Synthesis and photophysical characterization of novel π-conjugated vinyl sulfides

Article abstract of DOI:10.1016/j.jphotochem.2014.06.003

The synthesis and photophysical properties of a series of π-conjugated vinyl sulfides are described. These compounds exhibited their absorption maxima in the range of 350-366 nm, while the emission spectra displayed peaks in the zone of 421-441 nm; both o

Full text of DOI:10.1016/j.jphotochem.2014.06.003

Journal of Photochemistry and Photobiology A: Chemistry 290 (2014) 1–10
Contents lists available at ScienceDirect
Journal of Photochemistry and Photobiology A:
Chemistry
journal homepage: www.elsevier.com/locate/jphotochem
Synthesis and photophysical characterization of novel ␲-conjugated
vinyl sulfides
Mariana M. Bassacoa, Matias Monc¸ alvesa, Francieli Rinaldia, Teodoro S. Kaufmanb,
Claudio C. Silveiraa,∗
a Departamento de Química, Universidade Federal de Santa Maria, UFSM, 97105-900 Santa Maria, R.S., Brazil
b Instituto de Química Rosario (IQUIR, CONICET-UNR), Suipacha 531, S2002LRK Rosario, Argentina
a r t i c l e i n f o
a b s t r a c t
Article history:
The synthesis and photophysical properties of a series of ␲-conjugated vinyl sulfides are described. These
compounds exhibited their absorption maxima in the range of 350–366 nm, while the emission spectra
displayed peaks in the zone of 421–441 nm; both of them were influenced, although in different degrees,
by the extent of the conjugated system. Red-shifted absorption and emission were observed when the
␲-conjugation was extended, clearly indicating that the sulfur atom participates as a bridge within these
highly conjugated structures. Therefore, this preliminary investigation suggests that vinyl sulfide-based
␲-conjugated materials are promising compounds for the development of novel and efficient organic
emitters.
Received 27 March 2014
Received in revised form 2 June 2014
Accepted 4 June 2014
Available online 12 June 2014
Keywords:
Vinyl sulfides
Wittig–Horner reaction
Fluorescence
© 2014 Elsevier B.V. All rights reserved.
␲-Conjugated system
1. Introduction
most relevant common feature (Fig. 1). In many of these com-
pounds, the ␲-conjugated system embodies a sulfur derivative,
Luminescent compounds are attracting considerable attention
in the fields of biochemistry and materials science [1]. The develop-
ment of polyconjugated fluorescent organic compounds has been
extensively investigated in recent years due to their variety of
optical, electrical and photoelectric properties, and their potential
applications in organic optoelectronics, molecular electronics and
manufacturing of organic light-emitting devices (OLEDs).
The OLEDs are a class of highly advanced electronic devices
which have great quantum efficiencies and are now being com-
mercially available in handheld apparatus and all-size full-color
displays, where they act as successful replacements of the old
cathode ray tubes and the most modern liquid crystal displays
[2]. Therefore, new photoactive materials are continually being
developed for application in high-efficiency organic devices and
the development of simple synthetic routes to wavelength-tunable
fluorophores, with potentialapplicationsin electronicand photonic
devices, is of great interest [3].
mainly thiophene-based (A–E) [4], but heterocycles such as ben-
zothiadiazoles (E) [5], benzothiazoles (F) [6] and others [7] have
also been described.
The frequent use of these heterocycles as ␲-bridges for design
of efficient conjugated structures stems from their excellent optical
and electronic properties, as well as thermal and environmen-
tal stabilities, intrinsic electron-rich nature, and ability to furnish
derivatives under relatively simple conditions [8].
Opposite to the ubiquity of sulfur-containing heterocycles, the
presence of non-heterocyclic sulfur atoms in organic emitters has
been essentially limited. They were placed as linkers [9] between
aromatic structures (G–M), such as in the pyrene derivatives PyG0
(H) and (I), a precursor of visual chemosensors for peroxides [10],
and in the substituted anthracene ANS (J). Alternatively, thioester
[11] or disulfide (K) [12] moieties have been used as peripheral
structural elements to connect molecular wires or just to anchor
various probes to gold particles.
So far, the fluorophores that have demonstrated suitability in
this area have a large and effective ␲-conjugated system, as the
It has been demonstrated that the incorporation of sulfur to
the anthracene core drastically changes the photo- and electronic
properties of the resulting molecules, suggesting that the lone pair
of electrons of sulfur participate in the photo-induced electron
transfer to the excited state of the aromatic tricycle [13]. On the
other hand, Yanai and co-workers [14] synthesized a thioketene
∗
Corresponding author. Tel.: +55 55 32208754.
E-mail address: silveira@quimica.ufsm.br (C.C. Silveira).
http://dx.doi.org/10.1016/j.jphotochem.2014.06.003
1010-6030/© 2014 Elsevier B.V. All rights reserved.

2
M.M. Bassaco et al. / Journal of Photochemistry and Photobiology A: Chemistry 290 (2014) 1–10
C6H13
C10H21
S
S
S
n
S
n
n
A, n= 1,2
m
E
E
S
S
S
n+1
n+1
n
S
S
E
E
n
S
S
S
C10H21
C
m
m
n
n
S
n
n
B, n= 1,2; E= H, Et
C10H21
D, m= 0, n= 2, 3; m= 1, n= 2
S
N
N
R
S
S
S
SiMe3
N
N
R
S
S
n S
n
R
S
S
E
F
S
nS
S
S
n
R
S
R
S
S
N
S
N
N
S
N
n
R
n
S
G, n= 1-3; R= C6H13
OMe
S
S
N
S
S
Me
Me
Me
Me
S
S
S
K
J, ANS
R
R
R
S
S
H, PyG0
I
S
S
S
SO2R2
SR1
N
Ar
Fe
Fe
R
L
M
N, R= H, DPVBi; R= F, DFPVBi
Fig. 1. Chemical structures of some sulfur-containing conjugated heterocycles with potentially useful photophysical and photochemical properties, DPVBi and DFPVBi.
acetal-type dopant (L), and other investigations [15] validated the
use of sulfur as a group electrically equivalent to a double bond for
charge transport in unsaturated chains (M).
synthesis of vinyl chalcogen compounds, we were interested in
the preparation of novel organochalcogen derivatives for potential
applications in optoelectronic devices. Therefore, herein we report
the synthesis, characterization and photoluminiscent properties of
novel ␲-conjugated vinyl sulfides (3), employing aromatic dialde-
hydes (2) as central cores, through the use of a Wittig–Horner based
approach, as shown in Scheme 1.
