Synthesis, spectroscopic characterization and photophysical investigations of new di-(2/3)-pyridine-stilbenes; isomerism, nitrogen position influence and solvent effects

Article abstract of DOI:10.1016/j.molstruc.2018.06.005

Stilbene analogues with the pyridine ring, that is di-(pyridin-2/3/4-yl)vinyl)benzenes, were synthesized, purified and completely spectroscopically characterized. Upon irradiation these di-(pyridin-3/4-yl)vinyl)benzenes showed no other process but isomerization, in conditions for both intra- and intermolecular reactions. Compound di-(pyridin-2-yl)vinyl)benzene gave by intermolecular cycloaddition reaction, in trace amounts, a dimeric product. This general unreactivity towards photocyclization and photocycloaddition reactions led to further investigations and description of photophysical properties. Quantum yields of photolysis as well as fluorescence were measured and calculated. It was shown that the placement of the nitrogen in the stilbene like system plays an important role in the photophysical properties. The connection between photophysical properties and configurational isomerism was defined. The polarity effect of the medium has a complex influence on the photobehaviour and the measured effects are probably not coming only from polarity.

Full text of DOI:10.1016/j.molstruc.2018.06.005

Accepted Manuscript
Synthesis, spectroscopic characterization and photophysical investigations of new di-
(2/3)-pyridine-stilbenes; isomerism, nitrogen position influence and solvent effects
Ivana Šagud, Valentina Milašinović, Krešimir Molčanov, Željko Marinić, Irena Škorić
PII:
S0022-2860(18)30706-3
10.1016/j.molstruc.2018.06.005
MOLSTR 25292
DOI:
Reference:
To appear in: Journal of Molecular Structure
Received Date: 5 April 2018
Revised Date: 30 May 2018
Accepted Date: 1 June 2018
Please cite this article as: I. Šagud, V. Milašinović, Kreš. Molčanov, Ž. Marinić, I. Škorić, Synthesis,
spectroscopic characterization and photophysical investigations of new di-(2/3)-pyridine-stilbenes;
isomerism, nitrogen position influence and solvent effects, Journal of Molecular Structure (2018), doi:
10.1016/j.molstruc.2018.06.005.
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ACCEPTED MANUSCRIPT
Synthesis, spectroscopic characterization and photophysical investigations
of new di-(2/3)-pyridine-stilbenes; isomerism, nitrogen position influence
and solvent effects
Ivana Šagud[a], Valentina Milašinović[b], Krešimir Molčanov[b], Željko Marinić[c] and Irena Škorić *[a]
aDepartment of Organic Chemistry, Faculty of Chemical Engineering and Technology, University of Zagreb,
Marulićev trg 19, 10000 Zagreb, Croatia, bDepartment for Physical Chemistry, Rudjer Boškovic Institute, Bijenicka
54, 10000 Zagreb, Croatia, cNMR Center, Rudjer Bošković Institute, Bijenička cesta 54, 10000 Zagreb, Croatia
Graphical abstract
Abstract
Stilbene analogues with the pyridine ring, that is di-(pyridin-2/3/4-yl)vinyl)benzenes, were
synthesized, purified and completely spectroscopically characterized. Upon irradiation these
di-(pyridin-3/4-yl)vinyl)benzenes showed no other process but isomerization, in conditions
for both intra- and intermolecular reactions. Compound di-(pyridin-2-yl)vinyl)benzene gave
by intermolecular cycloaddition reaction, in trace amounts, a dimeric product. This general
unreactivity towards photocyclization and photocycloaddition reactions led to further
investigations and description of photophysical properties. Quantum yields of photolysis as
well as fluorescence were measured and calculated. It was shown that the placement of the
nitrogen in the stilbene like system plays an important role in the photophysical properties.
The connection between photophysical properties and configurational isomerism was defined.
The polarity effect of the medium has a complex influence on the photobehaviour and the
measured effects are probably not coming only from polarity.
1. Introduction
Study of the excited state behavior of hetero-stilbene and hetero-butadiene compounds has
been a long standing interest of our group [1-12]. Our research has been based on
intramolecular photocycloaddition [1-3, 9-12] and photocyclization reactions [10]. The

ACCEPTED MANUSCRIPT
driving force behind this vast scope of research was the ease of access to a library of
polycyclic products. These different polycyclic skeleta are hard to synthesize in the ground
state organic synthesis. The benzobicyclo[3.2.1]octadiene skeleton would be a star
representative of this acquired group of polycyclic photoproducts, as this very skeleton is
found in numerous biologically active natural compounds [13-15]. In the course of our
research this moiety, with different heterocycles incorporated into it [1-12], has been
synthesized as well as further modified [16]. An interesting subgroup of compounds that was
synthesized and their excited state behavior studied are the di-hetero-stilbenes (figure 1) [17-
25]. For this group of compounds the study of photophysical properties was conducted and
published in collaboration with the A. Spalletti group in Italy, as well as O. Horváth group in
Hungary [17-28].
Figure 1. Previously studied di-hetero-stilbene derivatives [17-25].
Heterocyclic nuclei that were used to replace one of the benzene cores were furan and
thiophene. In the case of furan derivatives research was even further expanded to compounds
where the furan core was 2,5-disubstituted with vinyl-benzene moiety (figure 1). These
compounds reacted both by intra- and intermolecular photocycloaddition reactions.
Specifically, 2-(benzo/naphtho)furyl derivatives [24] gave products of cycloaddition in dilute
solutions (3x10-3 mol/L) and in more concentrated solution (3 x 10-1 mol/L) they gave
cyclophanes as products of intermolecular cycloaddition. The 2- and 3-thienyl [25]
derivatives showed analogue behavior to the furyl derivatives with the addition of
electrocyclization products that were formed in diluted solutions. The photophysical studies
were done on the 2,3-disubstituted [17-23] and 2,5-disubstituted furan derivatives [17, 26-28].
In the light of these fruitful and interesting results that were obtained we decided to
incorporate a new heterocyclic ring into the distilbene system.

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As a part of another subgroup of hetero-stilbene compounds that we are studying the pyridine
ring was incorporated into the o-vinyl stilbene system. Compounds with this 6-membered,
nitrogen containing ring displayed a whole new path of reactivity which we described and
published recently (scheme 1) [29].
Scheme 1. Photoreactivity of pyridyl-o-vinylstilbenes
Going even further by adding a new conjugated double bond to the system we obtained new
o-vinyl-pyridyl-butadiene derivatives that on irradiation gave new tricyclic and tetracyclic
products (scheme 2) [30]. These compounds are being extensively studied further for
biological activity especially the structures with the mentioned benzobicyclo[3.2.1]octadiene
moiety [13-15].
Scheme 2. Photoreactivity of pyridyl-o-vinylbutadienes.
All of this past research gave us a solid foundation for expansion of the studies on the di-
hetero-stilbenes subgroup by incorporating the pyridine ring into the system and thus
obtaining the 1,2-di-pyridyl-benzenes (1-3) (figure 2).

