Pyrene derivatives with two types of substituents at positions 1, 3, 6, and 8-fad or necessity?

Article abstract of DOI:10.1039/c9ra04503a

1,3,6,8-Tetrasubstituted pyrene derivatives with two types of substituents in an asymmetry or axial symmetry pattern have been prepared and characterized. To the best of our knowledge, these compounds are compared for the first time to their analogs containing the same substituent at all four positions, which explains the need for their synthesis. We present information on the chemistry of pyrenes, which are substituted in the non-K region, to help obtain the most efficient materials. Moreover, theoretical studies were extended to analogs which contain the first type of substituent at positions 1 and 3, whereas the second type of substituent is located at positions 6 and 8, for which the synthesis is nontrivial. The obtained data show which trend these kinds of molecules will follow.

Full text of DOI:10.1039/c9ra04503a

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PAPER
Pyrene derivatives with two types of substituents at
positions 1, 3, 6, and 8 – fad or necessity?†
Cite this: RSC Adv., 2019, 9, 24015
Dawid Zych *ab and Aneta Slodek
a
1,3,6,8-Tetrasubstituted pyrene derivatives with two types of substituents in an asymmetry or axial
symmetry pattern have been prepared and characterized. To the best of our knowledge, these
compounds are compared for the first time to their analogs containing the same substituent at all four
positions, which explains the need for their synthesis. We present information on the chemistry of
pyrenes, which are substituted in the non-K region, to help obtain the most efficient materials.
Moreover, theoretical studies were extended to analogs which contain the first type of substituent at
positions 1 and 3, whereas the second type of substituent is located at positions 6 and 8, for which the
synthesis is nontrivial. The obtained data show which trend these kinds of molecules will follow.
Received 15th June 2019
Accepted 10th July 2019
DOI: 10.1039/c9ra04503a
rsc.li/rsc-advances
their properties, thereby 1,3-disubstituted pyrene derivatives
are not worth the arduous laboratory work.
Introduction
Pyrene and its derivatives have been the subject of an ever-
Recently in the area of 1,3,6,8-tetrasubstituted pyrenes,
1
increasing number of scientic reports. The purpose of these Zhonghai Ni and co-workers presented novel pyrene derivatives
studies is not only to evolve novel synthetic procedures but also with two different kinds of groups, substituted in a way which
2
10
to investigate the area of potential applications. Pyrene deriva- provides short axial symmetry or asymmetry to the molecules.
tives have become known as excellent candidates for OLED All the compounds contained 4-tert-butylphenyl substituents at
applications because of their uorescence with high quantum positions 1 and 8, whereas at positions 3 and 6 different aryl-
3,4
yields and long lifetimes, but also their thermal stability.
amines were attached: diphenylamine, 4-(diphenylamino)
Various modications of the structure allow obtainment of not phenyl, and 4-(carbazol-9-yl)phenyl. There is no data provided
only blue emitters but also green, yellow, and red depending on about the differences in the properties between 1,3,6,8-tetra-
5
the polarity of the solvent. Moreover, pyrene-fused derivatives substituted pyrene derivatives containing the same incorpo-
are also good candidates for the fabrication of organic solar cell rated group at each of the four positions and those containing
6
devices. The vast majority of pyrene derivatives are 1,3,6,8-tet- two of the above-mentioned substituents at positions 1- and 3-,
rasubstituted by the same group, however, in the area of pyrenes 6- and 8- respectively.
disubstituted at positions 1,6 or 1,8 by the same group, a number
of 1,6-disubstituted derivatives are more signicant.
The same research team published their next article about
a series of short-axial symmetrical and asymmetrical 1,3,6,8-
7,8
We have recently presented theoretical calculations based on tetrasubstituted pyrenes containing two phenyl or 4-methyl-
11
DFT and TD-DFT methods using experimental data for 1,3,6,8- phenyl groups and two diphenylamine groups. It was found
tetrasubstituted pyrenes and 1,6- and 1,8-disubstituted pyrenes that the compounds with substituents providing short axial
9
containing a tetrazole motif with a n-butyl chain. The con- symmetry exhibited higher uorescence quantum yields in
ducted study allowed us to nd the optimal parameters for comparison to the asymmetrically substituted pyrene deriva-
quantum-chemical calculations to predict consistent theoret- tives. Moreover, the asymmetric derivatives were more ther-
ical results for pyrenes substituted at the 1 and 3 position by mally stable.
(hetero)aryl groups, since their synthesis is nontrivial without
What is more, in 2019 Jinchong Xiao et al. presented an
protection of the 7 position. These results showed that the extended 1,3,6,8-tetrasubstituted pyrene derivative which
substitution pattern in disubstituted pyrenes does not inuence contains 4-tert-butylphenyl substituents at positions 1 and 6,
whereas positions 3 and 8 are occupied by 2,7-di-tert-butyl-9,14-
12
diphenyldibenzo[de,qr]tetracene. The obtained compound,
applied in OLEDs, showed exciting properties. Moreover, its
analog containing additional chlorine atoms was used further
a
Institute of Chemistry, Faculty of Mathematics, Physics and Chemistry, University of
Silesia, Szkolna 9, 40-007 Katowice, Poland. E-mail: dawidzych92@gmail.com
b
Institut f u¨ r Silizium-Photovoltaik, Helmholtz-Zentrum Berlin f u¨ r Materialien und in the synthesis of a cyclopenta-embedded arene.