Furthermore, it has been envisioned that the association of
aromatic rings, sulfur atoms and double bonds in which the delo-
calization of p-electrons through the sulfur bridge is possible,
may endow the resulting molecules with an array of remark-
able characteristics, such as light refractivity and nonlinear optical
properties [16]. These precedents support the hypothesis that non-
heterocyclic organochalcogen moieties can be potentially useful
structural motifs for the design of efficient ␲-systems for organic
electronics.
2. Materials and methods
We have recently reported
a
facile and convenient
2.1. Reagents
Horner–Wittig-based synthetic approach to the preparation
of (diphenylphosphinoyl)methyl vinyl sulfides as well as symmet-
rically and unsymmetrically substituted divinyl sulfides and cyclic
sulfides [17], from the easily available bis[(diphenylphosphinoyl)
methyl]sulfide [18].
The solvents for chemical reactions were purified according to
the literature and transferred under argon, via syringe. The fluores-
cence and UV–vis measurements were carried out in spectroscopic
grade solvents. Commercial reagents were used without further
purification. All the reactions were performed in flame-dried glass-
ware.
Based on the outstanding properties of sulfur-containing deriva-
tives related above, as well as on our previous experience on the

M.M. Bassaco et al. / Journal of Photochemistry and Photobiology A: Chemistry 290 (2014) 1–10
3
1. a. Na, THF
1. TsCl, Et3N, CH2Cl2
2. Na2S, DMF
b. CH2=O
O
P
O
P
O
P
2. H2O2
Ph
Ph
Ph
Ph
Ph
Ph
PPh2
S
S
OH
(78%, overall)
(83%)
R CHO
NaH, THF
up to
70%
O
P
Ph
Ph
S
H
Wittig-Horner
R
+
Ar
OHC
CHO
R
Ar
R
H
S
1
2
3
Scheme 1. Preparation of 1 [17,18] and proposed synthetic strategy toward the vinylic sulfides 3 (Ar = aryl).
2.2. Structural characterization methodology
2.4.2. Synthesis of the 1,4-bis(((methyl)thio)ethenyl)benzenes
3a–g
The melting points were measured on an MQAPF-301 (Micro-
química) instrument and are reported uncorrected. NMR spectra
(1H and 13C) were recorded on Bruker DPX-200 and Bruker
DPX-400 spectrometers (200 and 400 MHz for 1H, respectively).
Chemical shift data are reported in ppm downfield from TMS,
employed as internal standard. Coupling constants (J) are informed
in Hertz. Elemental analyses were recorded on a Perkin-Elmer
CHN 2400 analyzer. Low-resolution mass spectra were run on a
Shimadzu QP2010 Plus CG-MS instrument. High-resolution mass
spectral data were obtained in a Bruker microTOF-Q IIT instru-
ment. Infrared spectra were acquired on a Shimadzu Prestige-21
spectrometer, with the samples prepared as KBr pellets.
A solution of nBuLi in hexanes (4 mmol) was added dropwise
to a stirred solution of the corresponding (diphenylphosphi-
noyl)methyl ethenyl sulfide (1, 2.2 mmol) in THF (15 mL) at room
temperature. After 20 min, terephthalaldehyde (2, 1.0 mmol) was
added and the solution was stirred under reflux for 3–5 h. Then,
saturated aqueous NH4Cl solution (20 mL) was added and the mix-
ture was extracted with EtOAc (2× 20 mL). The organic layer was
dried (MgSO4), filtered and concentrated under reduced pressure.
The residue was purified by column chromatography, eluting with
hexanes.
2.4.2.1. 1,4-bis(2-((Cyclopentylidenemethyl)thio)ethenyl)benzene
(3a). Yield: 74%. Yellow solid, m.p.: 68–72 ◦C. E,E/Z,E: >20/1. IR
(KBr): ꢁ = 2951, 2862, 1589, 1408, 934, 810 and 768 cm−1 1H NMR
.
2.3. Photophysical characterization methodology
(400 MHz, CDCl3): ı = 1.67–1.77 (m, 8 H), 2.30–2.41 (m, 8 H), 5.97
(t, J = 2.2, 2 H), 6.42 (d, J = 15.5, 2 H), 6.73 (d, J = 15.5, 2 H) and 7.20
(s, 4 H). 13C NMR (100 MHz, CDCl3): ı 26.2, 26.7, 31.0, 34.3, 109.4,
124.0, 125.7, 126.1, 136.6 and 150.1. GC–MS: m/z (rel. int., %) = 354
(M+, 98), 229 (66), 199 (11), 197 (14), 191 (12), 185 (11), 173 (17),
161 (18), 147 (49), 129 (28), 125 (100) and 115 (36). Anal. Calcd.
for C22H26S2: C, 74.52; H, 7.39. Found: C, 74.62; H, 8.01.
UV–vis absorption spectra were taken in a Cary 50 Bio UV/Visible
spectrophotometer, employing the pure solvent as reference.