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Figure 2. Synthesized 1,2-di-(2/3/4)-pyridylbenzenes.
These new compounds were primarily synthesized to test their viability in the reactions of
intra- and intermolecular photocycloaddition but the research was expanded to a more in
depth investigation of photophysical properties depending on the isomerism, nitrogen position
influence and solvent effects.
2. Experimental section
2.1. General remarks
Commercially available Petroleum ether (PE), bp 50-70 ºC, was used. Solvents were purified
by distillation. The solvents were removed on the rotary evaporator under reduced pressure in
a ventilated hood. 2/3/4-pyridinecarbaldehydes were obtained from commercial sources
(Aldrich). Column chromatography was carried out on columns with silica gel (Fluka 60 Å,
technical grade). TLC was carried out using plates coated with silica gel (0.2 mm, Kiselgel 60
F254). Organic layers were dried with anhydrous MgSO4 and evaporated using a rotary
evaporator under reduced pressure. 1H and 13C NMR spectra were recorded on a spectrometer
at 600 MHz. NMR spectra were measured in CDCl3 and acetone-d6 using tetramethylsilane
(TMS) as reference. The assignments of the signals are based on 2D-CH correlations and 2D-
HH-COSY correlations. The following abbreviations were used: Sh – shoulder (in UV
spectra), s - singlet; d - doublet; t - triplet; q - quartet, dd - doublet of doublets; m - multiplet
and br - broad, PE – petroleum ether, E – diethyl ether. UV spectra were measured on a 50
Cary UV/VIS spectrophotometer. For the measurement of fluorescence and excitation spectra
a Cary Eclipse spectrofluorimeter was used. IR spectra were recorded on a FTIR-ATR and
FTIR. Mass spectra were obtained on a GC-MS system on a Varian CP-3800 Gas
Chromatograph-Varian Saturn 2200 mass spectrometer equipped with FactorFour Cappilary
Column VF-5ms, 30mx0.25mm. Melting points were obtained using a microscope equipped
apparatus and are uncorrected. HRMS analysis were carried out on a mass spectrometer
(MALDI TOF/TOF analyzer), equipped with Nd:YAG laser operating at 355 nm with firing
rate 200 Hz in the positive (H+) or negative (-H) ion reflector mode. Irradiation experiments
of compound solutions were performed in tightly closed vessels in a photochemical reactor
(Rayonet and Luzchem) equipped with the UV lamps (300 and 360 nm).

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2.2. Preparation of the 2/3/4-dipiridylbenzenes
Pyridine derivatives of distyrylbenzene 1-3 where synthesized by a modified, “one-pot”
Wittig reaction [31] (scheme 3).
Scheme 3. „One-pot“ Wittig reaction.
To a stirred solution of diphosphonium salt of α,α’-o-xylenedibromide (1 eq, 7.06 mmol) in
absolute ethanol (100 ml, 3Å sieves) the corresponding pyridinecarbaldehyde (4) (2 eq, 14.12
mmol) and the solution of sodium ethoxide (prepared in situ from 15.54 mmol, 2.2 equiv in
30 mL of ethanol) were added dropwise. Reaction mixture was left to stir for 5 h. After
removal of ethanol the residue was worked up with ice-water, and extracted with toluene (5 ×
40 mL). Toluene extracts were dried over anhydrous MgSO4. Multiple column, as well as thin
layer, chromatographies were essential to separate the isomers. There was an additional
difficulty in purification because the compounds have a similar Rf value to the side product of
the Wittig reaction, the triphenylphospine oxide. The 2-pyridyl derivative 1 gave only a
mixture of cis,trans- and trans,trans-isomer, while the 3- and 4-pirydyl (2 and 3) gave
mixtures of all of the three geometrical isomers. The 1-((E)-2-(pyridin-4-yl)vinyl)-2-((E)-2-
(pyridin-4-yl)vinyl)benzene (E,E-3) has been already extensively photophysically studied [32-
34] and investigated for template-directed solid state dimerization reaction [35], but only
1
spectroscopically described by partial H NMR spectra [32] so we have given here a full
spectroscopical characterization of this compound too along with the data for all of the new
compounds (see also supporting information file 1).
1,2-bis(2-(pyridin-2-yl)vinyl)benzene (1) (1.59g, 79%)
1-((Z)-2-(pyridin-2-yl)vinyl)-2-((E)-2-(pyridin-2-yl)vinyl)benzene (Z,E-1) as colorless
powder: mp = 116 – 120 °C; Rf (PE/EtOH 9.5:0.5) = 0.6; UV (EtOH) λmax/nm (ε
/dm3mol-1cm-

