Synthesis and optical properties of various thienyl derivatives of pyrene

Article abstract of DOI:10.1007/s10895-013-1281-z

A series of various thienyl derivatives of pyrene were synthesized by Stille cross-coupling procedure. Their structures were characterized by ¹H NMR, ¹³C NMR and elemental analysis. The spectroscopic characteristics were investigated by UV-vis absorption and fluorescence spectra. Based on quantum chemical calculations, the energy levels of investigated molecules with respect to the pyrene molecule were also discussed.

Full text of DOI:10.1007/s10895-013-1281-z

J Fluoresc (2014) 24:153–160
DOI 10.1007/s10895-013-1281-z
ORIGINAL PAPER
Synthesis and Optical Properties of Various Thienyl
Derivatives of Pyrene
Krzysztof R. Idzik & Tobias Licha & Vladimír Lukeš &
Peter Rapta & Jaroslaw Frydel & Mario Schaffer &
Eric Taeuscher & Rainer Beckert & Lothar Dunsch
Received: 16 May 2013 /Accepted: 18 July 2013 /Published online: 6 August 2013
#
Springer Science+Business Media New York 2013
Abstract A series of various thienyl derivatives of pyrene
Introduction
were synthesized by Stille cross-coupling procedure. Their
1
structures were characterized by H NMR, 13C NMR and
Organic compounds containing extended π-conjugation have
received immense attention in recent years due to their unique
photophysical and charge transport properties, which make
them good material for potential applications in electronic
devices such as organic light emitting diodes (OLEDs)
[1–5], organic photovoltaics (OPV) [6–10] organic thin film
transistors (OTFT) [11–13], etc. They are also attractive due to
their promising two photon absorption [14, 15] and nonlinear
optical [16, 17] characteristics. Among the π-conjugated mo-
lecular materials, those containing polyaromatic hydrocarbons
(PAH), such as anthracene [18–20] perylene [21], pyrene
[22–24], pentacene [25, 26], etc., tethered with each other by
vinyl or acetylene linkages, are especially attractive due to
their flat π-stacking organization in the solid state. Direct
C−C linkage between the PAH has been found to be detri-
mental to the extension of conjugation as there is a loss of
coplanarity owing to the steric congestion [27].
elemental analysis. The spectroscopic characteristics were
investigated by UV–vis absorption and fluorescence spectra.
Based on quantum chemical calculations, the energy levels of
investigated molecules with respect to the pyrene molecule
were also discussed.
.
.
Keywords Stille cross-coupling procedure Absorption
UV–VIS Fluorescence spectroscopy Pyrene Thiophene
.
.
.
:
:
K. R. Idzik E. Taeuscher R. Beckert
Institute of Organic and Macromolecular Chemistry,
Friedrich-Schiller University Jena, Humboldstraße 10, 07743 Jena,
Germany
:
:
K. R. Idzik (*) T. Licha (*) M. Schaffer
The most attractive π-center within two-photon materials is
a pyrene moiety, not only because it is planar but also because
it has been extensively studied in various fields of chemical
biology. Moreover, due to durable electronic properties of the
pyrene moeiety, its derivatives have found applications in
microenvironmental sensors [28–30], liquid crystals [31, 32],
organic light-emitting diodes [33], photoactive polypeptides
[34], and genetic probes [35–37], and serve as components for
various types of fluorescent polymers and dendrimers [38–40].
The pyrene core is particularly interesting in this context
since it offers numerous possibilities of peripheral group mod-
ifications with profound consequences on the condensed-
matter structure. For example, non-substituted pyrene forms
monoclinic crystals, while tetraethynylpyrene derivatives of
Department Applied Geology, Geoscience Centre of the University
of Göttingen, Goldschmidtstr. 3, 37077 Göttingen, Germany
e-mail: krzysztof.idzik@pwr.wroc.pl
e-mail: tobias.licha@geo.uni-goettingen.de
:
V. Lukeš P. Rapta
Institute of Physical Chemistry and Chemical Physics, Slovak
University of Technology Bratislava, Radlinského 9, SK-812
37 Bratislava, Slovak Republic
:
P. Rapta L. Dunsch
Group of Electrochemistry and Conducting Polymers,
Leibniz-Institute for Solid State and Materials Research,
01171 Dresden, Germany
J. Frydel
VENITUR Sp. z o.o., ul Wawozowa 34 B, 31-752 Krakow, Poland

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J Fluoresc (2014) 24:153–160
phenylethynyl form liquid crystalline columnar phases [41],
and pyrenes similarly substituted with n-diethyleneglycolether
derivatives display a liquid phase at room temperature [42].