Steady state fluorescence spectra were measured in a Varian Cary
Eclipse fluorescence spectrophotometer. The fluorescence quan-
tum yields (˚F) of the synthesized compounds were determined in
CH2Cl2 solutions (ꢀ2D0 = 1.4242), relative to quinine in 0.1 M H2SO4
(ꢀ2D0 = 1.3576); ˚F = 0.55 at 20 ◦C) [19], employing the follow-
ing equation: ˚Fs = ˚Fr × (Is × ODr × ꢀ2s )/(Ir × ODs × ꢀr2), where I,
OD and ꢀ are the integrated emission intensities of the solutions
(s = sample; r = reference), their corresponding optical densities of
the respective solutions and the refractive index of the solvents
used, respectively. All the experiments were performed at room
temperature with samples in the concentration range of 10−6 to
10−5 M.
2.4.2.2. 1,4-bis(2-((Cyclohexylidenemethyl)thio)ethenyl)benzene
(3b). Yield: 76%. Yellow solid, m.p.: 67–75 ◦C. E,E/Z,E: 4/1. IR (KBr):
ꢁ = 2924, 2851, 1589, 1443, 988, 934, 845 and 775 cm−1 1H NMR
.
(400 MHz, CDCl3): ı (E,E-3b) = 1.51–1.63 (m, 12 H), 2.20–2.35 (m, 8
H), 5.82 (s, 2 H), 6.42 (d, J = 15.4, 2 H), 6.72 (d, J = 15.4, 2 H) and 7.20
(s, 4 H). 13C NMR (100 MHz, CDCl3): ı (E,E-3b) = 26.3, 27.3, 28.2,
30.5, 36.6, 110.9, 124.2, 125.8, 126.2, 135.6 and 147.2. GC–MS: m/z
(rel. int., %) = 382 (M+, 46), 281 (14), 207 (31), 147 (26), 139 (100),
129 (13) and 73 (32). Anal. Calcd. for C24H30S2: C, 75.34; H, 7.90.
Found: C, 74.79; H, 8.07.
2.4. Synthesis
2.4.2.3. 1,4-bis(2-((Cycloheptylidenemethyl)thio)ethenyl)benzene
(3c). Yield: 80%. Yellow solid, m.p.: 60–65 ◦C. E,E/Z,E: 7/1. IR (KBr):
2.4.1. Synthesis of the (diphenylphosphinoyl)methyl ethenyl
sulfides (1a–g)
ꢁ = 2920, 2847, 1586, 1443, 937, 845 and 787 cm−1 1H NMR
.
A stirred solution of bis[(diphenylphosphinoyl)methyl] sulfide
(462 mg, 1 mmol) in THF (10 mL) was treated with NaH (dry
95%; 2 mmol) at room temperature. After 20 min, the appropri-
ate carbonyl compound (1.1 mmol) was added and the system
was stirred for 24 h at 60 ◦C (oil bath temperature). The reac-
tion was quenched with saturated aqueous NH4Cl solution (20 mL)
and the mixture was extracted with CH2Cl2 (3× 20 mL). The com-
bined organic layers were dried (MgSO4), filtered and concentrated
under reduced pressure. The residue was purified by column chro-
matography (CH2Cl2:hexanes:EtOAc, 1:5:4) to give the desired
products.
(400 MHz, CDCl3): ı (E,E-3c) = 1.49–1.69 (m, 16 H), 2.35–2.42 (m,
8 H), 5.89 (s, 2 H), 6.43 (d, J = 15.5, 2 H), 6.73 (d, J = 15.5, 2 H) and
7.20 (s, 4 H). 13C NMR (100 MHz, CDCl3): ı (E,E-3c) = 26.6, 28.9,
29.2, 29.9, 32.2, 37.5, 114.4, 124.0, 125.7, 126.4, 135.6 and 147.4.
GC–MS: m/z (rel. int., %) = 410 (M+, 28), 281 (14), 253 (10), 207
(28), 154 (14), 153 (100), 147 (22), 135 (14) and 117 (13). Anal.
Calcd. for C26H34S2: C, 76.04; H, 8.34. Found: C, 77.21; H, 9.04.
2.4.2.4. 1,4-bis(2-((Cyclooctylidenemethyl)thio)ethenyl)benzene
(3d). Yield: 73%. Yellow solid, mp 52–60 ◦C. E,E/Z,E: 2.5/1. IR
(KBr): ꢁ = 2920, 2847, 1589, 1443, 937, 841 and 787 cm−1 1H NMR
.

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M.M. Bassaco et al. / Journal of Photochemistry and Photobiology A: Chemistry 290 (2014) 1–10
(400 MHz, CDCl3): ı (E,E-3d) = 1.45–1.55 (m, 12H), 1.64–1.72 (m,
8H), 2.30–2.37 (m, 8H), 5.92 (s, 2H), 6.43 (d, J = 15.5, 2H), 6.73
(d, J = 15.5, 2H) and 7.21 (s, 4H). 13C NMR (100 MHz, CDCl3): ı
(E,E-3d) = 25.9, 26.2, 26.3, 26.6, 27.2, 31.1, 37.3, 114.5, 124.1, 125.8,
126.3, 135.6 and 147.9. GC–MS: m/z (rel. int., %) = 438 (M+, 68), 168
(13), 167 (100), 147 (19), 129 (10), 117 (16), 115 (12), 97 (51) and
81 (30). HRMS: found m/z 439.2487; C28H38S2 [(M+H)+] requires
m/z 439.2448.
233 (13), 193 (15), 125 (100), 81 (16) and 79 (32). Anal. Calcd. for
28H30S2: C, 78.09; H, 7.02. Found: C, 78.34; H, 7.58.