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1): 262 (10730), 270 (10735), 310 (9212); UV (n-hexane) λmax/nm (ε/dm3 cm-1mol-1): 267
(10628), 310 (10583), 319 (10194); IR νmax/cm-1 (NaCl): 2924, 1638, 1363; 1H NMR (CDCl3,
600 MHz) δ/ppm: 8.58 (d, 1H, JPy = 4.6 Hz, H-Py1t), 8.45 (d, 1H, JPy = 4.8 Hz, H-Py1c), 7.78
(d, 1H, Jet= 16.2 Hz, H-ett1), 7.72 (d, 1H, JPy.= 7.7 Hz ,H-Py4c), 7.67-7.63 (m, 2H, H-Py3t, Ar),
7.38 (d, 1H, JPy = 8.1 Hz, H-Py4t), 7.33-7.30 (m, 2H, H-Py3c, Ar), 7.18 (d, 2H, JAr = 4.2 Hz,
H-Ar), 7.14 (dd, JPy = 7.1 Hz, JPy = 4.6 Hz, 1H, H-Py2t), 7.10 (d, Jet = 16.2 Hz, 1H, H-ett2),
7.09 (d, Jet = 12.2 Hz, 1H, H-etc1), 6.99 (dd, JPy = 7.1 Hz, JPy = 4.8 Hz, 1H, H-Py2c), 6.89 (d,
Jet = 12.2 Hz, 1H, H-etc2); 13C NMR (CDCl3, 150 MHz)
δ/ppm: 155.9 (s), 155.7 (s), 149.6 (d,
C-Py1t), 149.4 (d,C-Py1c), 136.5 (s), 136.4 (d, C-ar), 135.4 (d, C-ar), 135.1 (s), 132.5 (d, C-
etc2), 132.2 (d, C-etc1), 130.6 (d, C-ett1), 130.1 (d, C-ett2), 129.7 (d, C-ar), 128.2 (d, C-ar),
127.9 (d, C-Py3c), 126.2 (d, C-Py4c), 123.8 (d, C-Py2c), 122.1 (d, C-Py4t), 121.8 (d, C-Py3t),
121.7 (d, C-Py2t); HRMS (MALDI-TOF/TOF) (m/z) for C20H16N2 (M + H)+ calcd 284.1315
found 284.1313.
1-((E)-2-(pyridin-2-yl)vinyl)-2-((E)-2-(pyridin-2-yl)vinyl)benzene (E,E-1) as oil: Rf
(PE/EtOH 9.5:0.5) = 0.55; UV (EtOH) λmax/nm (ε
/dm3mol-1cm-1): 227 (18947), 237 (Sh,
14272), 275 (Sh, 26256), 312 (45670); UV (n-hexane) λmax/nm (ε
/dm3mol-1cm-1): 275 (Sh,
1
24805), 309 (34780); H NMR (CDCl3, 600 MHz)
δ
/ppm: 8.61 (d, 1H, JPy = 4.6 Hz, H-Py4),
7.89 (d, 1H, Jet = 15.6 Hz, H-et1/2), 7.68-7.64 (m, 1H, H-ar2), 7.39 (d, 1H, JAr = 8.2 Hz ,H-ar1),
7.23-7.19 (m, 2H, H-Py1,3), 7.15 (dd, 1H, JPy = 1.0 Hz, JPy = 2.7 Hz, H-Py2), 7.07 (d, 1H, Jet =
15.6 Hz, H-ett1/2).
1,2-bis(2-(pyridin-3-yl)vinyl)benzene (2) (1.96 g, 98%)
1-((Z)-2-(pyridin-3-yl)vinyl)-2-((Z)-2-(pyridin-3-yl)vinyl)benzene (Z,Z-2) as white powder:
mp 76 – 78 °C; Rf (PE/EtOH 9.5:0.5) = 0.72; UV (EtOH) λmax/nm (ε/dm3 cm-1mol-1): 253
(8125), 280 (8561); UV (n-hexane) λmax/nm (ε/dm3 cm-1mol-1): 270 (7591); IR νmax/cm-1
1
(NaCl): 2091, 1641, 1397; H NMR (CDCl3, 600 MHz) δ/ppm: 8.38 (s, 2H, H-Py1), 8.35 (d,
Jpy2 = 5.6 Hz, 2H, H-Py2), 7.35 (d, Jpy4 = 7.9 Hz, 2H, H-Py4), 7.21 – 7.18 (m, 2H, H-Ar1/Ar2),

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7.14 – 7.12 (m, 2H, H-Ar1/Ar2), 7.07 – 7.05 (m, 2H, H-Py3), 6.73 (d, JEt1 = 12.1 Hz, 2H, H-
13
Et1), 6.54 (d, JEt2 = 12.1 Hz, 2H, H-Et2); C NMR (CDCl3, 150 MHz) δ/ppm: 149.7 (d, C-
Py1), 147.6 (d, C-Py2), 135.2 (s), 134.9 (d, C-Py4), 132.1 (s), 130.7 (d, C-Et1), 128.9 (d, C-
Ar1/2), 127.3 (d, C-Ar1/2), 126.9 (d, C-Et2), 122.4 (d, C-Py3); HRMS (MALDI-TOF/TOF)
(m/z) for C20H16N2 (M + H)+ calcd 284.1315 found 284.1313.
1-((Z)-2-(pyridin-3-yl)vinyl)-2-((E)-2-(pyridin-3-yl)vinyl)benzene (Z,E-2) as colorless
powder: mp = 66 – 69 °C; Rf (PE/EtOH 9.5:0.5) = 0.68; UV (EtOH) λmax/nm (ε/dm3 cm-1mol-
1
1): 284 (22925), 310 (21457); UV (n-hexane) λmax/nm (ε/dm3 cm-1mol-1): 272 (17783); H
NMR (CDCl3, 600 MHz) δ/ppm: 8.63 (s, 1H, H-Py1t), 8.46 (d, JPy = 4.7 Hz, 1H, H-Py2t), 8.37
(s, 1H, H-Py1c), 8.32 (d, JPy = 4.7 Hz, 1H, H-Py2c), 7.73 (d, JPy = 7.9 Hz, 1H, H-Py4t), 7.65 (d,
JAr = 7.9 Hz, 1H, H-Ar1), 7.35 – 7.30 (m, 2H, H-Ar2, H-Ar3), 7.32 (d, JEtt1 = 16.6 Hz, H, H-
Ett1) 7.27 – 7.24 (m, 1H, H-Py3t), 7.21 – 7.16 (m, 2H, H-Ar4, H-Py4c), 7.02 – 7.0 (m, 1H, H-
Py3c), 6.95 (d, JEtt2 = 16.4 Hz, 1H, H-Ett2), 6.92 (d, J Etc1 = 12.2 Hz, 1H, H-Etc1 ), 6.69 (d, JEtc2
13
= 12.1 Hz, 1H, H-Etc2); C NMR (CDCl3, 150 MHz) δ/ppm: 149.8 (d, C-Py1b), 148.2 (d, C-
Py2b), 148.0 (d, C-Py1a), 147.6 (d, Py2a), 135.5 (s), 135.1 (d, C-Ar2, C-Ar3), 134.5 (s), 132.5
(s), 132.2 (d, C-Py4a), 131.9 (s), 130.8 (d, C-Etc1), 129.0 (d, C-Py4b), 128.2 (d, C-Ett1), 127.8
(d, C-Etc2), 127.6 (d, C-Ar4), 126.1 (d, C-Ett2), 125.5 (d, C-Ar1), 123.0 (d, C-Py3a), 122.4 (d,
C-Py3b).
1-((E)-2-(pyridin-3-yl)vinyl)-2-((E)-2-(pyridin-3-yl)vinyl)benzene (E,E-2) as colorless
powder: mp = 155 – 161 °C; Rf (PE/EtOH 9.5:0.5) = 0.30; UV (EtOH) λmax/nm (ε/dm3 cm-
1mol-1): 284 (11021), 317 (Sh 9635); UV (n-hexane) λmax/nm (ε/dm3 cm-1mol-1): 275 (9686),
308 (Sh, 8292); 1H NMR (CDCl3, 600 MHz) δ/ppm: 8.74 (s, 2H, H-Py1), 8.52 (d, Jpy2/3 = 4.4
Hz, 2H, H-Py2), 7.86 – 7.84 (m, 2H, H-Py4), 7.62 – 7.61 (m, 2H, H-Ar1), 7.51 (d, JEt1/2 = 16.1
Hz, 2H, H- Et2), 7.36 – 7.35 (m, 2H, H-Ar2), 7.32 – 7.30 (m, 2H, H-Py3), 6.99 (d, JEt1/2 = 16.1
Hz, 2H, H-Et1); 13C NMR (CDCl3, 150 MHz) δ/ppm: 148.3 (d, C-Py1), 148.1 (d, C-Py2),
135.1 (s), 132.5 (s), 132,3 (d, C-Py4), 128.0 (d, C-Et2), 127.8 (d, C-Ar2), 127.5 (d, C-Et1),
126.3 (d, C-Ar1), 123.1 (d, C-Py3).
1,2-bis(2-(pyridin-4-yl)vinyl)benzene (3) (1.48 g, 74%)

