Branched oligophenylenes containing octylphenotiazine and dioctylfluorene groups and phen-1,3,5-triyl branching center

Article abstract of DOI:10.1007/s11172-018-2236-y

A series of branched oligophenylenes containing the dioctylfluorene and octylphenothiazine moieties was synthesized using the Suzuki reaction applied within the framework of the A₂ + B₂ + B₃ approach. 1,3,5-tris(7-Bromo-9,9-di-n-octylfluoren-2-yl)benzene and 1,3,5-tris- (4-bromophenyl)benzene were used as the branching co-monomers. It was shown that the fluorescence spectra of co-oligomers containing phenothiazine moieties are shifted to the longwavelength region as compared to the spectra of that without such moieties.

Full text of DOI:10.1007/s11172-018-2236-y

Russian Chemical Bulletin, International Edition, Vol. 67, No. 8, pp. 1433—1439, August, 2018
1433
Branched oligophenylenes containing octylphenotiazine and dioctylfluorene
groups and phen-1,3,5-triyl branching center
A. I. Kovalev, E. S. Martyanova, M. N. Sycheva, I. B. Suntsova,
N. S. Kushakova, I. A. Abramov, and I. A. Khotina
A. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences,
2
8 ul. Vavilova, 119991 Moscow, Russian Federation.
Fax: +7 (499) 135 6549. E-mail: khotina@ineos.ac.ru
A series of branched oligophenylenes containing the dioctylfluorene and octylphenothiazine
moieties was synthesized using the Suzuki reaction applied within the framework of the
A + B + B approach. 1,3,5-tris(7-Bromo-9,9-di-n-octylfluoren-2-yl)benzene and 1,3,5-tris-
2
2
3
(
4-bromophenyl)benzene were used as the branching co-monomers. It was shown that the
fluorescence spectra of co-oligomers containing phenothiazine moieties are shifted to the long-
wavelength region as compared to the spectra of that without such moieties.
Key words: branched oligophenylenes, Suzuki reaction, phenothiazine moieties, 1,3,5-tri-
phenylbenzene, 1,3,5-tris(9,9-di-n-octylfluorene-2,7-ylene)benzene.
Electroluminescent polymers became applied as mater-
among the available heterocyclic compounds containing
electron-rich sulfur and nitrogen heteroatoms. Polymers
ials for the active layers of light-emitting diodes (PLED).
A significant interest of researchers is attracted by the op-
portunity of employing these polymers in flat panel dis-
plays and illuminating devices.1
2
0,21
and organic molecules
possessing moieties of pheno-
thiazine or its derivatives have recently attracted an atten-
tion of researchers due to the unique optoelectronic
properties that make these compounds being promising
—4
The introduction of molecular functional moieties,
including chromophoric ones, into polymers allows one
to modify their structure and create new materials that
8
materials for applications in light-emitting diodes, photo-
1
7,18
voltaic, and chemiluminescent devices.
It was assumed
5
possess, e.g., an adjustable fluorescence.
that the inclusion of phenothiazine or its derivatives in the
PF chain should improve the hole conductivity and thus
Polyfluorene (PF)6
—10
and its derivatives are of par-
1
2,22
ticular interest among the photo- and electro-active con-
jugated polymers, since they can be successfully applied
in PLED due to the high quantum efficiency of photo-
luminescence (PL), a good thermal stability, and the
opportunity to introduce various functional groups at the
position 9 of fluorene.
increase the electroluminescence efficiency.
More-
over, the nonplanar structure of the phenothiazine ring is
1
2
capable of the aggregation inhibition. The electron-rich
phenothiazine ring is an excellent molecular building block
to achieve the better emission and also hole conductivity
in polymer electronic devices.
A series of polyfluorenes was previously synthesized
via the introduction of units of various modifying como-
nomers into the polymer chain. Investigations of the
Taking into account the facts mentioned above, it was
interesting to synthesize new fluorescent oligomers with
a branched structure containing the fluorene, pheno-
thiazine, and phenylene moieties. The Suzuki reaction was
employed for the synthesis of soluble branched oligomers
opportunity to prepare highly-efficient red, green, and blue
photoemitters based on them1
1—13
confirmed the applica-
tion perspectiveness of these polymers in PLED.
via a polycondensation of А + В + В type.
2 2 3
A covalent attachment of the chromophore to the
polymer is the most widely used one among various meth-
ods for adjusting the color of LED, since this approach
prevents the formation of aggregates. In the case of two
chromophores mixed, the energy transfer occurs from the
dye with a larger band-gap to the dye with the narrower
Results and Discussion
In the present work, branched co-oligomers containing
phenylene, fluorene, and also phenothiazine moieties were
synthesized, and a primary analysis of their luminescent
properties was carried out. At the first stage, the bi-
functional monomer 3,7-dibromo-10-n-octylphenothi-
azine (1) was obtained. It was prepared via the two-step
1
4,15
band, and the emission from the latter is prevalent.
Chromophore fragments such as thiophene, bithiophene,
benzothiazole, and benzodithiazole derivatives are cur-
rently applied for this purpose.1
6—19
Phenothiazine is one
method (Scheme 1).
23
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1433—1439, August, 2018.
066-5285/18/6708-1433 © 2018 Springer Science+Business Media, Inc.
1