C
2.4.3.2. 4,4ꢀ-bis(2-((Cyclohexylidenemethyl)thio)ethenyl)biphenyl
(5b). Yield: 80%. Yellow solid, m.p.: 120–130 ◦C. E,E/Z,E: 10/1. IR
(KBr): ꢁ = 2924, 2847, 1589, 1443, 934, 817 and 783 cm−1 1H NMR
.
(400 MHz, CDCl3): ı (E,E-5b) = 1.57–1.59 (m, 12H), 2.23–2.25 (m,
4H), 2.32–2.35 (m, 4H), 5.84 (s, 2H), 6.48 (d, J = 15.4, 2H), 6.78 (d,
J = 15.4, 2H), 7.34 (d, J = 8.2, 4H) and 7.52 (d, J = 8.2, 4H). 13C NMR
(100 MHz, CDCl3): ı (E,E-5b) = 26.3, 27.2, 28.3, 30.5, 36.6, 110.8,
124.7, 125.9, 125.9, 126.9, 136.0, 138.8 and 147.3. GC–MS: m/z (rel.
int., %) = 458 (M+, 28), 169 (35), 147 (24), 139 (100), 97 (28) and 79
(34). Anal. Calcd. for C30H34S2: C, 78.55; H, 7.47. Found: C, 78.51;
H, 7.49.
2.4.2.5. 1,4-bis(2-(((4-Methylcyclohexylidene)methyl)thio)ethenyl)
benzene (3e). Yield: 86%. Yellow solid, m.p.: 37–55 ◦C. E,E/Z,E: 6/1.
IR (KBr): ꢁ = 2920, 2847, 1589, 1454, 1288, 1227, 937, 837 and
771 cm−1 1H NMR (400 MHz, CDCl3): ı (E,E-3e) = 0.92 (d, J = 6.6,
.
6H), 0.96–1.09 (m, 4H), 1.50–1.61 (m, 2H), 1.75–1.82 (m, 4H),
1.85–1.93 (m, 2H), 2.11–2.20 (m, 2H), 2.29–2.39 (m, 2H), 2.75–2.81
(m, 2H), 5.83 (s, 2H), 6.42 (d, J = 15.4, 2H), 6.71 (d, J = 15.4, 2H) and
7.20 (s, 4H). 13C NMR (100 MHz, CDCl3): ı (E,E-3e) = 21.8, 29.8,
32.3, 35.3, 35.9, 36.3, 111.0, 124.2, 125.7, 126.1, 135.6 and 146.6.
GC–MS: m/z (rel. int., %) = 410 (M+, 52), 257 (14), 154 (12), 153
(100), 145 (14), 129 (11), 117 (12) and 97 (22). Anal. Calcd. for
C26H34S2: C, 76.04; H, 8.34. Found: C, 76.09; H, 8.79.
2.4.3.3. 4,4ꢀ-bis(2-((Cycloheptylidenemethyl)thio)ethenyl)biphenyl
(5c). Yield: 77%. Yellow solid, m.p.: 113–120 ◦C. E,E/Z,E: 6/1. IR
(KBr): ꢁ = 2920, 2847, 1589, 1492, 930, 830 and 779 cm−1 1H NMR
.
(400 MHz, CDCl3): ı (E,E-5c) = 1.42–1.74 (m, 16H), 2.33–2.40 (m,
8H), 5.91 (s, 2H), 6.50 (d, J = 15.5, 2H), 6.79 (d, J = 15.5, 2H), 7.33
(d, J = 8.2, 4H) and 7.51 (d, J = 8.2, 4H). 13C NMR (100 MHz, CDCl3):
ı (E,E-5b) = 26.7, 28.9, 29.2, 29.9, 32.2, 37.5, 114.3, 124.5, 125.9,
126.2, 126.9, 136.0, 138.9 and 147.5. GC–MS: m/z (rel. int., %) = 486
(M+, 100), 333 (17), 234 (13), 193 (16), 155 (12), 154 (25), 97 (51)
and 79 (20). Anal. Calcd. for C32H38S2: C, 78.96; H, 7.87. Found: C,
78.99; H, 8.01.
2.4.2.6. 1,4-bis(2-(((4-(tert-Butyl)cyclohexylidene)methyl)thio)
ethenyl)benzene (3f). Yield: 73%. Yellow solid, m.p.: 60–69 ◦C.
E,E/Z,E: 6/1. IR (KBr): ꢁ = 2943, 2859, 1589, 1366, 937, 841 and
775 cm−1 1H NMR (400 MHz, CDCl3): ı (E,E-3f) = 0.86 (s, 18H),
.
1.00–1.25 (m, 6H), 1.78–1.92 (m, 6H), 2.06–2.16 (m, 2H), 2.41–2.46
(m, 2H), 2.85–2.89 (m, 2H), 5.81 (s, 2H), 6.42 (d, J = 15.4, 2H), 6.73
(d, J = 15.4, 2H) and 7.21 (s, 4H). 13C NMR (100 MHz, CDCl3): ı
(E,E-3f) = 27.6, 28.0, 28.9, 30.4, 32.4, 36.5, 48.0, 110.5, 124.2, 125.8,
126.1, 135.6 and 147.1. GC–MS: m/z (rel. int., %) = 494 (M+, 64), 299
(12), 196 (15), 195 (100), 161 (10), 147 (16), 117 (26), 105 (12),
97 (29) and 57 (96). Anal. Calcd. for C32H46S2: C, 77.67; H, 9.37.
Found: C, 77.65; H, 9.93.
2.4.3.4. 4,4ꢀ-bis(2-((Cyclooctylidenemethyl)thio)ethenyl)biphenyl
(5d). Yield: 80%. Yellow solid, m.p.: 120–129 ◦C. E,E/Z,E: 6/1. IR
(KBr): ꢁ = 2920, 2847, 1589, 1443, 934, 833 and 779 cm−1 1H NMR
.