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1-((Z)-2-(pyridin-4-yl)vinyl)-2-((Z)-2-(pyridin-4-yl)vinyl)benzene (Z,Z-3) as colorless
powder: mp = 154-160 °C; Rf (PE/EtOH 9.5:0.5) = 0.54; IR νmax/cm-1 (NaCl): 1695, 1416,
1327; UV (EtOH) λmax/nm (ε/dm3 cm-1mol-1): 264 (2506), 270 (2634), 280 (2819), 314 (Sh
1
2235); UV (n-hexane) λmax/nm (ε/dm3 cm-1mol-1): 264 (2743), 307 (Sh 1750); H NMR
(CDCl3, 600 MHz) δ/ppm: 8.40 (d, JPy1/2 = 5.5 Hz, 2H, H-Py1), 7.19 – 7.14 (m, 2H, H-Ar1, H-
Ar2), 6.96 (d, JPy2/3 = 5.5, 2H, H-Py2), 6.78 (d, JEt1/2 = 12.1 Hz, 1H, H-Et2), 6.50 (d, JEt1/2
=
13
12.1 Hz, 1H, H-Et1); C NMR (CDCl3, 150 MHz) δ/ppm: 149.3 (d, C-Py1), 143.8 (s), 134.9
(s), 132.4 (d, C-Et2), 128.9 (d, C-Ar1/Ar2), 128.3 (d, C-Et1), 127.5 (d, C-Ar1/Ar2), 122.8 (d, C-
Py2), HRMS (MALDI-TOF/TOF) (m/z) for C20H16N2 (M + H)+ calcd 284.1317 found
284.1313.
1-((Z)-2-(pyridin-4-yl)vinyl)-2-((E)-2-(pyridin-4-yl)vinyl)benzene (Z,E-3) as colorless
powder: mp = 172-175°C; Rf (PE/EtOH 9.5:0.5) = 0.53; UV (EtOH)) λmax/nm (ε/dm3 cm-1mol-
1): 290 (19314), 310 (18362); UV (n-hexane) λmax/nm (ε/dm3 cm-1mol-1): 280 (13764), 307
1
(12313); H NMR (CDCl3, 600 MHz)
δ
/ppm: 8.56 (d, JPy1/Py4 = 5.5 Hz, 2H, H-Py1), 8.36 (d,
JPy1/Py4 = 5.5 Hz, 2H, H-Py4), 7.67 (d, JAr1/Ar4 = 7.7, 1H, H-Ar1), 7.44 (d, JEt,t1/Et,t2 = 16.2 Hz,
1H, H-Et2), 7.35 (dd, JAr2/Ar3 = 15.1, 1H, H-Ar2), 7.28 (d, JPy2/Py3 = 5.5, 2H, H-Py2), 7.23 (dd,
JAr2/Ar3 = 15.1, 1H, H-Ar3), 7.16 (d, JAr1/Ar4 = 7.7, 1H, H-Ar4), 7.00 (d, JEtc1/Etc2 = 12.1, 1H, H-
Etc2), 6.94 (d, JPy2/Py3 = 5.5, 1H, H-Py3), 6.89 (d, JEt1/Et2 = 16.2, 1H, H-Ett1), 6.68 (d, JEt,c1/Et,c2
= 12.1, 1H, H-Etc1); 13C NMR (CDCl3, 150 MHz) δ/ppm: 149.4 (d, C-Py1), 149.0 (d, C-Py4),
144.4 (s), 143.8 (s), 135.8 (s), 134.1 (s), 132.7 (d, C-Ett2), 130.4 (d, C-Ett1), 129.1 (d, C-Etc2),
128.9 (d, C-Etc1), 128.1 (d, C-Ar3), 127.8 (d, C-Ar2), 127.2 (d, C-Ar4), 125.7 (d, C-Ar1), 122.8
(d, C-Py3), 120.4 (d, C-Py2).