Perylene is a typical luminescence material which has been
investigated for several decades. However, selfquenching will
appear at high concentrations or pure crystals due to molecular
aggregation [43]. On the other side, the luminescence properties
of pyrene core might be modulated using the proper molecular
substitution, e.g. with the heterocyclic units. For example, the
linear oligo- or polythiophenes have both an excellent perfor-
mance when acting as a building material of organic solar cells
[44] and high hole mobility in organic field effect transistors [45].
Thiophene derivatives of pyrenes generally display promis-
ing optical and electrochemical properties. Organic π-
conjugated structures containing thiophene units undergo
both oxidation and reduction processes and play an
important role in the search for new materials and their
novel applications [44]. Oligothiophenes with well de-
fined structures have also received a great deal of at-
tention not only as an example of model compounds for
conducting polythiophenes, but also as a new class of
functional π-electron systems.
pyrene, 1,4-bis(2-thienyl)-pyrene, 1,3,6-tris(2-thienyl)-pyrene
and 1,3,6,8-tetra(2-thienyl)-pyrene. In this context, the or-
igin of the vibronic structure of pyrene and 1,3,6,8-
tetra(2-thienyl)-pyrene fluorescence spectra will be analyzed
using a simple model based on the Franck-Condon analysis.
Methods and Materials
Preparation
All chemicals, reagents, and solvents were used as purchased
from commercial sources without further purification. 1H NMR
and 13C NMR spectra were recorded in CDCl3 on 300, 500 and
600 MHz liquid state Bruker spectrometer. Chemical shifts are
denoted in δ unit (ppm) and referenced to the internal standard:
TMS (tetramethylsilane) at 0.0 ppm. The splitting patterns are
annotated as follows: s (singlet), d (doublet), t (triplet) and m
(multiplet). Preparative column chromatography was carried out
on glass columns of different sizes packed with silica gel: Merck
60 (0.035–0.070 mm). Melting points of the synthesized dyes
were determined using a Stuart smp 20 melting point apparatus.
The chemical structure and synthetic route of the pyrene
derivatives are illustrated in Scheme 1. Bromination of
pyrene (1) with one to four equivalents of bromine gave
the mono-, di-, tri-, and tetrabromopyrenes: 1-bromopyrene
(2), 1,6-dibromopyrene (3), 1,4-dibromopyrene (4), 1,3,6-
tribromopyrene (5), and 1,3,6,8-tetrabromopyrene (6) [45].
To gain deeper insight into the relations between the
structure and optical properties of the thienyl-pyrene deriva-
tives, we will present the comparative spectroscopic and the-
oretical study of six novel molecular materials based on a
pyrene core that is connected to thiophene units at the 1, 3,
6, and 8 positions: 1-(2-thienyl)-pyrene, 1,6-bis(2-thienyl)-
S
Br
(v
(i
2
7
S
Br
Br
Br
S
S
(vi
(ii
+
+
Br
S
3
4
8
9
S
S
Br
Br
(vii)
(iii
1
S
Br
10
5
S
S
Br
Br
Br
Br
(viii)
(iv
S
S
11
6
Scheme 1 Synthesis of pyrene derivatives, (i): Br2, DCM, (ii): 2 eq Br2,
DCM, (iii): 3 eq Br2, nitrotoluene, (iv): 4 eq Br2, nitrotoluene, (v): 2-
(tributylstannyl)thiophene, Pd(PPh3)4, toluene, (vi): 2 eq 2-(tributylstannyl)
thiophene, Pd(PPh3)4, toluene, (vii): 3 eq 2-(tributylstannyl)thiophene,
Pd(PPh3)4, toluene, (viii): 4 eq 2-(tributylstannyl)thiophene, Pd(PPh3)4,
toluene

J Fluoresc (2014) 24:153–160
155
Mono- and dibromopyrene were prepared in DCM, in
case of tri- and tetrabromopyrene we used nitrotoluene
as a solvent. Cross-coupling of these bromopyrenes with
2-(tributylstannyl)thiophene under the conditions of the Stille
reaction afforded mono-, bis-, tris-, and tetra(thienyl)pyrenes 7–
11. 2-(tributylstannyl)thiophene (2 – 2.0 mmol, 5 – 6.0 mmol, 6
– 8 mmol, 3 and 4 – 4 mmol) respectively and Pd(PPh3)4
(0.46 g, 0.4 mmol) were added under nitrogen to compound 2
or 5 or 6 or a mixture of non separated 3 and 4 (2.0 mmol)
dissolved in 150 mL of anhydrous toluene in a 250 mL round
two-bottom flask. The resulting mixture was stirred for
4 days at 110 °C. Subsequently, the mixture was cooled
down to room temperature. Water (100 mL) was added and
the resulting solution was extracted three times with 50 mL
of CHCl3. The combined organic layers were washed with
50 mL brine, dried over MgSO4 and evaporated until
brown oil appeared. The crude product (7–11) was purified
by column chromatography (hexane/AcOEt, 10:1). For prep-
aration of bis(thienyl)pyrenes we used a mixture of 1,6-
dibromopyrene (3) and 1,4-dibromopyrene (4). We success-
fully isolated 1,6-bis(thienyl)pyrene (8) from 1,4-
bis(thienyl)pyrene (9). These latter derivatives were purified
through a chromatography column. The structures of com-
pounds 7–11 were confirmed by NMR and elemental analysis.
