Photochemistry of supramolecular complex formed by trans-stilbene and the metal-organic coordination polymer

Article abstract of DOI:10.1016/j.ica.2013.09.048

Supramolecular adduct consisting from the metal-organic framework (MOF) [Zn₄(dmf)(ur)₂(ndc)₄] (ndc^2- is 2,6-naphtalenedicarboxylate, ur is urotropin, and dmf is N,N'-dimethylformamide) and trans-stilbene was synthesized and its photochemistry was studied. The quantum yield of trans-cis photoisomerization of stilbene in adduct (0.2) was found to be an order of magnitude higher than for crystalline trans-stilbene and comparable with that in organic solvents. The results demonstrate that the creation of MOFs adducts with organic photochroms is a prospective approach for the creation of new hybrid photochromic materials.

Full text of DOI:10.1016/j.ica.2013.09.048

Accepted Manuscript
Photochemistry of Supramolecular Complex Formed by Trans-Stilbene and the
Metal-Organic Coordination Polymer
Veronica V. Semionova, Evgeni M. Glebov, Valeri V. Korolev, Sergey A.
Sapchenko, Denis G. Samsonenko, Vladimir P. Fedin
PII:
S0020-1693(13)00533-1
http://dx.doi.org/10.1016/j.ica.2013.09.048
ICA 15676
DOI:
Reference:
Inorganica Chimica Acta
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Revised Date:
Accepted Date:
16 July 2013
19 September 2013
27 September 2013
Please cite this article as: V.V. Semionova, E.M. Glebov, V.V. Korolev, S.A. Sapchenko, D.G. Samsonenko, V.P.
Fedin, Photochemistry of Supramolecular Complex Formed by Trans-Stilbene and the Metal-Organic Coordination
Polymer, Inorganica Chimica Acta (2013), doi: http://dx.doi.org/10.1016/j.ica.2013.09.048
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Photochemistry of Supramolecular Complex Formed by Trans-Stilbene and
the Metal-Organic Coordination Polymer
Veronica V. Semionovaa, Evgeni M. Glebova,b, Valeri V. Koroleva, Sergey A. Sapchenkoc, Denis
G. Samsonenkoc,b, Vladimir P. Fedinc,b
aVoevodsky Institute of Chemical Kinetics and Combustion, Novosibirsk, 630090, Russia
bNovosibirsk State University, Novosibirsk, 630090, Russia
cNikolaev Institute of Inorganic Chemistry, Novosibirsk, 630090, Russia
Abstract
Supramolecular adduct consisting from the metal-organic framework (MOF)
[Zn4(dmf)(ur)2(ndc)4] (ndc2- is 2,6-naphtalenedicarboxylate, ur is urotropin, and dmf is N,N`-
dimethylformamide) and trans-stilbene was synthesized ant its photochemistry was studied. The
quantum yield of trans-cis photoisomerization of stilbene in adduct (0.2) was found to be an
order of magnitude higher than for crystalline trans-stilbene and comparable with that in organic
solvents. The results demonstrate that the creation of MOFs adducts with organic photochroms is
a prospective approach for the creation of new hybrid photochromic materials.
1. Introduction
Organic photochromic compounds are prospective for the development of various
photosensitive systems, such as optical media with nonlinear absorption, systems of optical
information recording, and optical switchers [1, 2]. Of special interest are compounds retaining
photochemical activity in the crystal state [3, 4]. Only a few classes of organic photochroms are
active in the crystal state. This is explained by the fact that the photochromic reaction typically
needs sufficient free volume to occur. Photochromic transformations were observed both in
polycrystalline films and in single crystals of diarylethenes [5, 6], derivatives of salicylic
aldehyde [4, 7], arylhydrazides [8], and fulgides [9]. In all these cases large free volume is not
necessary for the photochromic transformations to occur. Quite unexpected are examples of
crystal state photochromism of chromenes [10], spiropyrans [11] and spirooxazines [12]. In the
case of chromenes and spirocompounds the free volume necessary for photoisomerization is
rather high, therefore, no photochemical activity is typically observed in the crystal state. In the
mentioned examples, the free volume was provided either by cavities in the crystal packing or by
large size of any functional group of the molecule [11-12].
The advantages of crystal photochroms in comparison with those dissolved in liquids or
in polymers are easy handling and high fatigue resistance [4]. Increase in fatigue resistance is
caused by the absence of unwanted photochemical reactions, in which solvent molecules are

