The optical properties and quantum chemical calculations of thienyl and furyl derivatives of pyrene

Article abstract of DOI:10.1039/c5cp03013g

A detailed electrochemical, photophysical and theoretical study is presented for various new thienyl and furyl derivatives of pyrene. Their optical properties are described based on UV-VIS absorption and both steady-state and time-resolved fluorescence spectroscopy. DFT and TDDFT calculations are also presented to support experimental data. The calculations results show that HOMO-LUMO orbitals are delocalized uniformly between aromatic core and aryl substituents. Good electrochemical stability of thienyl and furyl hybrids of pyrene confirm their potential application for light emitting electrochemical cells or spintronics mainly due to their beneficial optical and charge transport properties in electrochromic devices. In order to demonstrate this potential, an OLED device is presented. Synthesized compounds included in this OLED device both facilitate electron transport and act as a light emitting layer.

Full text of DOI:10.1039/c5cp03013g

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Physical Chemistry Chemical Physics
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DOI: 10.1039/C5CP03013G
Optical properties and quantum chemical calculations of thienyl
and furyl derivatives of pyrene
a,*
b
c
d
Krzysztof R. Idzik , Piotr J. Cywiński , Wojciech Kuznik , Jaroslaw Frydel ,
a
e
Tobias Licha , Tomasz Ratajczyk ,
a
Geoscience Centre of the University of Göttingen, Dept. Applied Geology, Goldschmidtstr.
3, 37077 Göttingen, Germany
b
Functional Materials and Devices, Fraunhofer Institute for Applied Polymer Research,
Geiselbergstr. 69, 14476 PotsdamꢀGolm, Germany
c
Czestochowa University of Technology, Faculty of Electrical Engineering, Armii Krajowej
17, 42ꢀ201 Czestochowa, Poland
d
VENITUR Sp. z o.o., Wawozowa 34 B, 31ꢀ752 Krakow, Poland
Polish Academy of Sciences, Institute of Physical Chemistry, Kasprzaka 44/52, 01ꢀ224
e
Warsaw, Poland
Author to whom correspondence should be addressed:
*
Eꢀmail:
krzysztof.idzik@pwr.wroc.pl
1

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Abstract: A detailed electrochemical, photophysical and theoretical study is presented for
various new thienyl and furyl derivatives of pyrene. Optical properties as well as their energy
levels were investigated using UVꢀVIS absorption and fluorescence spectroscopy.
Furthermore, DFT and TDDFT calculations are presented to support experimental data. It is
demonstrated that HOMO ꢀ LUMO orbitals are delocalized uniformly between aromatic core
and aryl substituents. Additionally, an OLED was build using synthesized compounds to
facilitate electron transport and act as light emitting layer. Good electrochemical stability of
thienyl and furyl hybrids of pyrene confirm their potential application, mainly due to their
optical and charge transport properties in electrochromic devices, light emitting
electrochemical cells, and spintronics.
Keywords: Pyrene, UVꢀVIS, fluorescence spectroscopy, DFT calculations, TDDFT
simulations, OLED
1
. Introduction
Organic materials possessing an extended πꢀconjugation have received immense
attention in recent years. This is due to their unique photophysical and charge transport
properties, which make them potential materials for applications in electronic devices such as
1
–8
9−15
organic light emitting diodes (OLEDs) , organic photovoltaics (OPV) , or organic thin
1
6−20
film transistors (OTFT)
. Further, they are attractive due to their promising two photon
21–24
21–24
absorption
and nonlinear optical
characteristics.
Fluorescence probes based on pyrene moieties have attracted considerable attention
2
5–32
over the past decades
. The pyrene ring is of special interest because its hydrogen atoms
2