Energie GmbH, Kekul ´e straße 5, 12489 Berlin, Germany
Among the available systematic studies, there is no infor-
mation about comparison of a compound containing two kinds
†
Electronic supplementary information (ESI) available. See DOI:
0.1039/c9ra04503a
1
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of substituents to its exact tetrasubstituted analogs. Further-
more, the 1,3,6,8-tetrasubstituted pyrenes with two types of
substituent groups reported in the literature usually contain
13
amine derivatives as one of the types of unit.
Taking into account the above-described consideration, we
present herein the synthesis and a study of the properties of 1,6-
,
and 1,8-disubstituted and 1,3,6,8-tetrasubstituted pyrenes
containing 4-(2,2-dimethylpropyloxy)pyrid-2-yl and 1-decyl-
,2,3-triazol-4-yl substituents, along with a comparison to and
analysis of the 1,3,6,8-tetrasubstituted analogs with four of the
1
14
same groups which were previously presented by us (Fig. 1).
The experimental study is supported by quantum-chemical
calculations based on DFT and TD-DFT methods. The ob-
tained information should be essential for the development of
materials with excepted properties not only in the area of
organic electronic but also in the area of coordination chem-
istry, where the presented double NCN-cyclometalating pyrenes
15,16
can act as a bridging ligand.
Results and discussion
Synthesis and characterization
Scheme
1
Synthesis of disubstituted pyrene derivatives 8–11.
Reagents and conditions: (a) Br
2
, CCl
4
, room temp., 17 h; (b) TMSA,
$5H O,
ꢀ
[Pd(PPh
3
)
4
], CuI, NEt
3
, 90 C, 16 h; (c) decyl azide, KF, CuSO
4
2
The synthesis routes for disubstituted pyrene derivatives 8–11 sodium ascorbate, pyridine, EtOH, H
2
O, room temp., 24 h; (d) bis(pi-
(dppf)], PhMe, 90 C, 24 h; (e) 2-
ꢀ
nacolato)diboron, KOAc, [PdCl
2
are presented in Scheme 1. The bromination reaction was con-
ducted based on a well-known method which was successfully
bromo-4-(2,2-dimethylpropyloxy)pyridine, K
3
PO
4
$3H
2
O, [Pd(PPh
)
3 4
],
ꢀ
DME, H
2
O, 105 C, 48 h.
17
used previously by us. Pure 1,8- (2) and 1,6-dibromopyrene (3)
were used in Sonogashira coupling reactions, resulting in
disubstituted ethynyl pyrene derivatives protected by a trime-
thylsilyl group (4, 5). Moreover, the dibromopyrenes were also
applied in Suzuki–Miyaura coupling reactions which resulted in
bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)pyrenes (6, 7).
The obtained intermediates were used in the subsequent reac-
tions: 1,3-dipolar cycloaddition or Suzuki–Miyaura coupling,
which were conducted following procedures described by us for
coupling reaction for introduction of the second type of
substituent, we decided to conduct a synthesis of 1,3,6,8-tetra-
substituted pyrene derivatives where the second type of
substituent is introduced using a Sonogashira coupling reac-
tion (Scheme 2). Compound 11 was used as the starting mate-
rial, and the conditions for its bromination were established.
Among the various solvents and brominating agents, dropwise
14
the 1,3,6,8-tetrasubstituted analogs. The target disubstituted
intermediates containing 4-(2,2-dimethylpropyloxy)pyrid-2-yl
ꢀ
addition of bromine to a dichloromethane solution at 40 C was
5
the
most
efficient.
The
obtained
1,6-bis(4-(2,2-
was
(10, 11) or 1-decyl-1,2,3-triazol-4-yl (8, 9) groups at positions 1
dimethylpropyloxy)pyrid-2-yl)-3,8-dibromopyrene 11-Br
2
and 6 or 1 and 8 were obtained with satisfactory 73–92% yields.
Detailed procedures are presented in the ESI.†
used in a Sonogashira coupling reaction with the same reaction
conditions as for the disubstituted pyrenes. However, as a result
of the conducted reaction, the expected product was not ob-
tained. Further modication of 11-Br2 was found to be
nontrivial, and the conditions and reagents of the reaction were
modied; various mixtures of solvents and temperatures were
tried without positive effect. The challenge was solved by adding
12
As opposed to the work of Jinchong Xiao et al., which
included a synthetic route which used a Suzuki–Miyaura
1
eq. of 1,8-diazabicyklo(5.4.0)undek-7-en (DBU) which allowed
obtainment of the pyrene derivative containing two trime-
thylsilyl ethynyl protecting groups and two 4-(2,2-
dimethylpropyloxy)pyrid-2-yl substituents (11-TMSA2). This
intermediate was used in a 1,3-dipolar cycloaddition, which
resulted in the target compound 12 (with 65% yield) containing
two kinds of substituents, with the substituent pattern
providing asymmetry to the molecule.
The same synthetic route was applied for 10, which allowed
obtainment of the pyrene derivative with short axial symmetry
Fig. 1 Tetrasubstituted pyrene derivatives with one or two types of
substituent.
(13) with a yield of 75% expressed per the starting material. The
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ꢀ
2 2 3 4
Cl , 40 C, 2 h; (b) TMSA, [Pd(PPh ) ], CuI,
Scheme 2 Synthesis of tetrasubstituted pyrene derivative 12. Reagents and conditions: (a) Br
2
, CH
O, room temp., 24 h.