typically involved [13]. On the other side, the quantum yields of photochemical reactions in the
solid state are usually significantly lower than in solutions [12]. This is a challenge to create a
crystal photochromic material combining advantages of liquid state (high quantum yield) and
crystal state (high fatigue resistance).
One of the possible approaches to solve this problem is the creation of hybrid organic-
inorganic compounds [14]. Research interests in organic–inorganic hybrid photochromic
materials cover a wide range. The problems can be classified into three categories (see review
[15] and references there): (1) improving the photochromic behavior (quantum yield, duration,
response, reversibility, sensitivity, thermal stability, and wavelength coverage of absorption or
emission) of photochromophores via hybrid formation; (2) manufacturing ‘‘smart’’
photoresponsive systems with various switchable functions (chirality, luminescence, electric and
magnetic properties, catalysis, photomechanics, release/sorption, etc.) using photochromophores;
(3) exploring new families of photochromic materials with non-photochromic components. The
characteristics of photochromic hybrid materials could be superior to the characteristics of
starting compounds. E.g., electron transfer between organic and inorganic parts of the hybrid
materials based on transition metal oxides and polyoxometalates were reported to result in
improving photochromic properties [16]. Polyoxometalates incorporated into hybrid matrices are
considered as prospective systems for manufacturing of molecular optical switches and optical
memory devices [17].
The approach developing in this work is to use metal-organic coordination polymers (also
called metal-organic frameworks (MOF) [18]) for producing supramolecular compounds with
organic photochroms. MOFs are crystalline compounds comprising metal ions (or clusters, or
polynuclear fragments) coordinated to electrically neutral or negatively charged bridging organic
ligands to form one-, two- or three-dimensional structures. MOFs are widely used for synthesis
of host-guest inclusion compounds [18]. We believe that the incorporation of an organic
photochromic compound into a MOF can result in creation of photochromic material with high
resistance to photodegradation and high quantum yields. To our knowledge, compounds like that
were not reported in literature.
For preliminary experiments, a recently reported [19] metal-organic coordination
polymer Zn4(dmf)(ur)2(ndc)4], where ndc2- is 2,6-naphtalenedicarboxylate, ur is urotropin, and
dmf is N,N`-dimethylformamide (Fig. 1) and a well-known organic photochrom stilbene
(Scheme 1) were chosen. Stilbenes were used to study their phototransformations on flat surfaces
[20], in zeolites [21], crystalline cyclodextrin inclusion complexes [22] and calixarenes van der
Waals nanocapsules [23]. For reference, Fig. 2 shows UV absorption and luminescence spectra
of trans- and cis-stilbene in acetonitrile solutions. The size of the MOF channels is 10.5×10.5 Å,
2

and it fits well to stilbene. In this work, the adduct of the MOF with stilbene was synthesized,
and its photochemistry was studied.
2. Experimental
Reagents and materials. Trans- and cis-stilbene (Aldrich) were used without additional
purification. Samples for cis-stilbene photolysis in aqueous solutions ere prepared as described in
[24]. Synthesis and physical properties of the metal-organic coordination polymer
[Zn4(dmf)(ur)2(ndc)4] (further referred as MOF-1) were described in [19]. Its molecular formula
is C63H55N9O17Zn4. Liquid phase experiments were performed with high purity grade acetonitrile
("Kriokhrom", Russia) as a solvent. FT-IR grade KBr (Aldrich) was used for preparation of
pellets for solid state experiments. In several experiments, porous glass plates PS-2 (Vavilov
State Optical Institute, Russia) with average pore size 7 nm [25] were used as supports for
organic photochroms.
Synthesis of MOF-1 adduct with trans-stilbene. Supramolecular compound of MOF-1
(C63H55N9O17Zn4) and trans-stilbene (C14H12) is further referred as Adduct-1. MOF-1 (0.1 g) and
trans-stilbene in 10-fold excess (0.13 g) were placed into an ampoule, evacuated and heated to
105 ºC for 24 hrs. Acetonitrile, in which MOF-1 was insoluble, was used for washing the adduct
of the residual trans-stilbene. Then the formed adduct was wrung out between two sheets of
filter paper and dried under air. The resulted Adduct-1 appears as pale-yellow crystals. Elemental
analysis of Adduct-1 corresponds to the 3:1 ratio of trans-stilbene to MOF-1 suggesting the
empirical formula [Zn4(dmf)(ur)2(ndc)4]·3C14H12 (C105H91N9O17Zn4). Calcd. C 62.7, H 4.6, N
6.3; found C 62.4, H 4.5, N 6.2. The data of elemental analysis are in a good agreement with
single-crystal X-ray data (see below).
X-ray crystallography. Single-crystal XRD data collections of Adduct-1 were performed by
using an automated four circle Bruker–Nonius X8Apex CCD diffractometer with Mo-Ka
radiation (λ = 0.71073 Å). Absorption correction based on the intensities of equivalent
reflections was performed using the SADABS program [26]. The structures were solved by
direct method and refined on F2 by full-matrix least-squares method in the anisotropic
approximation (for non-hydrogen atoms) using SHELX-97 program package [27]. Positions of
the hydrogen atoms of 2,6-naphtalenedicarboxylate, urotropine ligands and guest trans-stilbene
were calculated geometrically and refined by the rigid model. Crystal data for
[Zn4(dmf)(ur)2(ndc)4]·3C14H12: monoclinic, P 21/n, a = 12.2950(4), b = 30.7547(10),
c = 24.7649(9) Å, β = 97.530(1)°, V = 9283.6(5) Å3, Z = 4, T = 100(2) K, ρcalc = 1.440 g cm–1,
R1 = 0.1089 (for reflections with I > 2σ(I)), GooF = 1.179. The atoms of two carboxylate groups
of the ndc2– moieties and coordinated dmf ligand are disordered over two half-occupied
3