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can easily be substituted using a wide range of chemical groups, particularly aryl groups such
as thiophene or furan. The pyrene structure is well studied and has been intensively examined
in the fields of biology, chemistry and physics. Moreover, due to its electro conductive
properties, pyrene and its derivatives have been successfully applied as micro environmental
33–36
37,38
39
sensors
, liquid crystals , and photoactive polypeptides . Pyrene is a flat aromatic
molecule and exhibits excellent fluorescent properties. Its pure blue emission already permits
4
0
its exploitation for its use in OLEDs . The pyrene core is particularly interesting in this
context, since it offers numerous possibilities of peripheral group modifications with profound
consequences on the condensedꢀmatter structure. For example, unsubstituted pyrene forms
monoclinic crystals, while tetraethynylpyrene derivatives of phenylethynyl form liquid
4
1
crystalline columnar phases , and pyrenes similarly substituted with diethyleneglycolether
42
derivatives display a liquid phase at room temperature . Pyrene is an efficient luminescent
material, which has been investigated for several decades. However, selfꢀquenching can be
observed at high concentrations or pure crystals due to a molecular aggregation via πꢀ
4
3–45
stacking
. However, the luminescence properties of the pyrene core might be modulated
using the proper molecular substitution, e.g., with heterocyclic units.
Organic πꢀconjugated structures containing thiophene units play an important role in
46
47, 48
the search for new materials and their novel applications such as organic solar cells
or
49
organic field effect transistors . Thiophenes with wellꢀdefined chemical structures have
recently attracted great attention not only as an example of model compounds for conducting
50–56
materials, but also as a new class of functional πꢀelectron systems
.
Furanꢀbased polymers are among the most widely used πꢀconjugated systems in
organic electronic devices. For example, polymers containing furyl groups have an excellent
5
7
performance when acting as building material for a highly efficient OLED . Another reason
for using furan is its lower resonance stabilization energy compared to benzene. Thus,
3

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chromophores with furan moieties proved to display a molecular hyperpolarizability, which is
58
higher than their benzene analogues . Oligofurans with wellꢀdefined structures have also
received great attention, not only exemplarily as model compounds for conducting polyfurans,
but also as a new class of functional πꢀelectron systems.
Considering the current literature, one can conclude that, when compared to other
59–66
heteroaromatics such as thiophene or pyrrole, furan has great potential for further studies
.
This may partially be attributed to the chemical lability of furan and its derivatives. For
example, furan serves as a diene in the [4+2] Diels–Alder reactions under milder conditions
6
7
than those for thiophene and pyrrole . On the other hand, the relatively lower aromaticity of
furan compared to those of thiophene and pyrrole may give rise to different electronic
68
properties in the resulting furanꢀbased materials .
Over the last decade, highly efficient blue OLEDs have attracted considerable
69–75
attention due to their potential applications in full color ultraꢀthin flat panel displays
.
Organic light sources are currently made from either low molecular weight organic materials
or polymers. For the former, the layer structure of the OLED is usually deposited on a rigid
7
6–79
base made from glass or metal
.
Suzuki, Stille, Kumada, and Negishi coupling reactions are wellꢀdescribed synthetic
methods that are often used to prepare electroactive compounds. In this paper, we also present
a series of symmetric molecules in which a pyrene core is connected to thiophene and furan
units. All compounds were obtained by the Stille crossꢀcoupling reaction. Furthermore, we
describe DFT calculations and TDDFT simulations of molecular materials based on a pyrene
core which is connected to thiophene and furan units. We also report the results of UVꢀVIS
and fluorescence spectroscopy measurements for the obtained compounds. Additionally, we
present a fully functioning OLED device using synthesized low molecular weight material to
act as electron transport and light emitting layer (Figure 1).
4