ꢀ
NEt
3
, DBU, 90 C, 16 h; (c) decyl azide, KF, CuSO
4
2
$5H O, sodium ascorbate, pyridine, EtOH, H
2
1
13
ꢀ
– the 1,8-disubstituted pyrenes – and equal 375 C. In the case of
structures of compounds 4–13 were conrmed using H and
C
NMR, and, for 8–13, using mass spectrometry. The spectra are tetrasubstituted pyrenes 12 and 13, the decomposition
presented in the ESI as Fig. S7–S24.†
temperature is signicantly lower for 12, which contains the
same type of substituent at positions 1,6 and 3,8, respectively.
This shows the tendency for two substituents on the one side of
the pyrene to increase the thermal stability of the obtained
Thermal properties
The obtained compounds 8–13 were examined in terms of their molecules, which is in opposition to the observation of
11
thermal properties by using thermogravimetric analysis (TGA) Zhonghai Ni and co-workers. Moreover, comparing the
ꢀ
with a temperature range up to 900 C under a nitrogen atmo- thermal stability of disubstituted pyrenes 8–9 and 10–11, which
sphere. The obtained data curves are presented in Fig. 2a and b, contain pyridyl and triazolyl substituents, with the already re-
whereas the temperatures corresponding to 5 and 10% weight ported by us disubstituted pyrenes with tetrazolyl groups,
loss during heating and the values for the char residue and a signicant difference in thermal stability can be observed. The
temperature of maximal decomposition are presented in Table 1. temperature for 5% weight loss for the compounds with tetra-
ꢀ
9
Analysis of the presented data showed that within the range zolyl groups is lower by at least 62 C. Taking into account the
of the studied group of compounds, disubstituted pyrenes are tetrasubstituted pyrenes containing the same four substituents
more thermally stable than tetrasubstituted pyrenes; the published previously by us, it can be observed that the
temperatures of 5% decomposition are the highest for 8 and 10 temperatures of T5% for 12 and 13 are located between the
corresponding temperatures of the pyrenes with the same four
1
4
ꢀ
substituents. Moreover, the char residue at 900 C values for
the disubstituted pyrenes are signicantly lower than for the
tetrasubstituted pyrenes with either four identical substituents
or two kinds of substituents, whereas, among the group of tet-
rasubstituted pyrenes, the char residue values for 12 and 13 are
higher than for the analogs containing all of the same
substituents.
Theoretical studies
In order to gain a deep insight into the structure of the obtained
compounds, theoretical calculations based on the DFT method
a,b
Table 1 Thermal properties of the molecules 8–13
TGA
Char residue
at 900 C [%]
ꢀ
ꢀ
ꢀ
ꢀ
T
5% [ C]
T
10% [ C]
T
max [ C]
8
9
1
1
1
1
375
324
375
358
255
319
385
357
387
378
300
379
411
414
414
432
274, 439
423
4
1
9
2
27
34
0
1
2
3
a
T
5%, T10% – the temperature corresponding to 5% and 10% weight
b
loss.
Tmax – the maximum decomposition temperature from the
Fig. 2 TGA (a) and DTG (b) curves for 8–13.
DTG thermograms.
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were performed. Based on previous experience, the structural
Paper
18
In the case of disubstituted pyrenes 8–11, the values of the
investigations were conducted using the B3LYP exchange- energy gaps for the 1,6-isomers are slightly higher in compar-
9
correlation functional with basis set 6-31G(d,p). The opti- ison to the 1,8-isomers. The energy gaps of 12 and 13 are the
mized structures (top and side views), energies and contours for same and equal 3.19 eV, and this value of the energy gap is
the frontier orbitals with the contributions to their creation, between the values for analogous tetrasubstituted pyrenes with
14
and the values of the energy gaps, for molecules 8–13 are pre- the same four substituents. The substitution pattern does not
sented in Table 2. inuence the value of the energy gap. Moreover, the
Table 2 The optimized structures (6-31G(d,p)/B3LYP) 8–13, energies and contours for the HOMOs and LUMOs with the contributions to their
creation for compounds 8–11 (pyrene/heteroaryl) and 12–13 (pyrene/pyridyl/triazolyl)
Top view
Side view
HOMO
LUMO
DE [eV]
8
9
3.43
ꢁ
5.27
0/20
ꢁ1.84
8
84/16
3.45
ꢁ
5.28
1/19
ꢁ1.83
8
85/15
1
0
3.45
ꢁ
5.32
6/14
ꢁ1.87
8
79/21
1
1
3.49
3.19
ꢁ
5.35
7/13
ꢁ1.86
8
80/20
1
2
5
7
.23
5/9/16
ꢁ2.04
74/14/12
1
3
3.19
ꢁ
5.21
5/10/15
ꢁ2.02
7
74/15/11
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contribution of a particular part of the studied compounds to Table 4 The angles between the pyrene and pyridyl/triazolyl substit-
uent in molecules 8–13
the creation of orbitals HOMO-2, HOMO-1, HOMO, LUMO,
LUMO+1, and LUMO+2 was determined and the results are
presented in the ESI (Table S1†). The HOMOs of 8 and 9 are
created with a higher contribution from the heteroaryl substit-
uents – triazolyl groups (z20%) – compared to 10 and 11 –
pyridyl units (z14%) – which also translates into creation of the
LUMOs, which is the opposite. The contributions from the
substituents in the creation of the selected orbitals for 12 and 13
show that the frontier orbitals do not differ from each other, but
signicant differences are observed for HOMO-2, HOMO-1,
LUMO+1, and LUMO+2 – orbitals which are very important in
determination of the optical properties (described in detail in