(400 MHz, CDCl3): ı (E,E-5d) = 1.44–1.59 (m, 12H), 1.63–1.76 (m,
8H), 2.30–2.37 (m, 8H), 5.94 (s, 2H), 6.49 (d, J = 15.5, 2H), 6.78 (d,
J = 15.5, 2H), 7.33 (d, J = 8.3, 4H) and 7.51 (d, J = 8.3, 4H). 13C NMR
(100 MHz, CDCl3): ı (E,E-5d) = 25.9, 26.2, 26.3, 26.6, 27.2, 31.1, 37.3,
114.5, 124.6, 125.9, 126.1, 126.9, 136.0, 138.9 and 147.9. GC–MS:
m/z (%) = 514 (M+, 54), 168 (12), 167 (100), 97 (38), 81 (21) and 79
(11). Anal. Calcd. for C34H42S2: C, 79.32; H, 8.22. Found: C, 79.24;
H, 8.31.
2.4.2.7. 1,4-bis(2-((2,2-Diphenylethenyl)thio)ethenyl)benzene (3g).
Yield: 57%. Yellow solid, m.p.: 97–107 ◦C. E,E/Z,E: 4/1. IR (KBr):
ꢁ = 3024, 1597, 1493, 1439, 930, 772, 752 and 698 cm−1 1H NMR
.
(400 MHz, CDCl3): ı (E,E-3g) = 6.57 (d, J = 15.5, 2H), 6.83 (s, 2H), 6.85
(d, J = 15.5, 2H) and 7.21–7.42 (m, 24H). 13C NMR (100 MHz, CDCl3):
ı (E,E-3g) = 122.1, 123.7, 126.1, 127.1, 128.3, 128.4, 129.7, 135.6,
139.0 and 141.2. GC–MS: m/z (rel. int., %) = 550 (M+, 33), 223 (13),
205 (21), 192 (43), 191 (28), 178 (42) and 165 (31). Anal. Calcd. for
2.4.3.5. 4,4ꢀ-bis(2-((4-Methylcyclohexylidenemethyl)thio)ethenyl)
biphenyl (5e). Yield: 78%. Yellow solid, m.p.: 110–120 ◦C. E,E/Z,E:
5/1. IR (KBr): ꢁ = 2916, 2847, 1589, 1493, 1439, 933, 833 and
783 cm−1 1H NMR (400 MHz, CDCl3): ı (E,E-5e) = 0.92 (d, J = 6.6,
.
C38H30S2: C, 82.87; H, 5.49. Found: C, 82.38; H, 5.73.
6H), 0.95–1.12 (m, 4H), 1.50–1.64 (m, 2H), 1.78–1.81 (m, 4H),
1.86–1.94 (m, 2H), 2.12–2.20 (m, 2H), 2.37–2.40 (m, 2H), 2.77–2.81
(m, 2H), 5.85 (s, 2H), 6.48 (d, J = 15.5, 2H), 6.78 (d, J = 15.5, 2H), 7.33
(d, J = 8.3, 4H) and 7.51 (d, J = 8.3, 4H). 13C NMR (100 MHz, CDCl3):
ı (E,E-5e) = 21.8, 29.8, 32.3, 35.3, 35.9, 36.3, 111.0, 124.7, 125.9,
125.9, 126.9, 136.0, 138.8 and 146.7. GC–MS: m/z (rel. int., %) = 486
(M+, 100), 333 (28), 193 (16), 155 (10), 154 (22), 107 (13), 97 (45),
91 (13), 81 (16) and 79 (17). Anal. Calcd. for C32H38S2: C, 78.96; H,
7.87. Found: C, 79.01; H, 8.10.
2.4.3. Synthesis of the 4,4-bis(((methyl)thio)ethenyl)biphenyl
derivatives 5a–g
NaOMe (4 mmol) was added to a stirred solution of the
corresponding (diphenylphosphinoyl) methyl ethenyl sulfide (1,
2.2 mmol) in THF (20 mL) at room temperature. After 20 min, the
system was treated with [1,1ꢀ-biphenyl]-4,4ꢀ-dicarbaldehyde (4,
1 mmol) and the solution was stirred under reflux for 3–5 h. A satu-
rated aqueous solution of NH4Cl (20 mL) was added and the mixture
was extracted with EtOAc (2× 20 mL). The combined organic layers
were dried (MgSO4), filtered and concentrated under reduced pres-
sure. The residue was purified by column chromatography, eluting
with hexanes.
2.4.3.6. 4,4ꢀ-bis(2-((4-(tert-Butyl)cyclohexylidenemethyl)thio)
ethenyl)biphenyl (5f). Yield: 80%. Yellow solid, m.p.: 147–155 ◦C.
E,E/Z,E: 12/1. IR (KBr): ꢁ = 2944, 1591, 1365, 933, 819 and 782 cm−1
.
1H NMR (400 MHz, CDCl3): ı (E,E-5f) = 0.87 (s, 18H), 1.02–1.25
(m, 6H), 1.79–1.92 (m, 6H), 2.09–2.19 (m, 2H), 2.43–2.47 (m, 2H),
2.86–2.90 (m, 2H), 5.84 (s, 2H), 6.49 (d, J = 15.4, 2H), 6.79 (d, J = 15.4,
2H), 7.34 (d, J = 8.4, 4H) and 7.52 (d, J = 8.4, 4H). 13C NMR (100 MHz,
CDCl3): ı (E,E-5f) = 27.6, 28.0, 28.9, 30.4, 32.5, 36.5, 48.0, 110.5,
124.7, 125.9, 125.9, 126.9. 136.0, 138.9 and 147.2. GC–MS: m/z
(%) = 570 (M+, 100), 375 (21), 196 (21), 193 (18), 149 (20), 111 (12),
97 (41), 91 (13) and 81 (16). Anal. Calcd. for C38H50S2: C, 79.94; H,
8.83. Found: C, 79.95; H, 8.85.
2.4.3.1. 4,4ꢀ-bis(2-((Cyclopentylidenemethyl)thio)ethenyl)biphenyl
(5a). Yield: 68%. Yellow solid, m.p.: 115–120 ◦C. E,E/Z,E: >20/1.