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2
. Methods and Materials
2
.1.
Synthesis
All chemicals, reagents, and solvents were used as received from commercial sources without
further purification. Melting points of the synthesized dyes were determined using Stuart smp
20 melting point apparatus.
2
.2.
Optical measurements
Electronic absorption spectra were collected on a UVꢀVIS absorption spectrometer
Lambda 35 (Perkin Elmer, Rodgau, Germany). The spectra were corrected with solvent
absorption spectra to obtain final absorption spectra for the studied compounds. Steadyꢀstate
fluorescence emission spectra were collected on an FLS920ꢀstm spectrometer (Edinburgh
Instruments, Livingstone, United Kingdom). The spectra were detector response corrected.
Fluorescence decays were also acquired on the FLS920ꢀstm spectrometer using the Time
Correlated Single Photon Counting (TCSPC) technique with a subꢀnanosecond pulsed LED
(EPLED 320) as an excitation source. Fluorescence decay times were determined from the
decays using the least square fit method. The fitting was assumed to be correct when the
2
goodnessꢀofꢀfit value χ was lower than 1.2. Fluorescence quantum yields were measured on
a C9920ꢀ02G absolute quantum yield (Φ) measurement system from Hamamatsu
(
Hamamatsu Photonics Deutschland GmbH, Herrsching am Ammersee, Germany). All
measurements were performed using a 3 ml quartz cuvette (Hellma GmbH, Germany) with
cm light path. All measurements were done for samples with optical densities below 0.15.
1
2
.3.
Quantum-chemical calculations
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All quantum mechanical calculations were made at the DFT level using the GAUSSIAN09
80
81
package and GABEDIT 2.4.6 Graphical User Interface . The 6ꢀ31G* basis set and the
B3LYP functional were used. The polarizable continuum model (PCM) was used in all
82
calculations to account for the solvent influence (chloroform) . The absorption and emission
spectra and excited state geometries were obtained from time dependent DFT (TDDFT)
singlet calculations. The reported lowest unoccupied molecular orbitals (LUMO) energy
values are read as DFT highest occupied molecular orbitals (HOMO) level reduced by the
TDDFT energy gap.
2
.4.
OLED preparation
−1
Indium tin oxide (ITO)ꢀcoated glass with a sheet resistance of about 8−12 ꢁ sq (Sigmaꢀ
Aldrich) was used for preparing the OLED, while the cathode was made from Al. The holeꢀ
conductive layer (HTL) was PEDOT: PSS (poly (3,4ꢀethylenedioxythiophene): poly
(styrenesulfonate) (SigmaꢀAldrich). Synthesized low molecular materials were used for the
preparation of the lightꢀemitting layer (EML). All measurements were performed using
laboratory power supply EAꢀPS 2032ꢀ025 (Figure 1).
3
. Results and discussion
3
.1.
Synthesis
The chemical structure and synthetic route of the pyrene derivatives are illustrated in Scheme
. Bromination of pyrene (1) with one to four equivalents of bromine gave the monoꢀ, diꢀ, triꢀ,
1
and tetrabromopyrenes, respectively. The bromination resulted in: 1ꢀbromopyrene (2), 1,6ꢀ
dibromopyrene (3) or 1,4ꢀdibromopyrene (4), 1,3,6ꢀtribromopyrene (5), and 1,3,6,8ꢀ
2
1
tetrabromopyrene (6) , respectively. Monoꢀ and dibromopyrene were prepared in DCM,
6