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1-((E)-2-(pyridin-4-yl)vinyl)-2-((E)-2-(pyridin-4-yl)vinyl)benzene (E,E-3) as yellow
powder: mp 120 °C – 125 °C: Rf (PE/EtOH 9.5:0,5) = 0.48; UV (EtOH) λmax/nm (ε/dm3 cm-
1mol-1): 287 (29077), 322 (21299); UV (n-hexane) λmax/nm (ε/dm3 cm-1mol-1): 221 (12469),
280 (16032), 310 (14484); 1H NMR (CDCl3, 600 MHz) δ/ppm: 1H NMR (CDCl3, 600 MHz)
δ
/ppm: 8.61 (d, JPy1/2 = 6.2 Hz, 2H, H-Py1), 7.64 (d, JEt1/2 = 16.3 Hz, 1H, H-Et1), 7.63-7.61 (m,
1H, H-Ar1), 7.39-7.37 (m, 3H, H-Py2, Ar2), 6.93 (d, JEt1/2 = 16.3, 1H, H-Et2); 13C NMR
(CDCl3, 150 MHz) δ/ppm: 149.8 (d, C-Py1), 143.9 (s), 134.8 (s), 130.1 (d, C-Ar1), 128.9 (d,
C-Et2), 128.3 (d, C-Ar2), 126.7 (d, C-Et1), 120.5 (d, C-Py2).
2.3. Photochemical and photophysical experiments
2.3.1. Photochemical preparative experiments in intramolecular conditions
86 mg of mixture of isomers of compounds 1-3 was dissolved in 100 mL (c = 3 x 10-3 mol/L)
of toluene and transferred to a quartz vessel. Vessels were purged with argon (99.99%) for 20
minutes and irradiated with 16 UV lamps at 300 nm for 3 h, 7 h, 24 h and 48 h, respectively.
After removal of the solvent (450C, 50-100 atm), 1H NMR spectra showed no reaction, except
isomerization, in shorter period of time, and only high molecular weight products at
prolonged irradiation time (24 and 48 h).
2.3.2. Photochemical preparative experiments in intramolecular conditions with iodine
100 mg of mixture of isomers of compounds 1-3 was dissolved in 120 mL (c = 3 x 10-3
mol/L) of toluene and trace amounts of iodine (1-2 mg) and transferred to a quartz vessel.
These solutions were irradiated with 16 UV lamps at 300 nm for 3 h, 5 h and 24 h,
1
respectively. After removal of the solvent, H NMR spectra showed only high molecular
weight products.
2.3.3. Photochemical preparative experiments in intermolecular conditions
86 mg of mixture of isomers of compounds 1-3 was dissolved in 1 mL (c = 3 x 10-1 mol/L) of
toluene and transferred to a quartz vessel. Vessels were purged with argon for 20 minutes and
irradiated with 16 UV lamps at 300 nm for 7 h and 24 h respectively. After removal of the
solvent, 1H NMR spectra showed no reaction, except isomerization, in shorter period of time,
and with high molecular weight products at prolonged irradiation times (24 and 48 h) trace
amounts (< 2 mg, 2%) of dimeric product 5 were present.
,
,
,
2-[(2R,3S,4R,5S,12R,13S,14R,15S)-4,13,14-tris(pyridin-2-yl)pentacyclo[14.4.0.0² .0 ¹¹.0¹² ¹ ]
1
icosa-1(16),6(11),7,9,17,19-hexaen-3-yl]pyridine (5) (trace amounts, < 2 mg, 2%) as oil: H
NMR (CDCl3, 600 MHz) δ/ppm: 8.47 (d, 1H, JPy1/2 = 5.3 Hz, H-Py1), 7.40 (dd, JPy2/3 =7.3 Hz,
JPy3/4 = 7.8 Hz, 1H, H-Py3), 7.05-7.03 (m, 1H, H-Ar), 6.97 (d, J1/2= 5.3 Hz, JPy2/3 =7.3 Hz, 1H,
H-Py2), 5.12 (d, 2H, JA/B = 5.8 Hz, H-A), 4.76 (d, 1H, JA/B = 5.8 Hz, H-B); 13C NMR (CDCl3,

ACCEPTED MANUSCRIPT
150 MHz) δ/ppm: 159.9 (s), 148.4 (d, Py1), 138.7 (s), 135.1 (d, Py3), 125.6 (d, Py4), 124.6 (d,
Ar), 122.8 (d, C-Ar), 120.4 (d, C-Py2), 46.3 (d, C-B), 43.6 (d, C-A).
2.3.4. Photophysical experiments
The irradiations were carried out with 3 mL of solutions (3 x 10-5 and 3 x 10-6 mol/L) in UV
cuvettes that are 1 cm in width. Experiments were conducted at room temperature. As
solvents commercial 96% ethanol and n-hexane p.a. were used. During the photolysis the
reaction mixtures were stirred by a magnetic stirrer. For photochemical reactions under
continuous irradiation at 300 nm Luzchem photochemical reactor was used equipped with 16
lamps. Incident light intensity was determined using the ferrioxalate actinometer [30, 36, 37].
Following the change of the absorption spectrum of the solution photolyzed, the quantum
yield for the photochemical transformations of the starting material was determined from the
initial rate calculated from the absorbance vs time plot at a characteristic wavelength.
Emission spectra were measured on a Cary Eclipse spectrofluorimeter. Quinine bisulphate
[38, 39] (in 0.5 mol/L H2SO4) was utilized as reference for determination of the fluorescence
quantum yields. Each isomer of the compounds 1-3 was excited at the wavelength of its
absorption maximum.
2.4. X-ray analysis of the 1-((E)-2-(pyridin-4-yl)vinyl)-2-((E)-2-(pyridin-4-yl)vinyl)benzene
(Z,Z-3)
Suitable crystals of compound Z,Z-3 were grown at room temperature from a solution of
ethanol and diethyl ether.
Data collections were performed on an Enraf Nonius CAD4 diffractometer, using graphite
monochromated MoKα (0.71073 Å) radiation at room temperature [293(2) K]. The WinGX
standard procedure was applied for data reduction [41]. Three standard reflections were
measured every 120 minutes as intensity control. No absorption correction was applied.
The structure was solved with SHELXS97 [42] and refined with SHELXL2014 [43]. Models
were refined using the full matrix least squares refinement. Hydrogen atoms bound to C atoms
were refined as riding entities and those bound to O were located in difference Fourier maps
and refined with the following restraints: O-H distance 0.95(2) Å and intramolecular H…H
distance 1.50(4) Å. The atomic scattering factors were those included in SHELXL2014 [43]
Molecular geometry calculations were performed with PLATON, [44] and the molecular
graphics were prepared using ORTEP-3 [45] and CCDC-Mercury [46] Crystallographic and
structure refinement data are shown in table 1 (see also supporting info 2).
Table 1. Crystallographic and structure refinement data.
Compound
Z,Z-3

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Empirical formula
C21H19Ca0.50N2O3
383.42
Formula wt. / g mol-1
Crystal dimensions / mm
Space group
a / Å
b / Å
c / Å
0.40 x 0.30 x 0.25
P 1
ꢀ
6.598(2)
11.712(3)
12.649(3)
100.76(2)
91.34(3)
89.77(3)
2
959.9(5)
1.327
0.222
α / °
β / °
γ / °
Z
V / Å3
Dcalc / g cm-3
µ
/ mm-1
Θ range / °
T(K)
8.00 – 14.27
293(2)
Radiation wavelength
Diffractometer type
0.71073 (MoKα)
Enraf Nonius CAD4
-7 > h > 7;
-13 > k > 13;
15 > l > 0
3875
Range of h, k, l
Reflections collected
Independent reflections
Observed reflections
(I ≥ 2σ)
3349
2421
Rint
0.0666
0.0571
0.1706
R (F)
Rw (F2)
No. of parameters, restraints 280, 5
Goodness of fit
1.059
0.297; – -0.424
∆
ρ
max , ∆
ρ
min (eÅ–3)
3. Results and discussion
Compounds 1,2-di-(2/3/4)-pyridylbenzenes 1-3 that were synthesized by Wittig reactions
were purified and isomers were separated and completely spectroscopically characterized (see
section 2.2. and supporting info 1). For the compound Z,Z-3 X-ray structure was determined
(see section 2.4. and supporting info 2). In the formation of the crystals the molecules
coordinated around a calcium atom (figure 3).
Figure 3. Molecular structure of compound Z,Z-3. Displacement ellipsoids are drawn for the
probability of 30% and hydrogen atoms are shown as spheres of arbitrary radii.