positions. The crystallographic data and details of the structure refinements are summarized in
Table S1. Selected interatomic distances and valence angles are given in Table S2.
The single-crystal X-ray crystallography reveals that the framework structure in Adduct-1 is
similar to starting MOF-1. The 1D channels are filled with trans-stilbene molecules (3 molecules
per formula unit, Fig. 3). There are no special interactions either between the different guest
molecules or between the guest molecules and the framework.
Absence of residual solvent (acetonitrile) in the pores of MOF-1 was supported by means of
IR spectroscopy. The band of the C ≡ N triple bond stretching vibration (2240-2260 cm-1) did
not appear in the IR spectrum of Adduct-1.
Preparation of solid samples. Two types of samples were used for recording solid-state UV
absorption and luminescence spectra of trans-stilbene and Adduct-1. Samples of the first type
were KBr pellets containing dispersed target material prepared by means of standard procedure
used in the IR spectroscopy. For preparation of optically transparent pellets weighted amount of
KBr was crushed in an agate mortar, dried at a temperature of 130 °C for 12 hrs and evacuated
for 24 hrs. Then weighted amount of the target substance was finely grinded with pre-prepared
KBr and pressed at 200 atm. The prepared pellets were stored in the evacuated dessicator. A
typical example of the UV spectrum of a blank KBr pellet is shown in Fig. 4 (curve 1). In spite
of significant light scattering, pellets were transparent enough for using in the UV spectroscopy.
Samples of the second type were prepared by the impregnation of a porous glass plate with
solution of trans-stilbene in acetonitrile followed by evacuation. The UV spectrum of a blank
porous glass is shown in Fig. 4 (curve 2). The wavelength region of λ > 260 nm is available for
measurements.
Instrumental measurements. UV absorption spectra were recorded using an Agilent 8453
(Agilent Technologies) and Varian Cary 50 spectrophotometers. Luminescence spectra were
recorded using a Hitachi MFP-4 spectrofluorimeter. Elemental analyses on C, H, and N were
performed by means of a Euro EA 3000 CHN elemental analyzer (EuroVector Instruments).
FTIR spectra (KBr pellets) were recorded in the range of 4000 – 400 cm-1 on a Scimitar FTS
2000 Fourier-transform infrared spectrometer (Digilab LLC). Powder X-ray diffraction (PXRD)
data were collected with Cu-Kα irradiation on a Philips PW 1830 instrument equipped with a PW
1820 vertical Bragg-Brentano powder goniometer and a PW 1710 control unit.
Photochemical experiments. Stationary photolysis was performed using a high pressure
mercury lamp with sets of glass filters to select light with the necessary wavelengths. Assuming
homogeneous distribution of the absorbing substance in the sample, one can estimate quantum
yield of the photolysis in solid samples (Eq. 1). The characteristic feature of the samples used in
this work was the significant optical density at the excitation wavelength caused by the
4