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while in the case of triꢀ and tetrabromopyrene we used nitrotoluene as a solvent. Crossꢀ
coupling of these bromopyrenes with 2ꢀ(tributylstannyl)furan under the conditions of the
Stille reaction gave monoꢀ, bisꢀ, trisꢀ, and tetrakis(furyl) pyrenes 7-11, respectively. For
preparation of di(furyl)pyrenes we used a mixture of 1,6ꢀdibromopyrene (3) and 1,4ꢀ
dibromopyrene (4). We successfully isolated 1,6ꢀdi(furyl)pyrene (8) from 1,4ꢀdi(furyl)pyrene
(9). Instead of 2ꢀ(tributylstannyl)furan we used 2ꢀ(tributylstannyl)thiophene to prepare the
thienyl derivative of pyrenes 12ꢀ15. The reactions were conducted under easyꢀtoꢀperform,
mild conditions with moderate to good yields. All compounds studied in this work were
obtained by the Stille crossꢀcoupling methodology according to the procedure reported in our
83–86
previous work (Scheme 1)
. Table 7 presents melting points of the synthesized dyes.
3
.2.
Optical measurements
Electronic absorption spectra collected for thienyl and furyl derivatives are shown in Figure 2
and in Figure 4, respectively. Unlike for pyrene itself, for which three bands are observed in
its absorption spectrum, most of the studied thienyl and furyl derivatives have only two
absorption bands.
The derivative containing four thiophenes exhibits similar absorption features as pyrene,
however, the spectrum displays a significant red shift. This feature can be associated with
pyrene or furan electron transitions mixed with the transitions characteristic for thiophene.
Depending on the derivative, the higher energy transitions (presumably π→π *) can be
observed in the range of 280−315 nm, while the lower energy transitions (presumably n→π
*)
can be found in the spectral range between 350 nm and 405 nm. The n→π* transitions can be
associated to the presence of heteroatoms (O or S) within the dye structures. A bathochromic
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shift can also be observed with an increasing number in electronꢀdonating thiophene or furan
moieties within the chemical dye structure. However, for the thienyl derivatives the observed
shift is lower than the one for furyl derivatives. For the higher energy band the shift is
approximately 35 nm for thienyl and 50 nm for furyl derivatives, while for the lower energy
band the shift is respectively larger with 55 nm and 75 nm, respectively. Both, hyperchromic
effect and hypochromic effect, are also observed for molecules with different numbers of
thiophene moieties. Both effects can be associated with the structural symmetry. In nonꢀ
symmetrical systems, the absorption increases with the number of thiophene moieties, while
for symmetrical molecules it decreases. Depending on the derivative and the investigated
absorption band, molar extinction coefficients (ε) determined based on the BeerꢀLambert law
−1
−1
were found in the range of 24.000–40.000 M cm for thienyl derivatives and in the range of
−1
−1
2
9.000–42.000 M cm for furyl derivatives. Noticeably, the ε values are basically in the
same order of magnitude as the corresponding values for pyrene itself. The summary of
parameters determined for thienyl and furyl derivatives based on absorption measurements are
presented in Table 1 and Table 2, respectively.
Steadyꢀstate fluorescence emission spectra collected for thienyl and furyl derivatives
are shown in Figure 3 and in Figure 5, respectively. For both classes of compounds, a
bathochromic shift is observed with an increasing number of electronꢀdonating (thiophene or
furan) groups and the relative ratios between corresponding peaks are different for different
derivatives. Noticeably, when two substituents are present within the chemical structure either
in cis or trans form, the fluorescence emission spectra are identical, which shows that the
position of substituent has no effect on the emission frequencies. This effect has been
observed both for thienyl and furyl derivatives. Importantly, pyrene emission is still
dominating in the emission observed for derivatives with only one side group, but for the
derivative with four substituents the spectrum is almost completely merged into one bold
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spectrum, even though the separate peaks can still be recognized. The spectra collected for
derivatives with 2 and 3 substitutes are more structured. The merging effect can be associated
with decreasing energies due to radiationless deactivation. In all cases, the third band on the
spectra stays virtually unaffected and only a red shift is observed for it. Independent from the
spectral features similar for both classes of compounds, significant differences in
photophysical properties can be noticed when quantum yields (
Φ
) and decay times (τ ) are
considered. The thienyl derivatives exhibit significantly lower
Φ
(70% vs 20%) and much
shorter fluorescence lifetimes (from 0.4 to 0.95 ns compared to ~2 ns) when compared to their
furanꢀsubstituted counterparts. Noticeably, the fluorescence quantum yield is virtually
independent from the number of substituents and their orientation (cis or trans). For the
thienyl derivatives the nonꢀradiative processes rate constant k is on average 5 times larger
nr
than the radiative processes rate constant k , while for the furyl derivatives k was on average
f
f
two times greater than knr. This result is a clear evidence for the domination of the nonꢀ
radiation processes in the deactivation path of thienyl derivatives. In comparison to furyl
−1
derivatives, the thienyl derivatives have larger Stokes shifts on average of about 1000 cm .
This is another evidence for the domination of nonꢀradiative processes in the thienyl based
systems. All the photophysical properties determined for thienyl and furyl pyrene derivatives
based on fluorescence measurements are also summarized in Table 1 and Table 2,
respectively.
3
.3.
Quantum-chemical methods
3.3.1. Thienyl derivatives of pyrene
The results of the DFT calculations are presented in Figures 6 and Figure 7 as well as in Table
3
and Table 4. All of the studied molecules are optically active, they absorb light in the UVꢀ
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violet spectral range and emit in the violetꢀblue part of the spectrum. Noticeably, the
theoretical TDDFT predictions are in good agreement with experimental absorption and
fluorescence spectra apart from the underestimation of the energy gap by 0.35 eV (equivalent
to approximately 70 nm). However, this deviation is often encountered in DFT calculations.
Nonetheless, the trend along the series K1ꢀK5 is well reproduced in the theoretically derived
spectra, including the very close overlapping of K1 and K3 in both absorption and emission
spectra. The order of the rising energy gap is K2<K5<K1=K3<K4. This is clearly connected
to the number of thiophene substituents adding their electrons to the molecular conjugate
system. Interestingly, the overlap of K1 and K3 spectra indicate that in the case of an isomer
mixture the relative position of the substituents does not influence the energy levels of
HOMO and LUMO orbitals as the substituents contribute to the molecular orbitals in similar
manner (see also Table 3 and Table 4).
HOMO and LUMO orbitals are distributed throughout the whole molecule for all
studied compounds (Table 4), which is due to the partially planar structures of both ground
and excited state (Table 3). The large overlap between HOMO and LUMO orbitals results in
quite efficient absorptions and emissions.
3
.3.2. Furyl derivatives of pyrene
Optical properties of the studied compounds K6ꢀK10 obtained from TDDFT
calculations confirm the influence of each additional furan substituent on absorption and
emission properties (Figure 8, and Figure 9, Table 5). The TDDFTꢀpredicted UVꢀVIS
absorption spectra presented in Figure 8 are in very good agreement with experimental data
apart from the underestimation of the energy gap by approximately 0.4 eV commonly
encountered in such calculations. Nevertheless, the relative spectral positions of the lowest
10