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The molecular symmetry of Z,Z-3 is Ci, with the calcium atom located on a center of
ꢀ
inversion in the space group P1. Two oxygen atoms of hydrogen carbonate are disordered
over two positions (designated as O1,O1A and O2,O2A) with respective populations of 0.54
and 0.46. Crystal packing of Z,Z-3 is realised by hydrogen bonded layers parallel to the plane
...
ꢀ
(011), which are generated by a single N-H O hydrogen bond (figure 4).
0
b
c
Figure 4. Crystal packing of Z,Z-3 showing hydrogen bonding N-H...O, viewed in the
direction [100].
Compound Z,Z-3 crystalized in one of the probable forms but without further calculations the
most energetically stable conformation cannot be exactly established. Some of these
photophysical calculations could give further insight into calculated ground and excited state
dipole moments, total energies, relative abundances and main configuration and oscillator
strengths of electronic transitions of the different rotamers.
3.1. Photochemical experiments
Following the logic of the previously synthesized and studied stilbene [29] and butadiene [30]
heterocyclic compounds (section 1) photochemical experiments were done in the conditions
for intramolecular (c = 3 x 10-3 mol/L) cycloaddition reactions to take place. These
irradiations were conducted in argon purged toluene solutions as was described in the section
1
2.3.1. After removal of the solvent H NMR spectra were recorded. Unlike all the previously
studied furyl- and thienyl-derivatives that in these conditions gave the polycyclic products in
this case only cis-trans (E-Z) isomerization and subsequent polymerization to high molecular
weight products was detected.
The next step was to try the irradiation experiments in solutions that were not purged with
argon (there is dissolved oxygen present in the solution) and with the addition of iodine.

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These experiments proved that there are no products of electrocyclization that would form, as
the 1H NMR spectra showed only high molecular weight products in all of the cases.
When the conditions were modified to enhance the chances for the intermolecular
cycloaddition reaction (c = 3 x 10-1 mol/L) to take place (dimerization) only after the
irradiation of the 1,2-bis(2-(pyridin-2-yl)vinyl)benzene (1) small amounts of the dimeric
cycloadduct 5 (scheme 4) were isolated and characterized.
Scheme 4. Excited state reactions of compound 1 in toluene at 300 nm.
In the intermolecular cycloaddition process theoretically different dimers could have been
1
formed but the H NMR spectra of the product 5 is quite simple (see supporting info 1) and
this can only be the case if the dimer that formed has 2 symmetry planes (scheme 4). The
structure
of
the
2-[(2R,3S,4R,5S,12R,13S,14R,15S)-4,13,14-tris(pyridin-
,
,
,
2yl)pentacyclo[14.4.0.0² .0 ¹¹.0¹² ¹ ]icosa-1(16),6(11),7,9,17,19-hexaen-3-yl]pyridine (5)
was confirmed additionally by 2D NMR spectroscopy.
To try to explain the general photochemical non-reactivity of the compounds 1-3 research was
broadened. Irradiation experiments were conducted in UV cuvettes and the progress was
monitored by UV/Vis spectrophotometry. The irradiations were carried out both in ethanol
and n-hexane to study the effect of the polarity of the solvent on the general excited state
behavior. All of the cuvettes were purged with argon to completely rule out any possibility of
a photo-induced oxidation reactions in the excited state. The concentration of the starting
compounds was 3 x 10-5 mol/L. The photolyses were conducted using 300 nm lamps in the
Luzchem photochemical reactor equipped with a stirrer. Comparison of the photolysis spectra
for the E,E-isomers of compounds 1-3 in both n-hexane and ethanol are given on figures 5-7.

ACCEPTED MANUSCRIPT
1,6
1,4
1,2
1,0
0,8
0,6
0,4
0,2
0,0
3,0
ethanol
n
-hexane
0 s
1 s
2 s
4 s
8 s
16 s
32 s
64 s
128 s
256 s
512 s
1024 s
2028 s
2,5
0 s
1 s
2 s
4 s
2,0
A
8 s
1,5
A
16 s
32 s
64 s
128 s
256 s
512 s
1024 s
1,0
0,5
0,0
200
250
300
350
400
450
200
300
400
λ
/ nm
λ
/ nm
Figure 5. Spectral changes during the irradiation of E,E-1 in 96% ethanol and n-hexane (λirr
300 nm, l = 1 cm).
=
=
=
0,30
0,5
ethanol
n
-hexane
0,25
0,20
0,15
0,10
0,05
0,00
0 s
1 s
2 s
4 s
0 s
1 s
2 s
4 s
0,4
0,3
0,2
0,1
0,0
8 s
8 s
A
A
16 s
32 s
64 s
128 s
256 s
512 s
1024 s
16 s
32 s
64 s
128 s
256 s
512 s
1024 s
200
250
300
350
400
200
250
300
350
400
λ
/ nm
λ
/ nm
Figure 6. Spectral changes during the irradiation of E,E-2 in 96% ethanol and n-hexane (λirr
300 nm, l = 1cm).
1,2
1,0
0,8
0,6
0,4
0,2
0,0
0,8
0,6
0,4
0,2
0,0
ethanol
n
-hexane
0 s
1 s
2 s
4 s
8 s
16 s
32 s
64 s
128 s
256 s
512 s
1024 s
0 s
1 s
2 s
4 s
A
A
8 s
16 s
32 s
64 s
128 s
256 s
512 s
200
250
300
350
400
200
300
400
λ
/ nm
λ
/ nm
Figure 7. Spectral changes during the irradiation of E,E-3 in 96% ethanol and n-hexane (λirr
300 nm, l = 1cm).
Maximum time of irradiation was kept from 512 to 2048 s. It can be seen from these
measurements that the compounds E,E-1-3 react as fast in ethanol as in n-hexane. There is a
simultaneous drop in absorbance and a significant hypsochromic shift that is taking place in
both solvents (figure 5-7). This indicates that E–Z, that is, trans–cis isomerization takes place