properties of the support. The observed UV spectrum of a KBr pellet is determined by
substantial light scattering, and the observed spectrum of porous glass is caused by both of
scattering and absorption (Fig. 4). In this case, one has to take into account that only a part of
Abs
incident light (
) is absorbed by the target substance. The correction was made using Eq. 2.
(1)
IStilbene
dDλ
×V ×NA
dt
ϕ =
Abs
Stilbene
Δελ ×L×I
DStilbene
DStilbene + DSupport
Stilbene +DSupport
= I0 ×(1−10−(D
) )×
Abs
Stilbene
(2)
I
dDλ
Here
is the rate of absorption change (at the probing wavelength λ) in the course of
dt
photolysis at low conversions, V is the volume of the irradiated part of the sample; L is the
Abs
Stilbene
sample thickness; NA is Avogadro number;
is the intensity of light absorbed by trans-
I
stilbene, I0 is the incident light intensity (typically 1015 - 1016 quanta/s), DStilbene and DSupport are
the optical densities of trans-stilbene and support at the excitation wavelength (313 nm in our
experiments); and Δελ is the difference in molar absorption coefficients of initial compound and
product at the probing wavelength λ. Light intensity was measured by means of SOLO 2 power
and energy meter (Gentec EO). The value of Δελ for the solid state was taken equal to that
measured in solutions. All the values of quantum yields were found by averaging on the
experiments with four samples.
3. Results and Discussion
3.1. Photochemical processes possible for stilbene
Photochemistry of stilbene in solutions was widely studied (see e.g. review [28] and
references there). The possible photochemical reactions of trans- and cis-stilbene [23] are shown
in Scheme 1. Stilbene exhibits reversible trans-cis photoisomerization (compounds 1 and 2 in
Scheme 1), photocyclization of cis-stilbene to dihydrophenanthrene (3) followed by oxidation to
phenanthrene (4), and Diels-Alder dimerization of trans-stilbene to yield tetraphenylcyclobutane
products (5 and 6). Photoisomerization and photocyclization occur in all common organic
solvents [29, 30]. Unsubstituted stilbenes typically do not undergo photodimerization in organic
solvents [28]. However, this reaction was observed in aqueous solutions, in which stilbene
aggregates are formed starting from as low concentration as 10-6 M [24].
Before studying photochemistry of trans-stilbene in the solid state and in adduct with
MOF, it was necessary to refer to the spectral changes caused by the photolysis in solutions.
Fig. 5 shows the changes in the UV spectrum of trans-stilbene originate from its photolysis in a
5

common organic solvent (acetonitrile). On the first stage (Fig. 5a) trans-cis isomerization occurs,
which manifests itself as a decrease of absorption in the region 270-330 nm, and the isosbestic
point at 264 nm is conserved. Another manifestation of trans to cis transition is the decrease in
the intensity of luminescence (Fig. 2). Mutual trans-cis and cis-trans transitions lead to
establishing of the photostationary state (equilibrium between trans and cis isomers) [30].
Prolonged irradiation results in photocyclization of cis-stilbene to dihydrophenanthrene followed
by its oxidation to phenanthrene (Scheme 1). This process manifests itself as the appearance of
characteristic spectrum of phenanthrene with the peaks at 251, 274, 281 and 293 nm (Fig. 5b).
Yet another possible reaction in stilbene photochemistry is the formation of dimers via
Diels-Alder reaction (Scheme 1). In fact, this is a way to the photodegradation of photochromic
system additional to the formation of phenanthrene. The photodimers were detected in the case
of stilbene photolysis in aqueous solutions, but not in organic solvents [29] (it should be noted
that because of very low solubility of trans-stilbene in water, experiments in aqueous solutions
were always started with cis-stilbene). The formation of photodimers was also reported for trans-
stilbene molecules incorporated into γ-cyclodextrin [22] and into nanocapsules formed by two
calixarene molecules [23]. In all these cases photodimers were detected either by
chromatography or by NMR. In order to examine the possible formation of photodimers for the
case of stilbene incorporated into the MOF cage by means of UV spectroscopy, we firstly
performed experiments on the prolonged photolysis of cis-stilbene in aqueous solutions.
Prolonged photolysis of cis-stilbene in water monitored by UV spectroscopy (Fig. 6)
resulted in the formation a plateau in the region of 350-450 nm. For comparison, Fig. 6
demonstrates the spectra of cis-stilbene and phenanthrene. The plauteau was observed only in
aqueous solutions, but not in organic solvents. Therefore, we conclude that the formation of a
plauteau in the region of 350-450 nm is a signature of Diels-Alder photodimers (Scheme 1).
3.2. Photochemistry of stilbene in polycrystalline state
As we know, there is no information in the literature concerning the trans-stilbene
photolysis in the crystalline state. The possible photochemical activity of samples prepared by
dispersing of solid trans-stilbene into KBr pellets was examined by means of luminescent and
UV spectroscopy. Both methods demonstrated the occurrence of a photochemical reaction. The
typical results are presented in Fig. 7. Note that the initial spectrum of trans-stilbene
luminescence (curve 1 in Fig. 7a) contains resolved peaks with the maxima at 363 and 379 nm
and a shoulder in the region of 400 nm, while in the spectrum recorded in solution (curve 2 in
Fig. 2) the two peaks are not resolved. Both luminescence intensity (Fig. 6a) and UV absorption
(Fig. 6b) of the samples were decreased in the course of irradiation. The observed spectral
6

