spectropho-
tometer using 1 and 0.2 cm quartz cells with ground-in stoppers.
Solutions of stilbene 1 and dyes 2a,b were prepared in a darkroom
under red light to avoid the E−Z photoisomerization that occurs upon
exposure to daylight. Steady-state fluorescence spectra were obtained
on a PerkinElmer LS 55 spectrometer; the spectra were corrected
according to the spectral sensitivity curve for the photodetector.
Photolyses were carried out using glass-filtered light (λ = 313, 365, or
405 nm) of a DRSh-250 high-pressure mercury lamp (250 W). The
313 nm spectral line was isolated with an efficiency of 99.0% using a
combination of optical filters UFS-2 (3 mm thick) and ZhS-3 (2.5
mm thick); the 365 nm line was isolated with an efficiency of >99.8%
using a combination of optical filters UFS-6 (5 mm) and BS-7 (3
mm); the 405 nm line was isolated with an efficiency of 99.4% using a
combination of optical filters ZhS-10 (5 mm) and PS-13 (3 mm). The
intensity of actinic light was measured by chemical actinometry.
Fluorescence decay curves were recorded on a FluoTime 200 system
(PicoQuant GmbH) using a pulsed diode laser as the excitation
source operating at a wavelength of 372 nm with a pulse duration of
∼75 ps.
Diethyl Benzylphosphonate (4). A mixture of (bromomethyl)-
benzene (6.6 g, 0.039 mol) and triethyl phosphite (11.6 mL, 0.070
mol) was heated under reflux with stirring for 6 h with simultaneous
distilling of bromoethane formed. Excess triethyl phosphite was
removed in vacuo for 1 h. The residue was distilled at 156 °C/10 mbar
(lit. data: bp 120 °C/1.5 mbar (1.1 mmHg)9) to give compound 4
(8.4 g, 98% yield) as a colorless liquid. H NMR (DMSO-d6, 500
MHz): δ 7.34−7.20 (m, 5H), 3.98−3.89 (m, 4H), 3.21 (d, 2H, J =
21.5 Hz), 1.16 (t, 6H, J = 7.0 Hz).
18-[(E)-2-Phenylvinyl]-2,3,5,6,8,9,11,12,14,15-decahydro-
1,4,7,10,13,16-benzohexaoxacyclooctadecine ((E)-1). A solu-
tion of compound 4 (0.20 mL, 0.97 mmol) in dry DMF (5 mL) was
added to a solution of t-BuONa (0.38 g, 3.98 mmol) in dry DMF (8
mL), and the resulting mixture was stirred under nitrogen gas flow for
40 min. A solution of 4′-formylbenzo-18-crown-6 ether (0.33 g, 0.97
mmol) in dry DMF (4 mL) was added (in portions) to the mixture
and then stirred for 75 h in the dark. The reaction mixture was diluted
with water (100 mL), and the precipitate thus formed was filtered and
then purified by column chromatography on Al2O3 using a benzene−
MeCN gradient mixture (up to 25% of the latter) as an eluent.
Compound (E)-1 was obtained in 60% yield (0.24 g) as a white
powder, mp 104−105 °C (cf. lit.:7 mp 96−98 °C). 1H NMR (MeCN-
d3, 500 MHz): δ 7.54 (d, 2H, J = 7.4 Hz), 7.37 (t, 2H, J = 7.8 Hz),
7.25 (t, 1H, J = 7.4 Hz), 7.20 (d, 1H, J = 1.8 Hz), 7.14 (d, 1H, J =
16.9 Hz), 7.09 (d, 1H, J = 16.9 Hz), 7.06 (dd, 1H, J = 8.4, 1.8 Hz),
6.91 (d, 1H, J = 8.4 Hz), 4.23−4.19 (m, 2H), 4.17−4.13 (m, 2H),
3.80−3.73 (m, 4H), 3.64−3.59 (m, 4H), 3.59−3.53 (m, 8H).