The reactions were conducted under easy-to-perform, mild
conditions with moderate to good yields. Finally, the chemical
substitution leads to an increase of the melting points (m.p.)
what ensures the thermal stability of these materials.
125.1; 124.9. Elemental analysis for: C24H14S2 Calc.: C,
78.65; H, 3.85; S, 11.50. Found: C, 78.79; H, 3.73; S, 11.76.
1,3,6-Tris(2-thienyl)-pyrene (10) Yellow solid, 90 % yield,
m.p. 154–155 °C. 1H NMR (600 MHz, CDCl3): δ=8.53–8.45
(m, 3H); 8.12 (s, 1H); 8.16 (d, J=7.8 Hz, 1H); 8.10 (d,
J=7.8 Hz, 1H); 8.07 (d, J=9.6 Hz, 1H); 7.52–7.49 (m, 3H);
7.39–7.36 (m, 3H); 7.26–7.22 (m, 3H). 13C NMR (500 MHz,
CDCl3): δ=142.4; 142.0; 141.9; 131.1; 131.0; 130.2; 129.8;
129.5; 129.4; 129.3; 128.9; 128.8; 128.3; 128.2; 128.1; 127.5;
126.4; 126.3; 126.1; 125.8; 125.7; 125.5; 125.3; 124.9. Ele-
mental analysis for: C28H16S3 Calc.: C, 74.96; H, 3.59; S,
21.44. Found: C, 75.29; H, 3.67; S, 21.46.
1,3,6,8-Tetra(2-thienyl)-pyrene (11) Yellow solid, 80 %
yield, m.p. 291–292 °C. 1H NMR (300 MHz, CDCl3):
δ=8.52 (s, 4H); 8.24 (s, 2H); 7.53 (d, J=4.8 Hz, 4H); 7.41
(d, J=3.3 Hz, 4H); 7.28–7.24 (m, 4H). 13C NMR (500 MHz,
CDCl3): δ=141.9; 131.2; 129.8; 129.1; 128.4; 127.5; 126.5;
125.9; 125.8. Elemental analysis for: C32H18S4 Calc.: C,
72.42; H, 3.42; S, 24.16. Found: C, 72.58; H, 3.63; S, 24.19.
Optical Measurements
The UV/VIS absorbance spectra were recorded on a Cary 50
spectrophotometer (Varian) between 250 and 500 nm at a
scanning rate of 60 nm/min. Fluorescence spectra were
recorded on a Cary Eclipse spectrofluorometer (Agilent)
equipped with a xenon lamp excitation source. The excitation
was set at the maximum of the lowest excitation band in the
range 2.76–3.18 eV (450 to 390 nm). The scanning rate was
30 nm min−1 with a slit width for excitation and emission of
2.5 nm, respectively. The measurements were carried out at
20 0.1 °C in Peltier-thermostatted quartz cells (Hellma Ana-
lytics, Müllheim) having a path length of 1.0 cm.
1-(2-thienyl)-pyrene (7) colorless crystals, 95 % yield, m.p.