changes correspond to trans-cis isomerization and establishing of equilibrium between trans-
and cis-isomers. Spectral changes characteristic of either photocyclization or photodimerization
were not observed (see Figs. 5b and 6 for comparison). Therefore, we conclude that the reaction
of trans-cis photoisomerization is the only reaction occurring in the crystalline trans-stilbene.
Table 1. Quantum yields (ϕ) of trans-cis-isomerization of stilbene under different conditions.
Solution in
CH3CN
PS2 porous
glasses
Sample
KBr pellets
Adduct-1
0.5b
0.008
0.2
7
0.2
1
ϕ
Dporea, nm
% of reactive
molecules
100
2
40
40
aDpore is an average pore diameter for porous structures
bThe value is taken from [30].
Quantum yield of trans-cis photoisomerization was estimated using Eqs. 1, 2. The values
of the quantum yields for all the systems described in this work are collected in Table 1. The
quantum yield of polycrystalline trans-stilbene photoisomerization is rather small (about two
orders of magnitude lower than in solution). The decrease of quantum yield could be explained
using the known reaction mechanism. Photoisomerization of stilbenes occurs via short-living 90°
twisted intermediate state [31]. The attainment of the twisted state needs a sufficient free
volume. In the case of crystalline trans-stilbene, the reaction is possible only for the molecules
which are situated on the surface of small polycrystals dispersed in a KBr pellet. It is essentially
to assume that the quantum yield of trans-cis isomerization is proportional to the number of
molecules which have enough free space to react. Using this assumption, one can estimate that
the number of “active” molecules in the crystalline trans-stilbene is about 2%.
3.3. Photochemistry of Adduct-1
Photochemical properties of MOF-1 and Adduct-1 were studied using the samples
prepared by dispersing of the targeted substances in KBr pellets. MOF-1 exhibits its own
luminescence (curve 2 in Fig. 8) with the maximum at 422 nm [19]. The spectrum of MOF-1
emission is partially superimposed with that of trans-stilbene (curve 1 in Fig. 8). The emission
spectrum of the Adduct-1 (curve 3 in Fig. 8) appears as an asymmetric band with the maximum
at 405 nm and a shoulder at 390 nm. The Adduct-1 spectrum is not the sum of the spectra of
MOF-1 and trans-stilbene, which points up the significant interaction between the frame and the
guest molecules. Because the emission spectra of all the substances are superimposed, the
7