the paragraph on optical properties). The contribution from the
heteroaryl groups in the creation of the orbitals mentioned
above is much higher for 13, which contains the rst type of
substituent at positions 1 and 8 whereas the second kind is
located at positions 3 and 6. The differences between
compounds 12 and 13 and their already reported analogs P1
ꢀ
Angle [ ]
Ground state
Pyridyl
Excited state
Pyridyl
Triazolyl
Triazolyl
8
9
1
1
1
1
—
—
44.58
48.60
47.60
46.59
34.09
38.52
—
—
36.18
35.77
—
—
34.20
37.79
39.51
38.99
24.14
26.09
—
—
28.26
27.35
0
1
2
3
ꢀ
between the angles of the 1,6- and 1,8-isomers is about 4 , and
in comparison, the value for the disubstituted pyrene with tet-
razolyl groups was much lower; the value for the equivalent
measurement was about 12 with also lower values for the
angles of the respective isomers. In the case of compound 13,
ꢀ
9
14
and P4 containing the same four substituents were also
checked by extension of this research to calculate the contri-
butions to the creation of the same orbitals as for 12 and 13. The
results are presented in Table 3 and in the ESI in Table S2.†
The contribution from the pyridyl in the creation of the
frontier orbitals is much higher than for the triazolyl unit. The
sum of the contributions from the heteroaryl groups for the
HOMO and LUMO for molecules 12 and 13 is 26 and 25%,
respectively. The frontier orbitals in the case of P1 are created by
the angles between the pyrene and the pyridyl and triazolyl
groups are lower in comparison to molecule 12, but all the angle
ꢀ
14
values are higher than for P1 and P4 by up to 3 . For all the
studied compounds, the angles in the excited state are lower by
ꢀ
up to 12 than in the ground state.
Optical properties and TD-DFT study
The absorption and emission spectra of pyrene derivatives 8–13
were obtained from CH Cl solutions and the solid state. The
2 2
obtained data are presented in Fig. 3 and 4, Table 5, and also in
the ESI in Fig. S1–S6.†
46% (HOMO) and 48% (LUMO) contributions from the pyridyl,
and in the case of P4 by 28 and 24% contributions from the
triazolyl, respectively.
What is more, the other structural parameters – the angles
between the pyrene core and the substituents – were calculated
for the ground and excited states. The values for the angles are
presented in Table 4.
The angle between the plane of the pyrene and the substit-
uents for disubstituted pyrenes is higher for compounds with
pyridyl groups and higher for the 1,6-isomer. The difference
The absorption spectra of 8 and 9 with the same substituents
but linked to the pyrene at different positions are identical to
those of compounds 10 and 11 (Fig. 3). The same phenomenon
was observed for the 1,8- and 1,6-disubstituted pyrenes with
tetrazole, thiophene, and furan substituents, disclosing that the
substitution positions (1,8- or 1,6-) do not inuence the elec-
9,19
tronic transitions.
Comparing compounds 8 and 9 with 10
and 11, a small red shi of the absorption maxima was
observed, ca. 7 nm, which could be attributed to the slightly
stronger donating ability of the triazolyl substituents of 8 and 9.
Table 3 Contours for the frontier orbitals with the contributions to
their creation for compounds P1 and P4 (pyrene/heteroaryl)
HOMO
LUMO
DE [eV]
P1
P4
3.22
ꢁ
5.36
4/46
ꢁ2.14
5
52/48
3.16
ꢁ
5.22
2/28
ꢁ2.06
Fig. 3 Absorption spectra recorded for 8–13 in a CH Cl solution (c ¼
2
2
ꢁ
5
ꢁ1
7
76/24
10 mol L ).
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transitions. In the case of 12 and 13, the substitution pattern
did not inuence the position of the absorption peaks. TD-DFT
calculations with B3LYP and CAM-B3LYP exchange-correlation
functionals were performed for compounds 8–13. The spectral
matching is much better for the results of the calculations using
the B3LYP functional, especially in the area of high energy
transitions; a comparison of the results is presented in the ESI
(Table S3†). The results demonstrate that the calculated elec-
tron transitions related to the absorption bands are adequately
correlated to the experimental ones and follow the same
substitution pattern trend (Table 6).
The results show that among the pyrene derivatives with two
substituents 8–11, 1,8-disubstituted pyrenes (8 and 10) display
a weaker strength of oscillator (f ¼ 0.70) than the 1,6-disubsti-
tuted pyrenes 9 and 11 (f ¼ 0.87) for the rst transition (HOMO
/
LUMO), whereas the tetrasubstituted compounds 12 and 13
possess a similar strength of oscillator of 0.87 (Table 6).
Moreover, the absorptions of 12 and 13 were also analyzed
using Natural Transition Orbitals (NTOs), and the results for 12
are presented in Table 7 (for 13, see the ESI, Table S4†). The hole
(HOTO)/electron (LUTO) pairs show the nature and the number
of excited states which are involved in the absorption, which in
the case of molecule 13 are greater than for 12. This conrmed
that most of the absorption bands are dominated by excited
states in which the HOTO is localized on the pyrene with a low
contribution from the substituents. A signicant contribution
to the HOTOs can be observed partially for excited states S , S
Fig. 4 Emission spectra recorded from (a) a CH
2
Cl
2
solution (c ¼
ꢁ5
ꢁ1
1
0
mol L ) and (b) the solid state for 8–13.