13C{1H} NMR (MeCN-d3, 125 MHz): δ 149.3, 149.1, 138.8, 131.3,
Table 3. Fluorescence Lifetimes of Styryl Dyes (E)-2a,b and
Their Complexes with Stilbene (E)-1 in MeCN
Compound
τ, ns
(E)-2a
(E)-1·(E)-2a
(E)-2b
1.44
0.46
1.33
0.48
a
b
(E)-1·(E)-2b
a
Fluorescence lifetime was obtained for mixture of 1 (7 × 10−4 M)
b
and 2a (2 × 10−5 M) (Figure S13). Fluorescence lifetime was
calculated from titration data (Figure 3).
which the state with the intermolecular ET has the lowest
energy, the excited state lifetime is substantially shorter, being
less than the laser pulse width (<75 ps). It is important that,
for the syn- and anti-conformers of the pseudodimeric complex
(E)-3·(E)-2b formed by crown-containing styrylpyridine, the
S1 state is not related to the intermolecular ET, which is also
confirmed by a slight decrease in the fluorescence quantum
yield of (E)-2b upon the complex formation with (E)-3.6
CONCLUSIONS
■
(18-Crown-6)stilbene with a high degree of purity was
prepared using the Horner−Wadsworth−Emmons reaction.
As expected, spectral features and quantum yields of E−Z
photoisomerization and fluorescence for N-(2-ammonioethyl)-
4-styrylpyridinium and N-(3-ammoniopropyl)-4-styrylpyridi-
nium dyes are quite similar. The complex formation of these
dyes with (18-crown-6)stilbene gives pseudodimeric com-
plexes with stacked molecules. Light irradiation of the complex
with the ammoniopropyl dye gave rise to a single rctt isomer of
cyclobutane. The quantum yield of this reaction proved to be 5
times lower than the quantum yield of cross-PCA for a similar
complex based on crown-containing 4-styrylpyridine. This is
apparently caused by the competing excited state deactivation
in approximately half of the conformers of the complex with
the crown-containing stilbene, namely, photoinduced electron
transfer. The other conformers show an almost 3-fold decrease
in the lifetime of the singlet excited state relative to the free
dye, which can be attributed to the formation of nonradiative
exciplexes. The low quantum yield or complete exclusion of
cross-PCA in the crown stilbene complex with the
ammonioethyl styryl dye is probably due to higher rigidity
and the small length of the ammonioalkyl chain of the N-
substituent, which prevents the ethylenic bonds of the
components from approaching each other in the excited state.
The results of the present study markedly expand the
boundary conditions for conducting the cross-PCA reactions
of diarylethylenes using the supramolecular assembly. They
will also be useful for the development of methods for the
synthesis of cyclobutane derivatives. It was shown that the
possibility of photoinduced electron transfer should be taken
into account in the consideration of the photochemistry of
heterodimeric structures of aromatic olefins.
1
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129.7, 129.4, 128.3, 127.5, 127.2, 120.8, 113.1, 110.5, 71.2, 71.1,
global analysis of time-dependent spectroscopic data has been
described previously.16
71.05, 71.03, 69.9, 69.8, 68.7, 68.6. HRMS (ESI-TOF) m/z: [M +
+
+
NH4 ] Calcd for C24H34NO6 432.2381; Found 432.2390. Anal.
Calcd for C24H30O6: C, 69.54; H, 7.30. Found: C, 69.70; H, 7.34.
1-(2-Ammonioethyl)-4-{(E)-2-[4-(methylthio)phenyl]vinyl}-
pyridinium Diperchlorate ((E)-2a). A mixture of 4-{(E)-2-[4-
(methylthio)phenyl]vinyl}pyridine (5)14 (150 mg, 0.66 mmol), 2-
bromoethylammonium bromide (162 mg, 0.79 mmol), and MeCN
(10 mL) was heated under reflux for 30 h in the dark using an oil bath
placed on a hot plate magnetic stirrer. The reaction mixture was
cooled to room temperature, and the precipitate was filtered, washed
with MeCN (3 mL), and dried in air to give the dibromide salt of the
Spectrophotometric Titration. Titration experiments were
conducted in quartz cells (1 cm path length) using MeCN as the
solvent. The total concentration of dye (E)-2 was maintained at a
constant value, and the total concentration of stilbene (E)-1 gradually
increased from zero. The absorption spectra of pure complexes (E)-1·
(E)-2 as well as the complex stability constants were derived from
fitting of the spectrophotometric titration data to a 1:1 complexation
model using the global analysis methods reported previously.10
Quantum Yields of E−Z Photoisomerization. Measurements
were conducted in MeCN solutions using quartz cells with a path
length of 1 cm. The quantum yields for the forward and reverse E−Z
photoisomerization reactions (φE−Z and φZ−E, respectively) were
obtained from the kinetics of UV−vis absorption spectra measured
upon steady-state irradiation of E isomer with 313 nm light (for 1) or
with 365 nm light (for 2a). In the case of dye 2a, the spectrum of the
initial E isomer and the spectra of the E−Z photostationary states
attained upon irradiation at different wavelengths were used to
calculate the absorption spectrum of the pure Z isomer under the
assumption that the φE−Z/φZ−E ratio does not depend on the
irradiation wavelength. In the case of crown stilbene 1, the spectrum
of the Z isomer was derived by subtracting the normalized spectrum
of the E isomer from the spectrum of the photostationary state (313
nm). The amount of the E isomer in the photostationary mixture was
estimated from the fluorescence spectrum taking into account the fact
that the Z isomer almost does not fluoresce. The treatment of
photoirradiation-dependent spectra was carried out using global
analysis methods, as described previously.11 The φE−Z and φZ−E values
were determined to within 20%.