monitoring of a photochemical reaction using luminescence spectroscopy seems not possible.
The photochemical reaction of MOF-1 was monitored by means of UV spectroscopy.
MOF-1 was not changed under the prolonged irradiation, while Adduct-1 was found to be
photochemically active. Changes in the UV spectra of KBr pellets with the dispersed Adduct-1
in the course of irradiation are shown in Fig. 9. As in the case of crystalline trans-stilbene
photolysis (Fig. 7), only a decrease of the absorbance in the region 260-340 nm was observed. It
was interpreted as trans-cis isomerization of stilbene incorporated to the structure of adduct. As a
result, the equilibrium between trans- and cis-isomers under the irradiation is established. No
evidences of the further reactions (either cis-stilbene photocyclization or trans-stilbene
photodimerization, see Scheme 1) were found.
It in interesting to compare the photochemical behavior of stilbene incorporated to the
MOF cage (this work), in crystalline γ-cyclodextrin inclusion complexes [22], and in para-
hexanoylcalix[4]arene nanocapsules [23]. Trans-stilbene forming inclusion complexes with γ-
cyclodextrin was observed to exhibit photodimerization (Scheme 1) [22]. Both photocyclization
of cis-stilbene followed by phenanthrene formation and photodimerization of trans-stilbene
(Scheme 1) were observed in para-hexanoylcalix[4]arene nanocapsules [23]. In both cases,
photostationary state between trans- and cis-stilbene was established very fast (in several
minutes), and the secondary reactions were the results of prolonged irradiation (2 – 24 hrs).
Therefore, the quantum yields of the formation of products 4-6 (Scheme 1) were rather low. In
our case, the experiments on the prolonged irradiation (several hours) were not possible because
of progressive damage of KBr pellets.
The quantum yield of trans-cis isomerization of stilbene incorporated to Adduct-1 was
estimated at the initial stage of photolysis by the value of 0.2. This is a significant value, which is
an order of magnitude higher than for crystalline trans-stilbene (Table 1). For comparison, the
experiment on the photolysis of trans-stilbene impregnated to the porous glass PS-2 with the
average diameter of pores ca. 7 nm was performed. The results are shown in Fig. 10. As in the
case of crystalline trans-stilbene and Adduct-1, a decrease in the stilbene band absorbance was
observed and interpreted as the manifestation of trans-cis photoisomerization. The quantum
yield of trans- to cis- transition was estimated by the value of 0.2, like in the case of Adduct-1.
The quantum yields of stilbene trans-cis photoisomerization (Table 1) decrease in a row:
(Solvent) > (Porous glass) ∼ (Adduct with MOF) > (Crystalline state).
As it was mentioned previously, photoisomerization of stilbene needs a sufficient free volume.
That is why the lowest quantum yield is observed in the case of crystalline samples, for which
only surface reactions seems to be possible. In the cases of Adduct-1 and porous glasses we have
8

a 2.5–fold drop of quantum yield in comparison with the solvent. To explain this drop, we can
offer two tentative assumptions.
The first possible reason is geometrical. One can assume that the drop in quantum yield is
due to impossibility for all the light-excited molecules of trans-stilbene to reach the 90° twisted
intermediate state. Based on this assumption, one can estimate that ca. 40% of stilbene molecules
incorporated either to the porous glass or to the MOF cage are “active”. In the case of porous
glass, the average pore diameter is large enough (7 nm [24], while the geometrical size of the
plane trans-stilbene molecule is ca. 11×5 Å). Nevertheless, the structure of porous glass is not
regular. Because of this, certain of the trans-stilbene molecules embedded to the pores can
occupy positions which probably are not favorable for the formation of the twisted state. In the
case of Adduct-1, the structure of the compound is regular (Fig. 3). In this case, one can propose
that only the molecule of trans-stilbene which is situated between two others has a favorable
possibility for isomerization.
The second possible reason of the quantum yield drop seems to be the interaction
between the guest and host molecules, which can change the rates of different photophysical
processes (e.g., speeds up the internal conversion).
4. Conclusion
In this work, supramolecular adduct of trans-stilbene and a metal-organic framework was
synthesized. Stilbene was used as a cheap, readily available and well-studied substance for
preliminary experiments. The synthesized adduct was found to demonstrate significant
photochemical activity. Quantum yield of stilbene trans-cis isomerization in the adduct is of the
same order of magnitude as in solution and much higher than for the crystalline trans-stilbene.
We believe that the results demonstrate the perspectivity of the chosen approach to create hybrid
photochromic materials. The next step will be the creation of MOF adducts with another organic
photochroms characterized by high colorability and stability of the photoinduced form.
Appendix A. Supplementary material
CCDC 950294 contains the supplementary crystallographic data for Adduct 1. These data
can be obtained free of charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associated with this article can be
found, in the online version, at http://dx.doi.org/XXXXXXX.
Acknowledgement
The work was supported by the Russian Foundation of Basic Research (grants №№ 11-
03-00268 and 11-03-92605-RS).
9