1
9
22,
and S , where the participation of the triazolyl groups is higher
2
5
than of the pyridyl units. These excited states are involved in the
creation of the lowest energy bands. In the case of 13, its
absorption is characterized by a higher number of excited
states, and a signicant contribution from the substituent
The compounds with four groups attached, 12 and 13, exhibited
strong red-shied absorption maxima, ca. 25 nm, in relation to
the compounds with two substituents 8, 9, 10 and 11, indicating
that the additional substituents strongly affect the electronic
Table 5 Photophysical and optical data recorded for 8–13
PL lem [nm]/Stokes
ꢁ1
a
2
6 b ꢁ1
6 b ꢁ1
opt c
g
lmax [nm]
lex [nm]
shi [cm
]
F [%] s [ns] (weight %)
c
k
r
$10 [s
]
k
nr$10 [s
]
E
[eV]
8
9
1
1
Solution 277, 287, 365 254, 288, 365
403/2584, 421/3645 63.84 3.72 [0.04 (12.37)
.24 (87.63)]
4
171.61
97.20
3.09
4
Powder
—
284, 326, 364
493/7189
—
—
—
—
—
154.56
2.52
3.08
Solution 277, 286, 367 254, 286, 364
403/2434, 423/3607 63.37 2.37 [0.03 (18.07) 1.023 267.38
.89 (81.93)]
2
Powder
—
276, 326, 366
483/6619
405/3164
—
—
—
—
—
231.29
2.57
3.06
0
1
Solution 276, 286, 359 254, 286, 360
66.00 1.47 [0.03 (18.50) 1.145 448.98
.78 (87.10)]
1
Powder
—
278, 322, 366, 416 452/5199
—
—
—
—
—
272.14
2.74
3.07
Solution 275, 285, 359 252, 286, 362
404/3103
64.35 1.31 [0.04 (24.71) 1.073 491.22
.73 (75.29)]
1
Powder
—
274, 310, 402
459/3089
437/2758
508/2837
438/2810
—
—
—
—
—
55.56
—
2.70
2.84
2.44
2.83
1
2
3
Solution 255, 298, 390 258, 302, 376
89.00 1.98
—
94.83 1.69 [0.04 (19.10) 1.091 561.12
2.08 (80.90)]
1.053 449.49
—
Powder
Solution 259, 285,
97, 390
—
280, 336, 444
260, 302, 380
—
—
1
30.59
2
Powder
—
284, 368, 426
516/4095, 542/5024
—
—
—
—
—
2.40
a
b
Absolute quantum yields obtained using an integrating sphere in optically diluted dichloromethane solutions at 298 K. Radiative (k
r
) and non-
radiative (knr) decay rates, assuming that the emission excited states are produced with unit efficiency, were estimated using the following
c
opt
g
equations: k
r
¼ Fem/s; knr ¼ (1 ꢁ Fem)/s.
E
¼ 1241/lem
.
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ꢁ1
5
groups was also observed partially for S . This can also prove shis in the range of 2434 to 3645 cm (Table 5) because their
that the intensity of the absorption in the high energy area of 13, geometry in the excited state becomes more planar compared to
in comparison to 12, is signicantly higher. the twisted conformation in the ground state (Table 4).
The uorescence emission maxima for 8–13 in CH Cl2 Furthermore, the substituents in 8 and 9 have the smallest twist
2
solutions are located between 403 and 438 nm (ESI, Fig. S1†) angles relative to the pyrene molecule, reecting the highest
and maintain the same trend depending on the substitution values for the Stokes shis for 8 and 9.
pattern relative to their absorption spectra. Compounds 10–13
show a single emission with a maximum at 405 nm for 10 and cence quantum yields (F), found to be ca. 66%, while
1, and at ca. 380 nm for 12 and 13, whereas compounds 8–9 compounds 12 and 13 exhibit higher F values ca. 90%. The
possess a primary emission at 403 nm and a shoulder peak at higher F values of 12 and 13 with respect to P1 (F ¼ 72%) and
The disubstituted pyrenes 8–11 show comparable uores-
1
4
22 nm. The emission wavelengths for 8–13 in CH Cl as P4 (F ¼ 77%), the compounds containing the same four
2
2
14
calculated using TD-DFT with CAM-B3LYP are red-shied for 12 groups that were reported previously, in addition to the
and 13 (ca. 40 nm) compared to 8–11, similar to the experi- slight difference in the F value for 13 in comparison to 12 (by
mental data (Table 8).
5%), imply that variation of the substituents at positions 1, 3, 6
The 1,8-disubstituted pyrenes 8 and 10 possess similar and 8 plays an important role. Compound 13 exhibiting
oscillator strengths, but lower than for the 1,6-disubstituted a higher uorescence quantum yield has a substitution
pyrenes 9 and 11. The emission bands for all the studied pattern that provides short axial symmetry, in which the
compounds occur from HOMO / LUMO transitions, with 98% substituent groups are twisted by lesser angles in relation to
contribution. The examined compounds exhibit large Stokes the pyrene compared to molecule 12. This phenomenon is also
Table 6 Results from calculated absorption spectra using a TD-DFT method (6-31G(d,p)/B3LYP) with the oscillator strengths for 8–13
Exp.