85–86 °C. 1H NMR (600 MHz, CDCl3): δ=8.48 (d, J=9.6 Hz,
1H); 8.18 (d, J=7.8 Hz, 1H); 8.17 (d, J=7.8 Hz, 2H); 8.09–
8.05 (m, 4H); 8.01 (t, J=7.5 Hz, 1H); 7.51 (dd, J=5.4, 1.2 Hz,
1H); 7.37 (dd, J=3.6, 1.2 Hz, 1H); 7.25 (dd, J=5.1, 3.3 Hz,
1H). 13C NMR (500 MHz, CDCl3): δ=142.5; 131.4; 130.9;
130.8; 129.7; 129.0; 128.4; 127.9; 127.8; 127.7; 127.4; 127.2;
126.1; 126.0; 125.2; 125.0; 124.9; 124.7; 124.5. Elemental
analysis for: C20H12S Calc.: C, 84.47; H, 4.25; S, 11.27.
Found: C, 84.72; H, 4.33; S, 11.31.
Quantum-Chemical Methods
The electronic ground (S0) and lowest (S1) state geometries of
the selected molecules were optimized at the Density Func-
tional Theory (DFT) [46] level of theory employing Becke’s
three parameter hybrid functional using the Lee, Yang and
Parr correlation functional (B3LYP) [47]. The vertical transi-
tion energies, oscillator strengths and corresponding gradients
between the initial and final states were computed by the Time
Dependent (TD)-DFT method [48]. The calculations of opti-
mal geometries were performed using the 6-31G(d) basis set
for C, H atoms and 6-31+G(d) basis set for S atom [49, 50]
(the energy cut-off of 5×10−4 hartree and the final root mean
square energy gradient below 4×10−4 hartree Å−1). These
calculations were done using Northwest Computational
Chemistry Package (NWChem) 6.1.1 program package [51].
Based on these calculations, the origin of vibronic structure in
experimental fluorescence spectrum of pyrene and largest
thienyl-pyrene derivate (11) was explained using the Franck-
1,6-Bis(2-thienyl)-pyrene (8) Yellow solid, 80 % yield,
1
m.p. 238–239 °C. H NMR (600 MHz, CDCl3): δ=8.49 (d,
J=9.0 Hz, 2H); 8.17 (d, J=7.8 Hz, 2H); 8.09 (d, J=7.8 Hz,
2H); 8.07 (d, J=9.6 Hz, 2H); 7.51 (d, J=4.8 Hz, 2H); 7.37 (d,
J=3.6 Hz, 2H) 7.04 (dd, J=4.8, 3.6 Hz, 2H). 13C NMR
(500 MHz, CDCl3): δ=142.5; 130.8; 130.1; 129.5; 128.8;
128.0; 127.8; 127.5; 126.3; 125.4; 125.1; 124.6. Elemental
analysis for: C24H14S2 Calc.: C, 78.65; H, 3.85; S, 11.50.
Found: C, 78.45; H, 3.92; S, 11.37.
1,4-Bis(2-thienyl)-pyrene (9) Yellow solid, 10 % yield,
1
m.p. 129–130 °C. H NMR(600 MHz, CDCl3): δ=8.50 (s,
2H); 8.18 (d, J=7.8 Hz, 2H); 8.10 (d, J=7.8 Hz, 2H); 8.08 (s,
2H); 7.51 (d, J=5.4 Hz, 2H); 7.37 (d, J=3.6 Hz, 2H); 7.25 (dd,
J=4.8, 1.8 Hz, 2H). 13C NMR (500 MHz, CDCl3): δ=142.4;
131.2; 129.8; 128.8; 128.6; 128.0; 127.6; 127.5; 126.2; 125.5;

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J Fluoresc (2014) 24:153–160
Table 1 The experimental absorption (λabs), fluorescence excitation (λexc) and fluorescence emission (λem) spectral characteristics for compounds 1, 7,
8, 9, 10 and 11. TD-B3LYP ΔE energies for the S0→S1 and S1→S0 transitions
Compound
λabs
ΔE(S0 → S1)
λexc
λem
ΔE(S1 → S0)
/nm
eV (nm)
/nm
/nm
eV (nm)
pyrene (1)
333a)
347
371
370
388
404
3.72 (333)
3.38 (366)
3.14 (395)
3.14 (395)
2.97 (418)
2.82 (440)
373 a)
425
3.45 (359)
2.97 (417)
2.70 (459)
2.77 (448)
2.66 (466)
2.43 (510)
1-(2-thienyl)-pyrene (7)
399
412
411
437
443
1,6-Bis(2-thienyl)-pyrene (8)
1,4-Bis(2-thienyl)-pyrene (9)
1,3,6-Tris(2-thienyl)-pyrene (10)
1,3,6,8-Tetra(2-thienyl)-pyrene (11)
437
438
461
471
a) measured in methanol [53]
Condon analysis based on the Poisson distribution and har-
monic approximation [52, 53].