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11

Figure captions
Scheme 1. Photochemical reactions of stilbenes.
Figure 1. Fragment of the framework MOF-1 structure (wire presentation). View along a axis.
Hydrogen atoms are omitted for clarity.
Figure 2. Absorption and luminescence spectra of trans-stilbene (curves 1 and 2) and cis-
stilbene (curves 3 and 4) in acetonitrile.
Figure 3. Fragment of Adduct-1 structure (wire presentation). View along a axis. Hydrogen
atoms are omitted for clarity.
Figure 4. UV spectra of a 0.045 cм thick KBr pellet (curve 1) and a porous glass PS-2 (curve 2).
Figure 5. Changes in the UV spectrum caused by trans-stilbene photolysis (313 nm) in CH3CN.
1 cm cell, initial concentration 3.5×10-5 M. (a) – initial stage of photolysis interpreted as trans-
cis isomerization. Curves 1-7 correspond to 0; 7; 13; 20; 30; 45; 70 s of irradiation. (b) –
prolonged photolysis interpreted as transition of cis-stilbene to phenanthrene. Curves 8-11
correspond to 230; 650; 1300; 2400 s of irradiation.
Figure 6. UV absorbtion spectra in aqueous solutions: cis-stilbene (1), phenanthrene (2), and the
product of the prolonged (2 hrs at 313 nm) cis-stilbene photolysis (3). 1 cm cell, natural content
of oxygen.
Figure 7. Photolysis (313 nm) of trans-stilbene in KBr pellets. (a) – changes in the luminescence
spectrum. Curves 1-4 correspond to 0; 300; 900; 2100 s of irradiation. (b) – differential changes
in the UV spectrum. Curves 1-4 correspond to 20; 50; 100; 1400 s of irradiation (samples for a
and b were different).
Figure 8. Luminescence spectra of trans-stilbene (1), MOF-1 (2) and Adduct-1 (3) in KBr
pellets.
Figure 9. Differential changes in the UV spectrum caused by irradiation (313 nm) of Adduct-1.
Curves 1 - 5 correspond to 5; 10; 40; 100; 700 s of irradiation.
Figure 10. Differential changes in the UV spectrum caused by irradiation (313 nm) of trans-
stilbene in porous glass PS-2. Curves 1 - 5 correspond to 5; 10; 40; 100; 700 s of irradiation.
12

hν
1
2
hν
hν
3
H
H
5
[O2]
4
6
Scheme 1
13

Figure 1
14

4
3
2
1
0
4
3
1
2
2
3
1
4
0
200
300
400
λ, nm
Figure 2
15

Figure 3
16

3
2
1
0
2
1
200
300
400
500
600
λ, nm
Figure 4
17

7
1,2
0,8
0,4
0,0
a
1
1
7
200
250
300
350
λ, nm
1,2
0,8
0,4
0,0
b
11
8
200
250
300
350
λ, nm
Figure 5.
18

1,0
0,8
0,6
0,4
0,2
0,0
2
Photodimer
3
1
200
300
400
500
λ, nm
Figure 6
19

3
2
1
0
a
1
4
350
400
450
500
λ, nm
0,00
-0,05
-0,10
-0,15
1
b
4
270
300
330
360
λ, nm
Figure 7
20

3
4
2
0
2
1
350
400
450
500
550
600
λ, nm
Figure 8
21

0,0
-0,2
-0,4
-0,6
1
2
3
4
5
250
300
350
400
λ, nm
Figure 9
22

0,0
-0,3
-0,6
-0,9
1
2
3
240
270
300
330
360
λ, nm
Figure 10
23

Table 1. Quantum yields (ϕ) of trans-cis-isomerization of stilbene under different conditions.
Solution in
CH3CN
PS2 porous
glasses
Sample
KBr pellets
Adduct-1
0.5b
0.008
0.2
7
0.2
1
ϕ
Dporea, nm
% of reactive
molecules
100
2
40
40
aDpore is an average pore diameter for porous structures
bTaken from [30].
24

hν
MOF cage
MOF cage
Graphical abstract
25

Photochemically active adduct of the metal-organic framework (MOF) and trans-stilbene was
synthesized. Quantum yield of stilbene trans-cis isomerization in the MOF cage is on order of
magnitude higher than for crystalline state.
Synopsis
26

•
•
•
•
Adduct of the metal-organic framework (MOF) and trans-stilbene was synthesized.
Three independent trans-stilbene molecules are located in one MOF cage.
Stilbene is a subject of photochemical trans-cis isomerization in the MOF cage.
Quantum yield of the cage reaction is much higher than for crystalline state.
27