1
dye (182 mg, 64% yield) as a yellow powder, mp 250−252 °C. H
NMR (DMSO-d6, 500 MHz): δ 8.90 (d, 2H, J = 6.8 Hz), 8.28 (d, 2H,
J = 6.8 Hz), 8.09 (br.s, 3H), 8.06 (d, 1H, J = 16.3 Hz), 7.71 (d, 2H, J
= 8.4 Hz), 7.52 (d, 1H, J = 16.3 Hz), 7.37 (d, 2H, J = 8.4 Hz), 4.76 (t,
2H, J = 5.7 Hz), 3.55−3.48 (m, 2H), 2.54 (s, 3H).
The dibromide salt (100 mg, 0.23 mmol) was dissolved in EtOH
(3 mL) at heating, conc. HClO4 (70%, aq.) (100 μL, 1.16 mmol) was
added, and the reaction mixture was cooled to room temperature. The
precipitate thus formed was filtered, washed with EtOH (2 mL) and
then with Et2O (3 mL), and dried in air to give dye (E)-2a (75 mg,
71% yield) as dark-yellow crystals, mp 222−224 °C. 1H NMR
(DMSO-d6, 500 MHz): δ 8.86 (d, 2H, J = 6.9 Hz), 8.26 (d, 2H, J =
6.9 Hz), 8.04 (d, 1H, J = 16.3 Hz), 8.03 (br.s, 3H), 7.71 (d, 2H, J =
8.5 Hz), 7.51 (d, 1H, J = 16.3 Hz), 7.36 (d, 2H, J = 8.5 Hz), 4.74 (t,
2H, J = 5.8 Hz), 3.50 (br.s, 2H), 2.53 (s, 3H). 13C{1H} NMR
(DMSO-d6, 125 MHz): δ 153.8, 144.8, 142.2, 141.0, 131.5, 128.8,
125.8, 123.8, 122.1, 56.9, 14.2. Anal. Calcd for C16H20Cl2N2O8S: C,
40.78; H, 4.28; N, 5.94. Found: C, 40.61; H, 4.37; N, 5.81.
Quantum Yields of Cross-PCA. The quantum yield of cross-
PCA for complex (E)-1·(E)-2b in MeCN was estimated from the
spectrophotometric data on the photolysis of an equimolar solution of
(E)-1 and (E)-2b (1 × 10−4 M, 0.2 cm cell) with 405 nm light
(selective excitation of dye 2b). The dye consumption in the cross-
PCA reaction was determined on the basis of spectrophotochemical
data using the specific procedure reported previously.11 The cross-
PCA quantum yield obtained in this way is an effective value, since
the complexed dye 2b is able to undergo the reversible E−Z
photoisomerization.