IR (KBr): ꢁ = 2951, 2862, 1589, 934, 822 and 783 cm−1 1H NMR
.
(400 MHz, CDCl3): ı = 1.66–1.78 (m, 8H), 2.31–2.43 (m, 8H), 6.00 (t,
J = 2.0, 2H), 6.48 (d, J = 15.5, 2H), 6.79 (d, J = 15.5, 2H), 7.34 (d, J = 8.3,
4H) and 7.52 (d, J = 8.3, 4H). 13C NMR (100 MHz, CDCl3): ı = 26.2,
26.7, 31.0, 34.3, 109.3, 124.5, 125.9, 125.9, 126.9, 136.0, 138.8 and
150.2. GC–MS: m/z (rel. int., %) = 430 (M+, 98), 306 (19), 305 (70),

M.M. Bassaco et al. / Journal of Photochemistry and Photobiology A: Chemistry 290 (2014) 1–10
5
Table 1
Optimization of the reaction conditions for the olefination of 2 toward the 1,4-bis(((methyl)thio)ethenyl)benzene derivative 3f.
Entry No.
Basea
Temperature
Time (h)
E,E/Z,E ratiob
Yield (%)c
1
2
3
4
5
6
NaH
NaH
NaOMe
NaOMe
nBuLi
nBuLi
r.t.
Reflux
r.t.
Reflux
r.t.
Reflux
24
5
24
5
24
3
1.5:1
2.3:1
1.3:1
3.7:1
2.5:1
6:1
78
72
45
57
70
73
a
Excess base (2 equiv.) was employed.
Determined by 1H NMR.
Isolated yields.
b
c
2.4.3.7. 4,4ꢀ-bis(2-((2,2-Diphenylethenyl)thio)ethenyl)biphenyl (5g).
Yield: 80%. Yellow solid, m.p.: 147–154 ◦C. E,E/Z,E: >20/1. IR
that, unlike the reaction of 1f with 2, the use of dialdehyde 4
afforded no product after 24 h, at room temperature, when NaH
was employed as the base (Table 2, Entry 1). However, addition of
HMPA to the reaction furnished 72% of the expected product in a
E,E/Z,E isomer ratio of 1.2:1 (Table 2, Entry 2). Inclusion of the addi-
tive could be omitted by carrying out the reaction under reflux,
which gave the anticipated bis vinyl sulfide 5f in 82% yield after
5 h, in a 5:1 E,E/Z,E isomer ratio (Entry 3).
Changing the base to potassium tert-butoxide favored the
formation of the Z,E isomer, but did not improve the reaction per-
formance (Entry 4), and the vinyl sulfide was obtained in 60%
yield (E,E/Z,E isomer ratio = 0.5:1). Finally, using NaOMe as base,
at room temperature, furnished 72% of the product (E,E/Z,E isomer
ratio = 5:1), after 24 h (Entry 5).
(KBr): ꢁ = 3024, 1597, 1493, 934, 822, 752 and 698 cm−1 1H NMR
.
(400 MHz, CDCl3): ı = 6.62 (d, J = 15.5, 2H), 6.83 (s, 2H), 6.88 (d,
J = 15.5, 2H) and 7.19–7.53 (m, 28H). 13C NMR (100 MHz, CDCl3):
ı = 122.1, 123.9, 126.2, 127.0, 127.1, 128.3, 128.4, 129.6, 135.6,
139.0, 139.2 and 141.2. GC–MS: m/z (rel. int., %) = 626 (M+, 1), 391
(23), 390 (71), 279 (11), 223 (22), 211 (17), 210 (22), 199 (51), 192
(100), 178 (90), 165 (54), 152 (26) and 121 (31). Anal. Calcd. for
C44H34S2: C, 84.30; H, 5.47. Found: C, 84.11; H, 5.96.
3. Results and discussion
3.1. Compound synthesis and characterization
Not unexpectedly, however, when the transformation was car-
ried out under reflux the diastereoselectivity increased and the
E,E/Z,E isomer ratio raised to 12:1 (Table 2, Entry 6). Notewor-
thy, the transformation took place in 3 h and 80% yield. Therefore,
the latter reaction conditions were used for the synthesis of the
biphenyl derivatives 5a–g, as shown in Scheme 2 and Table 3.
The optimized conditions of the Wittig–Horner reaction with
dialdehydes 2 and 4 were employed to synthesize a small library of
symmetrically substituted compounds the bis vinyl sulfides 3a–g
and 5a–g (Scheme 2), which were obtained in good to excellent
yields, as summarized in Table 3. Interestingly, the E,E isomers
were obtained exclusively when the five-membered ring-derived
reagent 1a was employed. In addition, the remaining examples
exhibited a clear preference for the E,E isomers, in agreement with
the selectivity observed for other Horner–Wittig reactions [21].
The structures of the vinyl sulfide derivatives were confirmed
after rigorous IR, 1H and 13C NMR analysis, as well as by their
HRMS and elemental analysis data. The magnitudes of the observed
coupling constants between the adjacent vinylic protons was
employed to infer the stereochemistry of the double bonds, while
the areas under the curves were used to estimate the corresponding
stereoisomeric ratios. The presence of minor amounts of geomet-
ric isomers accompanying the major E,E-product resulted in wide
melting point ranges of the compounds [22]a].