365
Calculated
Transitions (contribution)
8
390.26 (0.6990)
296.34 (0.5497)
HOMO / LUMO (97%)
287
H-2 / LUMO (10%), H-1 / LUMO (45%), HOMO / L+1 (39%)
H-2 / LUMO (45%), HOMO / L+3 (29%), HOMO / L+5 (13%)
H-6 / LUMO (11%), H-4 / LUMO (10%), H-1 / L+1 (60%)
H-2 / L+1 (42%), H-1 / L+3 (14%), H-1 / L+5 (17%),
HOMO / L+6 (15%)
2
78.50 (0.1282)
242.00 (0.3775)
34.12 (0.1182)
277
2
9
1
367
388.60 (0.8630)
287.25 (0.4442)
253.36 (0.1520)
HOMO / LUMO (97%)
2
2
86
77
H-1 / LUMO (50%), HOMO / L+1 (44%)
H-4 / LUMO (82%), H-1 / L+1 (15%)
H-6 / LUMO (88%)
H-4 / LUMO (13%), H-1 / L+1 (65%)
HOMO / LUMO (97%)
H-1 / LUMO (17%), HOMO / L+1 (48%), HOMO / L+2 (29%)
H-2 / LUMO (16%), H-1 / LUMO (21%), HOMO / L+2 (39%)
H-8 / LUMO (53%), H-1 / L+1 (21%), HOMO / L+6 (16%)
H-1 / L+1 (15%), H-1 / L+2 (14%), H-1 / L+4 (16%)
H-7 / L+3 (10%), H-1 / L+1 (17%), H-1 / L+2 (15%),
H-1 / L+4 (10%)
2
2
47.29 (0.1185)
36.72 (0.7401)
0
359
390.17 (0.7049)
300.23 (0.4483)
286
290.57 (0.2200)
276
260.02 (0.1666)
2
2
37.61 (0.1765)
36.44 (0.2512)
1
1
2
359
386.67 (0.8709)
287.41 (0.4461)
255.01 (0.2043)
HOMO / LUMO (96%)
2
2
85
75
H-1 / LUMO (40%), HOMO / L+1 (50%)
H-8 / LUMO (77%), H-1 / L+1 (16%)
H-1 / L+1 (60%)
H-7 / L+2 (19%), H-2 / L+2 (21%), H-1 / L+4 (12%)
HOMO / LUMO (98%)
H-1 / LUMO (37%), HOMO / L+1 (55%)
H-10 / LUMO (80%), H-1 / L+1 (15%)
H-12 / LUMO (50%), H-10 / LUMO (13%), H-1 / L+1 (33%)
H-12 / LUMO (40%), H-1 / L+1 (37%)
H-7 / L+2 (15%), H-6 / L+1 (10%), H-2 / L+2 (17%),
H-1 / L+4 (14%)
2
2
36.89 (0.5277)
34.07 (0.2267)
1
390
425.38 (0.8613)
310.17 (0.9540)
258.59 (0.1066)
2
2
98
55
255.34 (0.2176)
244.25 (0.2474)
238.16 (0.1066)
1
3
390
426.15 (0.8701)
316.09 (0.5977)
303.33 (0.2731)
259.10 (0.1843)
HOMO / LUMO (98%)
297
285
259
H-1 / LUMO (23%), HOMO / L+1 (48%), HOMO / L+2 (16%)
H-2 / LUMO (26%), H-1 / LUMO (11%), HOMO / L+2 (40%)
H-10 / LUMO (38%), H-1 / L+1 (44%)
H-12 / LUMO (28%), H-1 / L+2 (62%)
HOMO / L+9 (85%)
251.72 (0.1277)
248.06 (0.1313)
244.63 (0.2994)
H-12 / LUMO (37%), H-1 / L+1 (27%), H-1 / L+2 (14%)
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Table 7 Natural transition orbitals (NTOs) with occupied (holes) and unoccupied (electrons) pairs with a contribution higher than 25% for 12,
presenting the nature of the absorption spectrum (6-31G(d,p)/B3LYP) with the contributions from the (pyrene/pyridyl/triazolyl) substituents. For
each state, the respective values for the state, transition energy, and oscillator strength are listed
Exp.
Hole (HOTO)
Electron (LUTO)
3
90 nm
S
S
1
, 2.915 eV (0.861), 98%
, 3.997 eV (0.954), 55%
0
0
0
0
0
0
0
.79/0.08/0.13
.79/0.08/0.13
.55/0.19/0.26
.06/0.43/0.51
.08/0.37/0.54
.76/0.09/0.14
.18/0.27/0.55
0.78/0.10/0.12
0.88/0.07/0.05
0.78/0.10/0.12
0.78/0.10/0.12
0.78/0.10/0.12
0.88/0.07/0.05
0.78/0.10/0.12
4
2
98 nm
S
S
S
S
S
4
, 3.997 eV (0.954), 40%
19, 4.795 eV (0.107), 80%
22, 4.856 eV (0.218), 63%
22, 4.856 eV (0.218), 33%
25, 5.076 eV (0.247), 43%
2
55 nm
S
25, 5.076 eV (0.247), 37%
0.76/0.09/0.14
0.88/0.07/0.05
supported by the trend in the calculated dipole moment (m),
Unlike with compound 12, where the uorescence decays
which for 13 is higher than for 12 (Table 9), and is directly become monoexponential, the remaining compounds exhibited
related to the symmetry of 13, and is also reected in the a bi-exponential tted decay curve. The average lifetimes of 8–13
higher emission and absorption intensities (Fig. 3 and 4). are comparable and are in the range of 1.31–3.72 ns (Table 5).