The highest energy value is indicated for pyrene molecule
3.72 eV and the symmetry of this electronically allowed
tranistions is 11B2u. The consecutive addition of the lateral
thiophenes, leads to the red shift with the energies of 3.38 eV
(for 7) to 2.82 eV (for 11). The symmetry of the electronic
transition for the largest molecule 11 is 11Au. The next relative
high oscillator strengths are connected with the energies
4.65 eV for 1 (S0→S5), 4.30 eV for 7 (S0→S4), 4.21 eV for
8 (S0→S5), 3.92 eV for 9 (S0→S3), 3.78 eV for 10 (S0→S4)
and 3.68 eV for 11 (S0→S4).
These theoretical energies agree very well with the the
spectroscopic properties measured in chloroform solution.
As it is illustrated in Fig. 1, the absorption spectra of the
studied systems are formed from two main bands. The max-
ima of the lowest energy absorption bands for 7 to 11 are
located between 347 nm and 404 nm, depending on the
molecular structure and molecular size. The obtained charac-
teristic properties of the absorption maxima (λabs) are collect-
ed in Table 1. The maximum of the second absorption bands
are also changed with respect to the molecular size. The
Results and Discussion
The basic pyrene molecule is planar and it contains four fused
rings of D2h symmetry group. The B3LYP geometry optimi-
sation of the smallest molecule with one added thienyl ring (7)
showed that the mutual orientation of the thiophene moiety
with respect to the pyrene plane for the most stable conforma-
tion is Θ=48°. The thiophene ring is spatially oriented out of
the pyrene center. With respect to this fact, this arrangement
was also fixed for the next monomers. In the case of the
molecules 8, 9 and 11, the geometries were symmetric and
they belong to the C2 and C2h point of groups, respectively.
Based on the optimal DFTelectronic ground state geometries,
the vertical excitation energies were calculated. The energies
corresponding to the lowest S0→S1 tranistions have very
strong oscillator strengths and they are collected in Table 1.
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
7
8
9
10
11
270 280 290 300 310 320 330 340 350 360 370 380 390 400 410 420 430 440 450 460 470
Wavelength [nm]
Fig. 1 Normalized UV/VIS-absorption spectra of 7, 8, 9, 10, and 11 solvated in CHCl3

J Fluoresc (2014) 24:153–160
157
Fig. 2 B3LYP orbitals of
394 nm (3.14 eV), 0.737
contributing dominantly to the
lowest TD-B3LYP energy
tranistions (S0→S1 and S0→S4).
The depicted isosurface is 0.03
atomic unit. The values written in
italic are oscillator strengths.
Orbital symmetry is indicated in
the parentheses
11Au: HOMO(ag) → LUMO(au)
295 nm (4.21 eV), 0.1866
21Bu: HOMO–2(bg) → LUMO(au)
HOMO(ag) → LUMO + 1(bu)
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
7
8
9
10
11
0.0
380
390
400
410
420
430
440
450
Wavelength [nm]
Fig. 3 Normalized fluorescence excitation spectra of 7, 8, 9, 10, and 11 solvated in CHCl3

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J Fluoresc (2014) 24:153–160
1,0
0,9
0,8
0,7
0,6
0,5
0,4
0,3
0,2
0,1
0,0
7
8
9
10
11
400 410 420 430 440 450 460 470 480 490 500 510 520 530 540 550 560 570 580 590 600
Wavelength [nm]
Fig. 4 Normalized fluorescence emission spectra of 7, 8, 9, 10, and 11 solvated in CHCl3
corresponding wavelengths reported by Lukeš et al. [53] for
the pyrene molecule in methanol are 333 and 270 nm. Pyrene
with one thienyl group gives an absorption maximum at
347 nm, with two groups at approximately 370 nm, with
three—at 388, and with four—at 404 nm. Thus, an increasing
number of thienyl groups in the pyrene ring results in a
bathochromic shift.
In order to understand the effect of the molecular structure
on the absorption spectra of the largest molecule 11 for the two
lowest optical transitions with dominant oscillator strength, it
is useful to examine the relevant highest occupied (HOMO)
and lowest unoccupied (LUMO) molecular orbitals. These
orbitals were evaluated for B3LYP functional (see Fig. 2).