The Wittig–Horner olefination entails the reaction between an
ylide precursor and a carbonyl component. Accordingly, a series of
starting diphenylphosphinoyl derivatives (1a–g) were synthesized,
as ylide precursors, employing our previously reported procedure
[17a,18]. On the other hand, the symmetric dialdehydes terephtha-
laldehyde (2) and [1,1ꢀ-biphenyl]-4,4ꢀ-dicarbaldehyde (4), which
embody the aromatic cores of the proposed products, were used
as the starting carbonyl components. Compound 4 was included as
starting material on account that biphenyl derivatives have been
previously prepared as new materials for use in organic blue-light-
emitting diodes [20].
In order to optimize the proposed Wittig–Horner olefination
toward the expected 1,4-bis(((methyl)thio)ethenyl)benzenes (3),
the model reaction between the phosphinoyl derivative 1f and
dialdehyde 2 was studied in THF. Modifications were performed
in the reaction temperature and time, employing NaH, NaOMe and
nBuLi as bases.
As shown in Table 1, except for NaH, the yields were better when
the reaction was carried out under reflux. In addition, these con-
ditions allowed to attain improved stereoselectivities (entries 1, 3
and 5 vs. entries 2, 4 and 6, respectively), always being the E,E iso-
mer the most favored one. NaOMe afforded only moderate yields
(<60%) and stereoselectivity (E,E/Z,E up to 3.7).
On the other hand, the use of nBuLi under reflux proved to be the
most efficient conditions (Entry 6); despite giving chemical yields
essentially similar to those furnished by NaH (Table 1, Entries 1
and 2), these afforded improved product stereoselectivity (E,E/Z,E
diasteromer ratio = 6:1) under shorter reaction times. Therefore,
these optimized conditions were chosen for the synthesis 3a–g
(Scheme 2), with the results exhibited in Table 3.
Interestingly, compound 5g can be regarded as a vinylogous
of 4,4ꢀ-bis(2,2ꢀ-diphenylvinyl)-biphenyl (DPVBi) and related com-
pounds (Fig. 1), which act as blue light emitters [22b,c].
3.2. Photophysical characterization
The optical properties of the synthesized vinyl sulfides, includ-
ing their UV/vis spectra and fluorescence emission characteristics,
were studied in dilute CH2Cl2 solutions, at room temperature.
Next, the reaction was also optimized for the use of the biphenyl
derivative 4, with the results contained in Table 2. It was observed

6
M.M. Bassaco et al. / Journal of Photochemistry and Photobiology A: Chemistry 290 (2014) 1–10
O
S
2
O
R
S
R
S
nBuLi, THF, reflux
S
O
P
Ph
Ph
3a−3g
5a−5g
R
S
1a−1g
NaOMe, THF, reflux
R
R
O
O
4
R =
a
b
c
d
e
f
g
Scheme 2. Wittig–Horner synthesis of the proposed bis vinyl sulfides 3a–g and 5a–g.
The absorbance (ꢂmax) and emission (ꢂem) maxima, Stokes’ shifts
(ꢃꢂST), fluorescence quantum yields (˚F) and values of their molar
extinction coefficient (εmax) are summarized in Table 4.
3g, the same plot predicted ten chromophoric units, underesti-
mating the actual number. This may be a consequence of steric
interactions between hydrogens supported on adjacent rings of the
1,1ꢀ-ethene-1,1ꢀ-diyldibenzene system.
Fig. 2 shows the normalized excitation spectra of the sulfides
3a–g and 5a–g. Both series of compounds exhibited single absorp-
tion bands with quite similar characteristics. Except for compounds
3g and 5g, which are red-shifted when compared to the other sul-
fides (ꢂmax = 366 and 365 nm, respectively), the absorption peaks
were in the range of 350–355 nm, which can be assigned to the
On the other hand, the plot predicted approximately eight chro-
mophoric units, for 5a–f and ten for 5g, underestimating in all cases
the actual number. In the former case (5a–f), this may be a conse-
quence of the twisted structure of the biphenyl fragment, resulting
from a balance between ortho hydrogen–hydrogen steric repul-
sion and the electronic conjugation of the two phenyl rings, which
ends up furnishing a less effective ␲-conjugation of the whole sys-
tem [25]. However, in the case of 5g, steric interactions between
hydrogens supported on adjacent rings of the 1,1ꢀ-ethene-1,1ꢀ-
diyldibenzene system, may also be contributing to the observed
behavior.
Next, the photoluminescence properties of the sulfides 3 and
5 were investigated. Fig. 3 shows their normalized emission spec-
tra revealed that, when excited at their absorption maxima, the
compounds exhibit emission spectral profiles which mirror the
corresponding excitation spectra and display maxima in the vio-
let/blue region (421–441 nm), with a full width at half-maximum
averaging 85 nm and Stokes’ shift values between 4259 and
5498 cm−1 (0.53–0.68 eV). The latter are in the same range as those
reported for oligothiophenes (∼0.6 eV) [26], which were attributed
to significant differences in their geometries of the ground and
excited states [27].
1
typical ␲–␲* transitions of the whole molecule. Compared to
the cycloalkyl-terminated sulfides, their diphenyl end-capped con-
geners 3g and 5g also exhibited the largest extinction coefficients,
suggesting the presence of larger and more effective ␲-conjugated
systems, extended through the “sulfur bridge”.
The bathochromic shift experienced by compounds 3a–g with
regards to the spectrum of 1,4-diethenylbenzene [ꢂmax: 228, 236
and 279 nm (sh)] [23] clearly evidenced that the sulfur bridge
extends the conjugation of the system.