Moreover, the improvement in the F values of 12 and 13 All of the pyrene derivatives display luminescence in the solid
relative to 8–11 correlates to the four substituents on the state with structure-less uorescence maxima in the range of
pyrene molecule that elongate the conjugation length and 452–542 nm (Fig. 4b). In the solid state, the emission maxima of
expand the p-delocalization.
8–13 are signicantly red-shied, even by ca. 100 nm, with
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Table 8 Calculated using TD-DFT (6-31G(d,p)/CAM-B3LYP) wavelengths of emission with the oscillator strengths for 8–13
Calculated wavelength [nm] (oscillator strength)
429.76 (1.0282)
Transitions
8
9
1
1
1
1
HOMO / LUMO (98%)
H-1 / LUMO (46%), HOMO / L+1 (44%)
HOMO / LUMO (98%)
HOMO / L+1 (50%), H-1 / LUMO (46%)
HOMO / LUMO (98%)
H-1 / LUMO (53%), HOMO / L+1 (23%), HOMO / L+2 (14%)
HOMO / LUMO (98%)
H-1 / LUMO (56%), HOMO / L+2 (38%)
HOMO / LUMO (98%)
H-1 / LUMO (58%), HOMO / L+1 (34%)
HOMO / LUMO (98%)
3
38.53 (0.0097)
431.41 (1.2497)
36.19 (0.0008)
434.99 (1.0793)
39.34 (0.0231)
434.86 (1.3332)
36.97 (0.0144)
470.76 (1.1944)
52.10 (0.0637)
473.33 (1.1940)
53.25 (0.0614)
3
0
1
2
3
3
3
3
3
H-1 / LUMO (58%), HOMO / L+1 (26%)
respect to those for the compounds in solution, which is
Table 9 Calculated dipole moments (B3LYP/6-31G**) for molecules probably caused by strong intermolecular p–p aggregation. The
1
2 and 13
emission spectra of 8 and 9 are broad and the maxima are sit-
uated at 493 and 483 nm, respectively, with vanishing of the ne
structures of the spectra. The shape and signicant shi of the
emission by 70 nm for 8 and 9 in the solid state are most likely
due to more planar molecular conformations caused by the
facile formation of strong intermolecular interactions between
Ground state
) [D]
(
m
g
e
Excited state (m ) [D]
20,21
1
2
3
the pyrene units.
However, compounds 10 and 11 containing
the sterically bulky 2,2-dimethylpropyloxy groups, which affect
the stacking arrangement of the molecules in the solid state,
exhibit the smallest red-shi of the emission peaks, ca. 45 nm.
In the case of the solid state spectra for 12 and 13 (in relation to
the analogous spectra for the compounds in solution),
a comparable bathochromic shi of ca. 80 nm in the emission
spectra appeared, which reveals that in both compounds, in the
solid state, intermolecular p–p aggregation is present.
1
3
.10
.18
1.13
1
3.77
Two kinds of substituents at positions 1, 3 and 6, 8,
respectively – theoretical considerations
9
The presented results and our previous study conrm that
substitution at the 1,3-, 1,6- or 1,8- positions of the pyrene core
does not provoke any changes in the photophysical properties,
whereas tetrasubstituted molecules with two kinds of substit-
uent groups at positions 1, 3, 6 and 8 cause changes in the
optical features. This inspired us to conduct a theoretical
investigation of the molecule (14) which contains the rst type
of substituent at positions 1 and 3, whereas the second type of
Fig. 5 Compound 14 containing the first type of substituent at posi-
tions 1 and 3, and the second type at positions 6 and 8.
Table 10 Contours for selected orbitals with the contributions to their creation for compound 14 (pyrene/pyridyl/triazolyl)
HOMO
LUMO
DE [eV]
1
4
3.19
ꢁ
5.21
5/10/15
ꢁ2.02
7
74/15/11
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substituent is located at positions 6 and 8 (Fig. 5). The detailed
data are presented in Table 10 and the ESI (Tables S5–S9†).
Comparing the localization of the orbitals of 14, which
determine the optical properties, to the corresponding orbitals
of 12 and 13, did not show any differences, and the value for the
energy gap is 3.19 eV. The angles between the substituents for
the optimized structure are lower in comparison to molecules
3 J. Yang, L. Li, Y. Yu, Z. Ren, Q. Peng, S. Ye, Q. Li and Z. Li,
Mater. Chem. Front., 2017, 1, 91–99.
4 M. Fang, J. Huang, Y. Zhang, X. Guo, X. Zhang, C.-F. Liu,
W.-Y. Lai and W. Huang, Mater. Chem. Front., 2017, 1, 668–676.
5 Y. Niko, S. Sasaki, K. Narushima, D. K. Sharma, M. Vacha
and G.-I. Konishi, J. Org. Chem., 2015, 80, 10794–10805.
6 Y. Gong, K. Chang, C. Chen, M. Han, X. Zhan, J. Min, X. Jiao,
Q. Li and Z. Li, Mater. Chem. Front., 2019, 3, 93–102.
7 R. K. Konidena, K. R. Justin Thomas, M. Singh and J.-H. Jou,
J. Mater. Chem. C, 2016, 4, 4246–4258.
12 and 13, which can reveal that molecule 14 would exhibit
a higher quantum yield. Moreover, the results of the TD-DFT
calculations revealed that in the case of calculated absorption
spectra, the number of high energy absorption bands for 14 is
lower than for 12 and 13, whereas the emission spectra did not
differ to each other.