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energy absorption peak, attributed by the TDDFT calculation to the HOMOꢀLUMO
transition, are reproduced well in the calculation. The order of rise in energy gap is
K7<K10<K6=K8<K9 and this is also found in the emission spectra, both theoretically
derived and experimentally observed (Figure 9). It is quite clear that the HOMOꢀLUMO
energy gap and the related optical properties depend on the number of furene substituents
attached to the pyrene molecule. Interestingly, the spectra measured for the K6 and K8
compounds with two furyl units in transꢀ and cisꢀ positions respectively, are nearly
overlapping. Apparently, the contribution of the furyl substituents to the crucial HOMO and
LUMO orbitals is independent from their position in the compounds, as can be seen in
Table 6.
3
.4.
OLED preparation
Figure 1 shows the layer structure of the OLED device with details on the used organic
compounds and the function of each layer. Indium tin oxide (ITO)ꢀcoated glass (size 5 × 5
−
1
cm) with a sheet resistance of about 8–12 ꢁ sq was used as the backing material. ITO
deposited on the glass was cleaned by sonication in a detergent solution and then rinsed using
deꢀionized water.
An
aqueous
solution
of
PEDOT/PSS
(poly(3,4ꢀ
ethylenedioxythiophene)/poly(styrenesulfonate)) (HTL) forming a hole conductive layer, was
deposited onto ITO. Then water was removed under low pressure in a nitrogen atmosphere.
The lightꢀemitting layer (EML) (thienyl and furyl derivatives of pyrene) was deposited on the
cathode, which was an aluminum plate of the size 0.5 × 0.5 cm. Plates were superimposed to
each other. Then, the device was connected to a DC power source and a 24 V voltage was
passed through it to give a current equal to 0.2 A. A bright light with a color characteristic for
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the corresponding pyrene derivatives was observed under such conditions. Figure 10 displays
the working diode prepared using 1,3,6,8ꢀtetra(2ꢀfuryl)ꢀpyrene as an active emitting layer.
4
. Conclusions
In this work we presented photophysical properties and theoretical calculations for two new
classes of low molecular weight materials based on a pyrene core substituted either with
thiophene or furan units. All studied molecules can absorb light in the UV or violet visible
range and emit in the blueꢀviolet spectral region. We observed that the replacement of the
thiophene by furan increases the fluorescence quantum yield, most likely due to the more
planar structure of the former allowing for a efficient contribution of the π electrons.
Furthermore, we described DFT calculation and TDDFT simulations for the presented
materials. These quantumꢀchemical calculations fully support obtained experimental data.
HOMO and LUMO orbitals are delocalized uniformly on the pyrene core and its aryl
substituents. Theoretical calculations provided values for the HOMOꢀLUMO gaps for the
neutral states of the compounds. Compounds described in this paper fulfill the technological
requirements for materials to be successfully applied in the construction of organic–electronic
devices as demonstrated by the OLED device presented in this paper. In order to verify the
practical usefulness of the synthetized materials we built a prototype diode (OLED) using
thienyl and furyl derivatives of pyrene and also bithienyl derivatives of triazine. Obtained
OLEDs emitted blue light at a voltage of 12V and a yellow light at a voltage of 24V.
Following the physicoꢀchemical measurements and a successful practical application in
OLEDs, the synthesized heterocyclic units can be used as innovative, efficient, costꢀeffective
and environmentally friendly (mercury free) materials for light sources. These units can be
flexibly designed and emit a broad spectrum of visible light, when appropriately tuned. The
manufacturing of this type of light sources is one of the global research priorities, because it is
12