The upper limit of the quantum yield of cross-PCA for complex
(E)-1·(E)-2a was derived from the kinetics of the absorption spectra
observed during steady-state irradiation of the complex in solution
(30-fold excess of stilbene 1 over dye 2a) at λ = 405 nm using the
kinetic equation for irreversible unimolecular photoreactions:
1-(2-Ammoniopropyl)-4-r-{2-c-(2,3,5,6,8,9,11,12,14,15-dec-
ahydro-1,4,7,10,13,16-benzohexaoxacyclooctadecin-18-yl)-4-
t-[4-(methylthio)phenyl]-3-t-phenylcyclobutyl}pyridinium Di-
perchlorate (rctt-6). A mixture of compound (E)-1 (12.3 mg, 29.7
μmol) and dye (E)-2b (13.4 mg, 27.6 μmol) was dissolved in MeCN
(20 mL) in a glass flask and irradiated with a glass-filtered light of a
high pressure Hg lamp (λ = 405 nm, distance from the light source is
∼20 cm) for 50 h. The reaction mixture was evaporated in air to
dryness without heating. The solid residue was dissolved in MeCN
(3.5 mL) and slowly saturated with benzene vapor for 3 weeks at
room temperature. The resulting crystalline precipitate was decanted
and dried in vacuo to afford compound rctt-6 in 17% yield (4.2 mg) as
a slightly yellowish powder, mp 188−190 °C dec. 1H NMR (DMSO-
d6, 500 MHz): δ 8.76 (d, 2H, J = 6.4 Hz), 7.93 (d, 2H, J = 6.4 Hz),
7.25−7.11 (m, 9H), 7.11−7.03 (m, 4H), 6.92 (d, 1H, J = 8.4 Hz),
6.49 (d, 1H, J = 2.0 Hz), 4.83 (dd, 1H, J = 10.2, 7.6 Hz), 4.73 (dd,
1H, J = 9.8, 7.6 Hz), 4.65 (dd, 1H, J = 9.8, 7.0 Hz), 4.61 (dd, 1H, J =
10.2, 7.0 Hz), 4.56−4.49 (m, 2H), 4.13−4.02 (m, 2H), 3.96−3.86
(m, 2H), 3.84−3.74 (m, 4H), 3.74−3.68 (m, 4H), 3.68−3.59 (m,
8H), 2.41−2.19 (m, 2H), 2.37 (s, 3H), 2.17−2.02 (m, 2H). 13C{1H}
NMR (DMSO-d6, 125 MHz): δ 161.6, 146.3, 145.4, 143.1, 139.9,
136.1, 135.7, 131.7, 128.6, 128.0, 127.3, 126.1, 125.5, 120.5, 111.7,
111.6, 69.8, 69.7, 69.3, 69.2, 68.6, 68.5, 68.3, 67.2, 67.1, 57.2, 48.1,
47.4, 44.3, 42.4, 35.8, 28.2, 14.6. UV−vis (MeCN, Figure S9) λmax
∼290 sh. (ε 4500), 260 (ε 20 900), 228 nm (ε 24 400 M−1 cm−1).
HRMS (ESI-TOF) m/z: [M2+] Calcd for C41H52N2O6S2+ 350.1773;
Found 350.1768.
(1 − 10−εC (t)l
)
D
dCD(t)
dt
= ΦPCAINA−1103
l
where I is the light intensity, cm−2 s−1; NA is the Avogadro number,
M−1; ε is the molar absorptivity of the complex at the irradiation
wavelength (405 nm), M−1 cm−1; CD is the concentration of the dye
as a part of the complex; and l is the cell length, cm. The quasi-
photostationary state that was established after fast E−Z photo-
isomerization of the dye was taken as the starting point (Figure S10).
It was assumed that the observed long-wavelength absorbance is
entirely due to (E)-1·(E)-2a.
X-ray Diffraction Experiments. Single crystals of compound
(E)-1 were grown by slow evaporation of a CH2Cl2−hexane (∼1:1, v/
v) solution at ambient temperature in the dark. A crystal suitable for
X-ray structure determination was mounted on a CCD area Smart
APEX-II diffractometer under a stream of cooled nitrogen where
crystallographic parameters and intensities of X-ray reflection were
measured. The redaction of experimental data was performed using
the SAINT program.17 The structure was solved using direct
methods. The structure refinement was carried out in the anisotropic
approximation for all non-hydrogen atoms. Hydrogen atoms were put
into the calculated position and refined using the riding model. The
crystallographic parameters and parameters of structure refinement
are listed in Table S1.
Fluorescence Quantum Yields and Lifetimes. Fluorescence
quantum yields (φfl) were calculated according to the equation
φ = (φfl_rDex_rn2S)/(D nr2Sr)
ex
fl
where the subscript r refers to the reference standard (anthracene in
ethanol), Dex is the optical density at the excitation wavelength, S is
the integrated intensity of the corrected emission spectrum, n is the
refractive index of the solvent, and φfl_r = 0.28.15
Fluorescence lifetimes for free dyes and complex (E)-1·(E)-2a were
derived from global analysis of fluorescence decays observed at three
different wavelengths. The fluorescence lifetime of complex (E)-1·
(E)-2b was obtained from titration data. The general procedure of
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All the calculations were performed using the OLEX-2 software
program.18 The full set of the X-ray crystal data for (E)-1 has been
deposited at the Cambridge Crystallographic Data Centre (CCDC
2038923) deposit@ccdc.cam.ac.uk or http://www.ccdc.cam.ac.uk/
data_request/cif.