ACCEPTED MANUSCRIPT
at shorter irradiation times (under 10 s). The composition of the photostationary mixture
would be very hard to determine, because there is the possibility of existence and
interconversion between three geometrical isomers: E,E, E,Z and Z,Z, respectively. The
significant drop in the maxima (after approx. 128 s) is caused by formation of products with
reduced or no conjugation present in the molecule. Meaning that the long-range conjugation
between the two pyridyl-groups via the hexatriene link ceases to exist and this chromophore
system is slowly extinguished. Quantum yields were measured for these photo-induced
disappearances of the starting molecules in both of the solvents used and they are summarized
in Table 2.
Table 2. Quantum yields for the photolysis of di-(2/3/4)-pyridine-stilbene derivatives 1-3 in
argon flushed n-hexane and ethanol (λirr = 300 nm)a,b
Compound
Φ
(n-hexane)
0.43
Φ (ethanol)
Z,E-2 Py (Z,E-1)
E,E-2 Py (E,E-1)
Z,Z-3 Py (Z,Z-2)
Z,E-3 Py (Z,E-2)
E,E-3 Py (E,E-2)
Z,Z-4 Py (Z,Z-3)
Z,E-4 Py (Z,E-3)
E,E-4 Py (E,E-3)
0.48
0.39
0.52
0.64
0.42
0.46
0.45
0.45
0.11
0.27
0.31
0.50
0.16
0.59
0.34
a
Calculation report can be found in the Supporting information file 1;
b Standard deviation: ±7%
The initial drop in absorbance is faster in ethanol than in n-hexane, for the E,E-1, and vice
versa in the case of E,E-2 (figure 5,6). This indicates that there is a strong solvent effect
present in the case of the E,E-1, that is the 2-pyridine derivative. This is corroborated with
quantum yields, where the quantum yield of the E,E-1 in n-hexane is four time lower than in
ethanol (table 2). This is true for three compounds, E,E-1, Z,Z-2 and Z,Z-3. This phenomenon
indicates that the transition state of the reaction reached upon excitation is more polar than the
initial (ground) state. An increase in the polarity of the solvent will thus stabilize the transition
state, when compared to the ground state, and lead to an increase in the reaction rate, here
measured via the quantum yield [40]. For the compounds E,E-2 and Z,E-3 the quantum yield
is slightly higher in n-hexane than in ethanol thus indicating that the transition state upon
excitation is somewhat less polar than the ground state. This determined that both the position
of nitrogen in the system as well as the configuration of the molecule play a big role in their
photophysical behavior.

ACCEPTED MANUSCRIPT
If we illustrate the relative number of double bonds that can be in conjugation, as is in the
figure 8 on the example of one of the possible resonance structures for all derivatives 1-3,
then it is visible that this number varies depending on the placement of the nitrogen in the
skeleton.
Figure 8. Prolonged conjugation of double bonds.
In the compounds 2 and 3 there are 7 double bonds that can be included in the prolonged
conjugation and in the compound 1 there is a maximum of 9 double bonds. It is also important
to keep in mind that the E,E-isomers are completely planar and this to facilitates better
delocalization of π-electrons reducing the energy barrier and thus by rule shifting E-isomers to
shorter wavelength when compared to Z-isomers. If we compare the photolysis quantum
yields between isomers of the same compounds then it can be noted that in the case of the di-
2-pyridine-stilbene 1 and di-3-pyridine-stilbene 2 the largest quantum yield is that of the E,Z-
isomer. In the case of the di-4-pyridine-stilbene 3 the photolysis quantum yields for all of the
three isomers are very similar. As was mentioned (section 2.2.), in earlier papers [32-34] that
were comparing the di-4-pyridine-stilbene to other hetero-analogues of 1,2-distyrylbenzene an
exhaustive description of this compound was given, among other details it covered quantum
yield of fluorescence (ΦF = 0.026), quantum yield of isomerization (ΦEE ZE = 0.30) as well as
ꢀ
lifetimes given for the solutions of the compound in methyl-cyclohexane/3-methylpentane
(MCH/3MP).
3.2. Photophysical experiments and calculations
3.2.1. UV-Vis absorption spectra
The comparison of the absorption and emission spectra for the E,E-isomers of compounds 1-3
is given on figure 9 and for the Z,Z- and Z,E-isomers of compounds 1-3 in ethanol and n-
hexane see supporting information file 1.

ACCEPTED MANUSCRIPT
5
4
3
2
1
0
5
ethanol
n
-hexane
4
E,E-1 abs
E,E-1
E,E-2 abs
E,E-2
E,E-3 abs
E,E-
E,E-1 abs
E,E-1
E,E-2 abs
E,E-2
E,E-3 abs
E,E-3
3
3
2
1
0
ε
ε
250
300
350
400
450
500
550
600
250
300
350
400
450
/ nm
500
550
600
λ
/ nm
λ
Figure 9. Absorption and normalized emission spectra for the E,E-1-3 in ethanol and n-
hexane.
It is visible that the 2-pyridine derivative 1 has a hyperchromic shift when compared to the 3-
and the 4-pyridine derivatives (figure 9) and this would be in concordance with the prolonged
conjugation caused by nitrogen placement (figure 8). What is very interesting to note is that in
both ethanol and n-hexane solutions the E,E-2 isomer, that is the 1-((E)-2-(pyridin-3-
yl)vinyl)-2-((E)-2-(pyridin-3-yl)vinyl)benzene, has the lowest absorption of the three
compounds. The emission spectra of the E,E-1-3 have a considerable shift to higher
wavelengths and they cannot be considered mirror images (figure 10 and supporting
information file 1).
5
absorption (etoh)
emmision (etoh)
absorption ( -hexane)
-hexane)
4
3
2
1
0
n
n
emmision (
A
N
N
S0ꢀS1
E,E-1
S1ꢀS0
200
250
300
350
400
450
500
550
λ
/ nm
Figure 10. Absorption and normalized emission spectra for the E,E-1 in ethanol and n-
hexane.
There is uniformity present in all of the spectra when absorption and emission is compared.
On the example of E,E-1 in ethanol and n-hexane (figure 10) we can see that the fluorescence

ACCEPTED MANUSCRIPT
emission occurs from the lowest excited state (S1), resulting in a spectrum that mirrors the
ground to first excited state transition and almost no spectral shift is observable between two
solvents (figure 10).
To summarize the characteristic absorption and emission spectral data tables 3 and 4 are
given. They also contain the calculations of the vibronic progression of the absorption spectra
(∆νabs, where available) as well as Stokes shifts (∆νs,,max) of the compounds 1-3 in ethanol and
n-hexane, respectively.
Table 3. Spectral behavior of the di-(2/3/4)-pyridine-stilbene derivatives 1-3 in ethanol at
room temperature
λ
max /nm (log ε)
∆
ν
abs / cm-1
λ
F,max / nm
430
∆
ν
S,max / cm-1
9002
compound
Z,E-1
E,E-1
Z,Z-2
Z,E-2
E,E-2
Z,Z-3
Z,E-3
E,E-3
262, 270, 310 (3.96)
227, 237, 275, 312 (4.66)
253, 280 (3.93)
-
-
374
5313
-
415
11618
8277
284 (4.36), 310
2953
3665
6032
-
417
284 (4.04), 317
414
7391
264 (3.99), 270, 280, 314
290 (3.45), 310
414
7693
415
8162
287 (4.46), 322
3787
415
6960
Table 4. Spectral behavior of the di-(2/3/4)-pyridine-stilbene derivatives 1-3 in n-hexane at
room temperature
λ
max /nm (log ε)
∆
ν
abs / cm-1
910
-
λ
F,max / nm
408
∆
ν
S,max / cm-1
6838
compound
Z,E-1
E,E-1
Z,Z-2
Z,E-2
E,E-2
Z,Z-3
Z,E-3
E,E-3
237, 310 (4.02), 319
275, 309 (4.54)
270 (3.88)
375
5696
-
410
12647
12493
8254
272 (4.25)
-
412
275 (3.99), 308
264 (3.44), 307
280 (4.14), 307
221, 280 (4.20), 310
3896
5305
3141
3456
413
403
7759
408
8063
406
7628
Both of the isomers of the compound 1 have band absorption maxima around 310 nm thus
having a bathochromic shift when compared to the derivatives 2 and 3. There doesn’t seem to
be a difference in the non-polar n-hexane, other than the lower absorption coefficient in all of
the compounds (figure 9, section 2.2.)