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based on a combination of new organic materials and economic production methods, thus
enabling a variety of innovative products to be designed. Considerable progress in
nanotechnology that has been made in recent years has resulted in the launch of the first
electronic products made of organic materials.
Acknowledgements
This work was supported within the research grant no 2011/01/N/ST4/02251 from National
Science Centre, Poland. Calculations have been carried out in Wroclaw Centre for
Networking and Supercomputing (http://www.wcss.wroc.pl, grant No.135). The presented
study was partially funded by the German Federal Ministry of Environment (promotional
reference No. 0325417, Reaktherm).
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7
8
= (K9): R1
=
, R
2
= R
3
= R
4
= H
= H
O
= (K6): R1 = R4
= (K8): R1 = R2
=
=
, R = R
2 3
O
O
R1
R3
R2
R4
Sn(Bu) , Pd(PPh )
O
3
3
4
9
, R
3
= R
4
= H
toluen, N2
10 = (K1): R1 = R2 = R3
=
, R = H
4
O
X1
X3
X2
Br2
11 = (K7): R1
= R2 = R3 = R4 =
O
X4
, R2 = R3 = R4 = H
12 = (K4): R1
=
1
S
R1
R2
2
:
:
:
:
:
X1 = Br, X2 = X3 = X4 = H
Sn(Bu) , Pd(PPh )
, R2 = R3 = H
S
3
3
4
13 = (K1): R
1
= R =
4
3
4
5
6
X1 = X = Br, X2 = X3 = H
4
S
X1 = X2 = Br, X3 = X4 = H
X1 = X2 = X3 =Br, X4 = H
X1 = X2 = X3 = X4 = Br
toluen, N2
R3
R4
14 = (K3): R
= R
=
, R3 = R4 = H
1
2
S
=
15 = (K5): R1 = R2 = R3
, R = H
4
S
16 = (K2): R1 = R2 = R3 = R4 =
S
Scheme 1. Synthesis of thienyl and furyl derivatives of pyrene.
Figure 1. OLED structure with the detail of the organic materials and them function used in
each layers.
20

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50000
40000
30000
20000
10000
0
K1
K2
K3
K4
K5
250
300
350
400
450
500
wavelength (nm)
Figure 2. Electronic absorption spectra for all pyrene thiophene derivatives in chloroform (in
ex. coefficient units).
1,0
0,8
0,6
0,4
0,2
0,0
K1 λexc = 370 nm
K2 λexc = 400 nm
K3 λexc = 370 nm
K4 λexc = 350 nm
K5 λexc = 390 nm
350
450
550
650
wavelength [nm]
Figure 3. Normalized fluorescence emission spectra for all dyes in chloroform.
21

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Table 1. Absorption and emission properties of the studied thienyl derivatives of pyrene.
Name/
Struktur
λabs
(nm)
ε
λem
Φ
ꢀν
k
f
k
nr
8 ꢀ1
ꢀ
1
ꢀ1
ꢀ1
τ (ns)
8
ꢀ1
(M cm )
(nm) (%)
(cm )
(10 s ) (10 s )
K1
K2
K3
2
3
92
72
24000
435
1
9.7
3893
0.40
4.9
20.1
34000
461
2
3
4
68
15
06
28000
31000
36000
470
22.0
3354
0.46
4.8
17.0
2
3
95
72
27000
34000
435
461
2
2.2
3893
0.61
3.6
12.8
2
80
48
25000
26000
4
05
15.1
4044
0.95
1.6
8.9
3
K4
K5
S
3
3
05
90
27000
40000
446
464
S
1
8.1
3220
0.43
4.2
19.0
S
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4
4
4
4
4
5x10
4x10
3x10
2x10
1x10
K06
K07
K08
K09
K10
0
250
350
450
550
Wavelength [nm]
Figure 4. Electronic absorption spectra for all dyes in chloroform (in ex. coefficient units).
1
0
0
0
0
0
,0
,8
,6
,4
,2
,0
K6 λ = 390 nm
ex
K7 λ = 330 nm
ex
K8 λ = 390 nm
ex
K9 λ = 360 nm
ex
K10 λ = 400 nm
ex
350
450
550
650
wavelength [nm]
Figure 5. Normalized fluorescence emission spectra for all dyes in chloroform.
23