8 M. Jung, J. Lee, H. Jung, S. Kang, A. Wakamiya and J. Park,
Dyes Pigm., 2018, 158, 42–49.
9 D. Zych, A. Slodek and A. Frankowska, Comput. Mater. Sci.,
2
019, 165, 101–113.
0 R. Zhang, Y. Zhao, T. Zhang, L. Xu and Z. Ni, Dyes Pigm.,
016, 130, 106–115.
1
Experimental
2
Detailed information about the materials, methods, and 11 R. Zhang, T. Zhang, L. Xu, F. Han, Y. Zhao and Z. Ni, J. Mol.
synthesis of 8–13 is presented in the ESI.†
Struct., 2017, 1127, 237–246.
1
1
2 X. Liu, F. Tian, Y. Han, T. Song, X. Zhao and J. Xiao, Dyes
Pigm., 2019, 167, 22–28.
3 X. Feng, H. Tomiyasu, J.-Y. Hu, X. Wei, C. Redshaw,
M. R. J. Elsegood, L. Horsburgh, S. J. Teat and T. Yamato,
J. Org. Chem., 2015, 80, 10973–10978.
Conclusions
In conclusion, effective synthetic routes for the synthesis of
1,3,6,8-tetrasubstituted pyrene derivatives containing two kinds
of substituent groups, providing short axial symmetry or 14 D. Zych, A. Kurpanik, A. Slodek, A. Maro n´ , M. Paj ˛a k,
asymmetry, were developed. Furthermore, the conducted pho-
tophysical studies and theoretical calculations, when compared
to data for analogs with the same four substituents, exposed the
G. Szafraniec-Gorol, M. Matussek, S. Krompiec, E. Schab-
Balcerzak, S. Kotowicz, M. Siwy, K. Smolarek, S. Ma ´c kowski
and W. Danikiewicz, Chem.–Eur. J., 2017, 23, 15746–15758.
legitimacy of research dedicated to the compounds with two 15 D. Zych, A. Slodek, D. Matuszczyk and S. Golba, Eur. J. Inorg.
kinds of substituent units, especially the compounds with Chem., 2018, 47, 5117–5128.
a substitution pattern that provides axial symmetry (13), which 16 D. Zych, A. Slodek, S. Golba and S. Krompiec, Eur. J. Inorg.
determines more efficient uorescence. Moreover, the theoret- Chem., 2018, 14, 1581–1588.
ical study of the analog for which the synthesis is nontrivial 17 J. Grimshaw and J. Trocha-Grimshaw, J. Chem. Soc., Perkin
showed that compounds with this kind of substitution pattern Trans. 1, 1972, 1622.
would follow the trend of derivatives with short axial symmetry. 18 M. J. Frisch, G. Trucks, H. Schlegel, G. Scuseria, M. Robb,
The results also showed that the examined compounds exhibit
interesting properties which can predestine them as potential
materials for organic electronics, which will be the subject of
our further investigations.
J. Cheeseman, G. Scalmani, V. Barone, B. Mennucci,
G. Petersson, H. Nakatsuji, M. Caricato, X. Li, H. Hratchian,
A. Izmaylov, J. Bloino, G. Zheng, J. Sonnenberg, M. Hada,
M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida,
T. Nakajima, Y. Honda, O. Kitao, H. Nakai, T. Vreven,
J. Montgomery, J. Peralta, F. Ogliaro, M. Bearpark, J. Heyd,
E. Brothers, K. Kudin, V. Staroverov, R. Kobayashi,
J. Normand, K. Raghavachari, A. Rendell, J. Burant,
S. Iyengar, J. Tomasi, M. Cossi, N. Rega, J. Millam, M. Klene,
J. Knox, J. Cross, V. Bakken, C. Adamo, J. Jaramillo,
R. Gomperts, R. Stratmann, O. Yazyev, A. Austin, R. Cammi,
C. Pomelli, J. Ochterski, R. Martin, K. Morokuma,
V. Zakrzewski, G. Voth, P. Salvador, J. Dannenberg,
S. Dapprich, A. Daniels, O. Farkas, J. Foresman, J. Ortiz,
J. Cioslowski and D. Fox, Gaussian 09, Revis. B.01, Gaussian,
Inc., Wallingford CT.
Conflicts of interest
There are no conicts to declare.
Acknowledgements
This work was supported by the Ministry of Science and Higher
Education, Poland Diamentowy Grant number 0215/DIA/2015/
44. D. Zych was nanced by the National Science Centre of
Poland, ETIUDA 6 2018/28/T/ST5/00005. Calculations were
carried out using resources provided by Wroclaw Centre for
Networking and Supercomputing (http://wcss.pl), Grant no. 18. 19 K. R. Idzik, P. J. Cywi n´ ski, W. Kuznik, J. Frydel, T. Licha and
T. Ratajczyk, Phys. Chem. Chem. Phys., 2015, 17, 22758–
2
2769.
Notes and references
2
0 R. Nandy, M. Subramoni, B. Varghese and S. Sankararaman,
1
2
D. Zych, Molecules, 2019, 24, 2551.
M. M. Islam, Z. Hu, Q. Wang, C. Redshaw and X. Feng, Mater. 21 Z. Zhao, X. Xu, Z. Jiang, P. Lu, G. Yu and Y. Liu, J. Org. Chem.,
Chem. Front., 2019, 3, 762–781. 2007, 72, 8345–8353.
J. Org. Chem., 2007, 72, 938–944.
24024 | RSC Adv., 2019, 9, 24015–24024
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