Dale [24] has shown that when the wavelength maxima (ꢂmax
)
of the main band of chain molecules consisting of alternating ben-
zene rings and ethylenic bonds is plotted against the number of
chromophoric units (benzene ring = 2; ethylenic bond = 1), they
follow a pattern; this can be fit by an exponential curve of the
form ꢂmax = A × (1−e−bx), where x is the number of chromophoric
units. Interestingly, interpolation of ꢂmax of compounds 3a–f in the
curve suggests the presence of an absorbing system with approx-
imately eight chromophoric units, consisting with the assignment
of a chromophoric unit to each one of the sulfur atoms (S = 1). For
The single and strong fluorescence band present in the fluo-
rescence spectra indicated that the emission takes place from the
Table 2
Optimization of the reaction conditions with dialdehyde 4, for the synthesis of the 4,4ꢀ-bis(((methyl) thio)ethenyl)biphenyl derivative 5f.
Entry No.
Basea
Solvent
Temperature
Time (h)
E,E/Z,E ratioc
Yield (%)d
1
2
3
4
5
6
NaH
NaH
NaH
KOtBu
NaOMe
NaOMe
THF
r.t.
r.t.
Reflux
r.t.
r.t.
24
24
5
1
24
3
–
0
72
82
60
72
80
THFb
THF
1.2:1
5:1
0.5:1
5:1
PhMe
THF
THF
Reflux
12:1
a
Excess base (2 equiv.) was employed.
HMPA (1 mL) was added to the reaction system.
Determined by 1H NMR.
b
c
d
Isolated yields.

M.M. Bassaco et al. / Journal of Photochemistry and Photobiology A: Chemistry 290 (2014) 1–10
7
Table 3
Synthesis of 1,4-bis(((methyl)thio)ethynyl)benzenes derivatives 3a–g and the related 4,4ꢀ-bis(((methyl)thio)ethynyl)biphenyls 5a–g.
Entry No.
Product No.
Product structure
Time (h)
E,E/E,Z ratioa
Yield (%)
H
H
S
H
S
H
H
H
1
2
3a
3b
5
5
>20:1
4:1
74
76
H
H
S
S
H
H
H
H
H
H
H
S
S
H
H
H
H
3
4
3c
4
4
7:1
80
60
H
H
S
S
H
H
H
H
3d
2.5:1
H
S
S
H
H
H H
5
6
3e
3f
3
3
6:1
6:1
72
73
H
H
S
S
H
H
H
H
H
H
S
H
S
H
H
H
7
3g
5
4:1
57
H
H
S
H
S
H
H
H
8
9
5a
5b
4
4
>20:1
10:1
68
80
H
H
H
S
S
H
H
H
H
H
S
H
S
H
H
H
10
11
5c
5
4
6:1
6:1
77
80
H
H
S
S
H
H
H
H
5d
H
H
S
S
H
H
H
H
12
13
5e
5f
3
3
5:1
78
80
H
H
S
H
S
H
H H
12:1
H
H
S
H
S
H
H H
14
5g
4
>20:1
80
a
Determined by 1H NMR.
lowest excited state with the largest oscillator strength [28]. These
sulfides displayed a trend similar to analogous biphenyl-based dyes
previously reported in literature; the small red-shifted absorption
and fluorescence emission maxima observed among these series
of related compounds is due to an increase in the electron mobil-
ity, influenced by the end-capping group, generally, an electron
donating group [29–32]. From the onset of the absorption peaks
(ꢂonset = 390–400 nm), the optical band gap Eg (Eg = 1240/ꢂonset
)

8
M.M. Bassaco et al. / Journal of Photochemistry and Photobiology A: Chemistry 290 (2014) 1–10
Table 4
Photophysical properties of compounds 3a–g and 5a–g, in CH2Cl2.
Compd. No.
UV–vis absorption
Fluorescence data
ꢂmax (nm)
εmax (104 M−1 cm−1
)
ꢂem (nm)
ꢃꢂST (cm−1
)
˚
(ꢂex = 347 nm)a
F
3a
3b
3c
3d
3e
3f
3g
5a
5b
5c
5d
5e
5f
350
350
353
355
350
351
366
352
351
353
352
353
350
365
5.10
4.33
3.43
0.81
4.98
2.77
4.90
4.79
6.52
5.15
2.55
6.36
3.75
7.10
424
421
422
424
427
422
435
431
433
434
437
432
432
441
4987
4818
4632
4584
5152
4793
4259
5368
5180
5368
5498
5180
5423
4722
0.021
0.048
0.109
0.018
0.027
0.031
0.058
0.182
0.238
0.176
0.122
0.283
0.233
0.143
5g
Values were computed with the samples in CH2Cl2 (ꢀ2D0 = 1.4242) with reference to a solution of quinine in 0.1 M H2SO4 (ꢀD20 = 1.3576); the experimental error was
a
0.004 [19].
Fig. 2. Overlapped, normalized UV/vis absorption spectra of vinyl sulfides 3a–g (top) and 5a–g (bottom) in CH2Cl2, at 25 ◦C.
Fig. 3. Normalized, overlapped emission spectra of vinyl sulfides 3a–g and 5a–g in CH2Cl2, at 25 ◦C.

M.M. Bassaco et al. / Journal of Photochemistry and Photobiology A: Chemistry 290 (2014) 1–10
9
was determined to be in the range 3.10–3.18 eV, which nears its
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4. Conclusions
In summary, we have successfully prepared a series of novel
vinyl sulfide derivatives and investigated their excitation and emis-
sion properties. The syntheses proceeded in good yields, through
the Wittig–Horner reaction of dialdehydes and (diphenylphos-
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We are grateful to FAPERGS, CNPq and CAPES for financial sup-
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