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Table 2. Absorption and emission properties of the studied furyl derivatives of pyrene.
Name/
Structure
λabs
(nm)
ε
λem
Φ
ꢀν
k
f
k
nr
8 ꢀ1
ꢀ
1
ꢀ1
ꢀ1
τ (ns)
8
ꢀ1
(M cm )
(nm) (%)
(cm )
(10 s ) (10 s )
K6
2
3
97
90
31000
433
6
7.1
2546
1.6
4.2
2.1
42000
463
K7
3
4
30
30
32000
32000
4
79
65.8
2379
1.8
3.7
1.9
K8
2
3
99
88
30 000
33 000
433
463
6
8.7
2679
1.9
3.6
1.6
2
89
62
29000
29000
403
423
3
8.2
2810
3.3
1.2
1.9
3
K9
K10
3
4
15
10
35000
39000
460
480
6
3.2
2651
1.7
3.7
2.3
24

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Table 3. Molecular parameters derived from (TD)DFT calculations.
Average dihedral angle
Eg (absorption) Eg (Emission) between the central moiety
HOMO
eV]
LUMO (=Eg-
HOMO) [eV]
[
[eV/nm]
[eV/nm]
and the substituents in
ground/excited state [deg]
K1
K2
K3
K4
K5
-5.23
-5.15
-5.23
-5.30
-5.18
-2.25
-2.47
-2.25
-2.08
-2.37
2.97 /417
2.68 /463
2.98/ 416
3.22 / 384
2.81/ 440
2.39 /518
2.16/ 573
2.39/ 518
2.65/ 467
2.28/ 544
133/153
130/144
131/152
134/159
131/148
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Table 4. Graphic representation of HOMO and LUMO orbitals in the studied molecules in
ground and excited state.
Compound
HOMO
LUMO
HOMO – excited state LUMO – excited state
K1
K2
K3
K4
K5
26

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K1
K2
K3
K4
K5
4
2
0
250
300
350
400
450
500
wavelength [nm]
1
,0
K1
K2
K3
K4
K5
0,5
0,0
250
300
350
400
450
500
wavelength [nm]
Figure 6. Experimental (top panel) and TDDFT electronic absorption spectra of the pyrene
derivatives K1ꢀK5.
1
0
,0
,5
K1
K2
K3
K4
K5
0
1
,0
,0
400
450
500
550
600
λ
[nm]
K1
K2
K3
K4
K5
0
0
,5
,0
400
450
500
550
600
wavelength [nm]
Figure 7. Experimental (top panel) and TDDFT fluorescence spectra of the pyrene derivatives
K1ꢀK5.
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0
,8
,6
,4
,2
,0
K6
K7
K8
K9
K10
0
0
0
0
250
300
350
400
450
500
550
K6
K7
K8
K9
K10
wavelength[nm]
1
,2
,0
,8
,6
,4
,2
,0
1
0
0
0
0
0
250
300
350
400
450
500
550
wavelength [nm]
Figure 8. TDDFT (bottom panel) and experimental (top) absorption spectra of the compounds
K6ꢀK10.
1,0
0,8
0,6
0,4
0,2
0,0
K6
K7
K8
K9
K10
400
450
500
550
600
wavelenght [nm]
K6
1,2
1,0
0,8
0,6
0,4
0,2
K7
K8
K9
K10
450
500
550
600
650
wavelenght [nm]
Figure 9. TDDFT (bottom panel) and experimental (top) fluorescence spectra of the
compounds K6ꢀK10. K6 and K8 in bottom panel closely overlap.
28

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Table 5. Molecular parameters derived from (TD)DFT calculations.
Average dihedral angle
Eg (absorption) Eg (Emission) between the central moiety
HOMO
eV]
LUMO (=Eg-
HOMO) [eV]
[
[eV/nm]
[eV/nm]
and the substituents in
ground/excited state [deg]
K6
K7
5.10
4.95
5.09
5.23
5.02
2.32
2.53
2.29
2.14
2.43
2.78/446
2.42/512
2.80/443
3.09/402
2.59/478
2.33/531
2.07/599
2.33/531
2.63/471
2.18/568
150/164
154/162
149/168
150/168
151/162
K8
K9
K10
29