ACCEPTED MANUSCRIPT
The vibronic progression of absorption was calculated for compounds 2 and 3 and it was in
the range from 2953 to 6032 cm-1. This electronic excitation probably causes a significant
change in the molecular geometry as indicated by the very large Stokes shifts.
3.2.2. Fluorescence quantum yield
As the comparison of the emission and the absorption spectra (figures 9, 10) of the studied
compounds revealed interesting features of the system the next step was to record and
calculate the quantum yields of fluorescence in both of the solvents (table 5).
Table 5. Quantum yields of fluorescence for the di-(2/3/4)-pyridine-stilbenes 1-3
compound
Z,E-1
Φ
F (n-hexane)
0.10
Φ
F (ethanol)
0.18
Σ
Φ
(n-hexane)
0.53
Σ
Φ
(ethanol)
0.65
E,E-1
Z,Z-2
0.55
0.26
0.66
0.66
0.07
0.38
0.34
0.90
Z,E-2
0.64
0.44
0.96
1.08
E,E-2
Z,Z-3
0.43
0.58
0.94
1.00
0.12
0.11
0.28
0.57
Z,E-3
0.31
0.64
0.90
1.09
E,E-3
0.32
0.16
0.66
0.61
The fluorimetric quantum yields in ethanol, for most of the compounds studied, are higher
than the ones in n-hexane. Exceptions are the E,E-1 and Z,E-2 and this corresponds perfectly
with the higher quantum yields of photolysis that these compounds have in ethanol, indicating
that the efficient stabilization of the polar excited state increases the probability of the
photochemical conversion in competition with the emission.
The sum of the photolysis and the fluorescence quantum yields is one only in the case of the
Z,E-2, E,E-2 and Z,E-3 meaning that in this three cases these are probably the only two routes
of decay and they use up the total energy of the excited state. All of the other compounds have
additional ways by which they lose energy and come back into the ground state. We have
shown that a small amount of intermolecular cycloaddition product 5 is formed in the case of
the compound 1 indicating that a portion of energy in this case is used up for this reaction to
take place. Other possible paths could include, like in the case of the previously studied
benzofuran derivatives, an intersystem crossing (S1ꢀT1) leading to the non-reactive triplet
state [18,19]. Considering that the analyzed compounds 1-3 possess a nitrogen atoms in the
structure, that can influence the fluorimetric quantum yields by lowering their values

ACCEPTED MANUSCRIPT
especially in the cases of those geometrical isomers where the (n,π*) nature of the S1 excited
state becomes a dominant one.
4. Conclusion
Stilbene analogues, di-(pyridin-2/3/4-yl)vinyl)benzenes 1-3, including the new and previously
undescribed di-(pyridin-2/3-yl)vinyl)benzenes 1-2, were synthesized and completely
spectroscopically and photophysically characterized. Upon irradiation di-(pyridin-3/4-
yl)vinyl)benzenes showed no other process but isomerization in conditions for both intra- and
intermolecular reactions. Di-(pyridin-2-yl)vinyl)benzene
1
gave by intermolecular
cycloaddition reaction, in trace amounts, a dimeric cyclophane product (5). General
photochemical unreactivity towards electrocyclization and cycloaddition reactions led to
further investigations and description of some photophysical properties. Quantum yields of
photolysis as well as fluorescence were measured and calculated, their sum was one for only
the Z,E-2, E,E-2 and Z,E-3. Other compounds have additional routes of losing excited state
energy. We have shown that the placement of the nitrogen in the system plays an important
role in the photophysical properties. The difference of the photophysical properties in relation
to the configurational isomers was also determined as well as the impact of the polarity of the
solvent on the system. It was shown both by the photolysis and fluorescence quantum yields
comparison in ethanol vs n-hexane that the excited state of the compounds E,E-1 and Z,E-2 is
polar and thus stabilized in ethanol. In general, the results show that the polarity effect of the
medium has a complex influence on the photobehaviour and that the measured effects are
probably not coming only from polarity.
5.
Supporting Information
1
13
Supporting information file 1 consists of all of the H, C as well as 2D spectra (where they
were recorded) with all of the accompanying data about the solvents and peak assignations. It
also contains absorption and emission spectra. Supporting information file 2 consist of data
for the determined X-ray structure Supplementary crystallographic data for this paper also can
be obtained free of charge via www.ccdc.cam.ac.uk/conts/retrieving.html (or from the
Cambridge Crystallographic Data Centre, 12, Union Road, Cambridge CB2 1EZ, UK; fax:
+44 1223 336033; or deposit@ccdc.cam.ac.uk). CCDC-1821955 contains the supplementary
crystallographic data for this paper.

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6.
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Synthesis, spectroscopic characterization and photophysical investigations
of new di-(2/3)-pyridine-stilbenes; isomerism, nitrogen position influence
and solvent effects
Ivana Šagud[a], Valentina Milašinović[b], Krešimir Molčanov[b], Željko Marinić[c] and Irena Škorić *[a]
aDepartment of Organic Chemistry, Faculty of Chemical Engineering and Technology, University of Zagreb,
Marulićev trg 19, 10000 Zagreb, Croatia, bDepartment for Physical Chemistry, Rudjer Boškovic Institute, Bijenicka
54, 10000 Zagreb, Croatia, cNMR Center, Rudjer Bošković Institute, Bijenička cesta 54, 10000 Zagreb, Croatia
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Stilbene-type analogues with the pyridine ring
Di-(pyridin-3/4-yl)vinyl)benzenes, no other process but isomerization
Di-(pyridin-2-yl)vinyl)benzene, trace amounts of dimeric product
Investigations and description of photophysical properties
Quantum yields of photolysis
Quantum yields of fluorescence