Russian Academy of Sciences, Moscow 119421, Russian
Federation; orcid.org/0000-0002-9969-5185
Vyacheslav N. Nuriev − Photochemistry Center of RAS, FSRC
“Crystallography and Photonics”, Russian Academy of
Sciences, Moscow 119421, Russian Federation; Department
of Chemistry, M. V. Lomonosov Moscow State University,
Moscow 119991, Russian Federation
Nadezhda A. Aleksandrova − Photochemistry Center of RAS,
FSRC “Crystallography and Photonics”, Russian Academy of
Sciences, Moscow 119421, Russian Federation
Sergey K. Sazonov − Photochemistry Center of RAS, FSRC
“Crystallography and Photonics”, Russian Academy of
Sciences, Moscow 119421, Russian Federation
Artem I. Vedernikov − Photochemistry Center of RAS, FSRC
“Crystallography and Photonics”, Russian Academy of
Sciences, Moscow 119421, Russian Federation
Lyudmila G. Kuz’mina − N.S. Kurnakov Institute of General
and Inorganic Chemistry, Russian Academy of Sciences,
Moscow 119991, Russian Federation
DFT Calculations. All calculations were carried out using the
Gaussian 09 program package.19 Molecular geometries were
optimized using the M06-2X functional20 and the 6-31G(d) basis
set. The universal solvation model known as solution model density
(SMD)21 was used to account for solvent effects (solvent MeCN).
The SMD calculations were performed using a value of 10 Å−2 for the
average density of integration points on the surface (the default value
is 5 Å−2). The internal option IOp(1/7 = 100) was used to tighten the
default optimization criteria 3-fold. In order to verify the nature of
stationary points as well as to compute thermochemical quantities, all
geometry optimizations were followed by harmonic frequency
calculations. A value of 0.96 was used as the scale factor for harmonic
frequencies in the thermochemical analysis. The Gibbs free energy in
solution (Gsoln) was calculated as follows:
Gsoln = Esoln + ΔGcorr
Lubov S. Klimenko − Yugra State University, Khanty-
where Esoln is the electronic energy in solution and ΔGcorr is the
thermal correction to Gsoln, including the zero-point energy. To
minimize basis set superposition errors for complexes, the Esoln values
were derived from single-point M06-2X/SMD calculations with the
larger 6-311G(2df,2p) basis set.
Mansiysk 628012, Russian Federation
Elena G. Martyanova − Institute of Problems of Chemical
Physics, Russian Academy of Sciences, Chernogolovka,
Moscow Region 142432, Russian Federation
TDDFT calculations (Tables S5, S6) were carried out at the CAM-
B3LYP/6-311G(2d,p)/SMD(MeCN) level of theory for geometries
determined by the M06-2X/6-31G(d)/SMD(MeCN) method. A
similar calculation with the M06-2X functional (Tables S7, S8)
resulted in similar parameters of electronic transitions.
Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.joc.0c02514
Notes
The authors declare no competing financial interest.
ASSOCIATED CONTENT
■
ACKNOWLEDGMENTS
sı
* Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.joc.0c02514.
■
This work was supported by the Russian Science Foundation
(project No. 19-73-00357, except X-ray diffraction study and
synthesis of (18-crown-6)stilbene and ammonioethyl deriva-
tive of styrylpyridine). Synthesis of the crown compound and
ammonioethyl dye was done in a framework of project No. 19-
13-00020 of the Russian Science Foundation. Crystallography
study was performed under financial support of the Ministry of
Science and Higher Education of the Russian Federation
(State Assignment FSRC “Crystallography and Photonics” of
RAS). The work was performed using the equipment of the
Multi-User Analytical Center of IPCP RAS.
Additional figures and tables including spectrophoto-
metric, NMR, and X-ray data (PDF)
Accession Codes
CCDC 2038923 contains the supplementary crystallographic
data for this paper. These data can be obtained free of charge
via www.ccdc.cam.ac.uk/data_request/cif, or by emailing
data_request@ccdc.cam.ac.uk, or by contacting The Cam-
bridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
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AUTHOR INFORMATION
■
Corresponding Authors
Timofey P. Martyanov − Institute of Problems of Chemical
Physics, Russian Academy of Sciences, Chernogolovka,
Moscow Region 142432, Russian Federation; orcid.org/
0000-0002-1537-9776; Email: martyanov.t@gmail.com
Sergey P. Gromov − Photochemistry Center of RAS, FSRC
“Crystallography and Photonics”, Russian Academy of
Sciences, Moscow 119421, Russian Federation; Department
of Chemistry, M. V. Lomonosov Moscow State University,
Moscow 119991, Russian Federation; Email: spgromov@
mail.ru
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