Our calculations showed that the electron transition S0→S1 fo
11Au symmetry is mostly connected with the excitation from
HOMO to LUMO. The HOMO orbital is regularly delocalized
over the outer carbon–carbon bonds of pyrene and thiophene
moities. On the other hand, the lobes of LUMO orbital are
perpendicularly oriented to the lobes of HOMO. The next
intensive optically allowed transition of 21Bu symmetry comes
from HOMO–2 to LUMO and HOMO to LUMO+1 orbitals.
As it is illustrated in Fig. 2, this electronic excitation shifts the
electron denisty from the lateral thiophene units to the pyrene
center.
The fluorescence excitation and steady-state emission spectra
of the thienylpyrenes were recorded also in chloroform (Figs. 3
and 4). In all cases, the comparable fluorescence activity was
observed. The substitution of hydrogens in the pyrene ring by
thiophene groups result in a bathochromic shift. The fluores-
cence excitation maxima (λexc) for compounds 7–11 are shifted
from 399 to 443 nm (see Table 1). Similar effect is also perceiv-
able in the experimental fluorescence emission band maxima
(λem). An increasing number of thienyl groups connected to
pyrene causes a displacement of the spectral band positions in
the fluorescence emission spectra from 425 to 471 nm (Fig. 4).
The corresponding fluorescence wavelength reported by Lukeš
et al. [53] for the pyrene molecule in methanol is 373 nm.
1.0
0.8
0.6
0.4
0.2
0.0
From the structural point of view, the electron excitation is
also responsible for the planarization of all monomers
(Θ≈36°). The next geometrical changes are also indicated
along the C–C and C–S bonds. The energies belonging to
the S1→S0 de-excitations have also very strong oscillator
strengths and they are collected in Table 1. These values are
also dependent on the number of thiophene units and they
agree with the corresponding experimental trends.
2.0
2.5
3.0
Energies / eV
3.5
Fig. 5 Calculated TD-B3LYP fluorescence S1→S0 vertical transition
with the vibrational replicas (see the solid lines) for the pyrene (1) and
1,3,6,8-tetra(2-thienyl)-pyrene (11). Normalized fluorescence spectrum
of pyrene molecule was measured in methanol [53]

J Fluoresc (2014) 24:153–160
159
To estimate the influence of the thienyl addition to the
pyrene moiety on the vibronic progression for de-excitation
S1→S0, the relevant Huang-Rhys factors were calculated
from the (TD)-B3LYP geometries and normal modes for the
molecules 1 and 11. The quantum mechanical B3LYP calcu-
lations of the molecular normal modes reveal that the observed
spectral structure for pyrene is dominated by a composite pro-
gression of the modes at 412, 597, 1277, 1450, 1686 and
3205 cm−1 with HR factors higher than 0.2. In the case of the
largest molecule 11, the theoretically determined modes are at
85, 508, 831, 849, 859, 1529 and 3231 cm−1. All these vibra-
tions belong to the Ag symmetry and they correspond to the C
−C aromatic ring deformations, CH out-of-plane vibrations, out-
of-plane CH and CCC bending and C–H stretching vibrations
(see Ref. 29 for pyrene modes). Based on the obtained TD-
B3LYP HR factors for 1 and 11, the relative intensities of the
replica were calculated for relevant normal modes and these
vertical lines were visualized with respect to the TD-B3LYP de-
excitation energy with the relative intensity being equal 1. The
depicted theoretical data (see solid lines in Fig. 5) show that the
presence of thienyl groups is evidently responsible for the
broadening of fluorescence emission band comparing to the
pyrene emission spectrum. These findings well correspond with
the experimental fluorescence records.
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In this work we have presented the synthesis and combined
theoretical and photophysical characteristics of the new molecu-
lar materials based on a pyrene core which was connected to
thiophene units. Following Stille cross-coupling procedure, we
obtained various thienyl derivatives of pyrene in good yield and
purity. Based on the theoretical and experimental results, we can
conclude that the optical properties of the whole synthesized
series depend evidently on the number of thienyl rings present on
the pyrene molecule. A typical red shift effect was observed
when the monosubstituted derivative displayed violet emission,
while the tetrathienyl pyrene exhibited blue emission. The theo-
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symmetry serve as coupling modes to the allowed electronic
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Project (SNIB, MTKD-CT-2005-029554). This support is gratefully ac-
knowledged. The presented study was partially funded by the German Federal
Ministry of Environment (promotional reference No. 0325417, Reaktherm).
For the financial support Peter Rapta and Vladimír Lukeš thank the
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