1434
Russ. Chem. Bull., Int. Ed., Vol. 67, No. 8, August, 2018
Kovalev et al.
Scheme 1
The octyl moiety was initially attached to phenothi-
Synthesis of branched oligophenylenes was carried out
azine. The bromination of 10-n-octylphenothiazine with
N-bromosuccinimide (NBS) was carried out during the
second step.
by the Suzuki reaction via a polycondensation of А + В +
2 2
+ В type. The difference between obtained oligomers O-1
3
and O-2 is in the branching center, which is the 1,3,5-tris-
(phen-1,4-ylene)benzene moiety in the first case (Scheme 4)
and the 1,3,5-tris(9,9-di-n-octylfluorene-2,7-ylene)benz-
ene moiety in the second one (Scheme 5).
The branching monomer, 1,3,5-tris(4-bromophenyl)
benzene,2 was synthesized via the reaction of trimeriza-
tion cyclocondensation of 4-bromoacetophenone in the
presence of orthoformate ester25 according to Scheme 2.
4
Oligomer O-3 did not contain any phenothiazine
moieties and was synthesized for a comparison (Scheme 6).
The ratio between the tri- and di-halide compounds,
which was used in these reactions, was 1 : 3.5. This ratio
was selected since an increased proportion of the trifunc-
tional monomer in the reaction leads to a partial jellification.
Scheme 2
Usually, the molecular weights (M ) of such branched
W
oligomers are up to 8000 Da. Their values were determined
2
9
by the sedimentation method, since the data obtained
by the GPC method according to the polystyrene standard
were not reliable.
1H NMR spectra of all the three oligomers are similar.
The precise assignment of signals was not performed due
to their complicated character. We followed the published
3
0
data for assigning the signals. In the aromatic region of
1
The second branching monomer, 1,3,5-tris(7-bromo-
H NMR spectra of samples O-1 (Fig. 1) and O-3 (Fig. 2),
2
6—28
9
,9-di-n-octylfluoren-2-yl)benzene,
according to Scheme 3.
was obtained
the signals characteristic of protons of the fluorene and
phenylene moieties can be identified in the range of
Scheme 3
R = n-C H
8
17

Branched oligophenylenes with octylphenotiazine
Russ. Chem. Bull., Int. Ed., Vol. 67, No. 8, August, 2018
1435
7.883
7.698
7.494
7.506
7.676
7
.575
.565
7
7.955
7
.036
7.041
6.870
7.384
7
.039
6.964
.971
6
8
.020
8
.320
8
.5
8.0
7.5
7.0

1
Fig. 1. H NMR spectrum of the aromatic part of sample O-1.
Scheme 4

1436
Russ. Chem. Bull., Int. Ed., Vol. 67, No. 8, August, 2018
Kovalev et al.
Scheme 5
7
.4—8.4 ppm. At the same time, the spectrum of sample
O-1 contained signals related to the protons of phenothi-
1
azine moieties in the region of 6.8—7.1 ppm. The H NMR
spectrum of sample O-2 is similar to that of O-1. The
comparison of integral intensities of the proton signals in
the aromatic and aliphatic regions of oligomers revealed
that they are at the ratio of approximately 1 : 5.5 (O-1),
: 8.1 (O-2), and 1 : 2.2 (O-3), which confirmed a sig-
nificantly smaller content of octyl groups in oligomer O-3
due to the absence of substituted phenothiazine moieties
and also the largest number of such groups in oligomer
O-2 due to the use of branching monomer with the sub-
stituted fluorene groups.
1
8
1
.4 8.2 8.0 7.8 7.6 7.4 7.2 7.0

Fig. 2. H NMR spectrum of the aromatic part of sample O-3.

Branched oligophenylenes with octylphenotiazine
Russ. Chem. Bull., Int. Ed., Vol. 67, No. 8, August, 2018
1437
Scheme 6
The absorption spectra of solutions of the investigated
oligomers are shown in Fig. 3. The spectrum of sample
O-3 appears as a broad structureless band with a major
maximum at 345 nm (see Fig. 3, curve 3). In the spectrum
of sample O-1, the same band is marginally broadened
(curve 1), while its major maximum is located at a wave-
length of 337 nm. The spectrum of sample O-2 is an even
broader band with the major maximum at 328 nm (see
Fig. 3, curve 2). The shape of this spectrum allowed us to
suggest the presence of several chromophore fragments.
In addition, the long-wavelength edges of absorption bands
of samples O-1 and O-2 are approximately coincided and
located in the region of 455—460 nm. It may be assumed
that the phenothiazine moiety in the structure of these
oligomers is responsible for the observed decrease of ab-
sorption bands.
D/Dmax
1.2
0
0
.8
.4
The fluorescence spectra of solutions of the investigated
co-oligomers are significantly different from each other
(
Fig. 4). For instance, the fluorescence spectrum of
1
3
2
sample O-3 containing the chromophore moieties consist-
ing of p-substituted benzene rings and fluorene is typical
of phenylene oligomers and appears as a wide band with
the major maximum at 403 nm (see Fig. 4, curve 3). The
spectra of samples O-1 and O-2 contain the two fluores-
cence bands with the major maxima at 393 and 493 nm
(see Fig. 4, curves 1 and 2, respectively), while the long-
wave band is much more intense than the short-wave one.
2
50
300
350
400
450
/nm
Fig. 3. Absorption spectra of the solutions of samples O-1 (1),
–
5
–1
O-2 (2), and O-3 (3) in CHCl (concentration of ~10 mol L ).
3

1438
Russ. Chem. Bull., Int. Ed., Vol. 67, No. 8, August, 2018
Kovalev et al.
I (arb. units)
.2
benzene mixture of 1 : 1). The mass spectrum of compound 1
contains a molecular ion of 3,7-dibromo-10-n-octylphenothi-
1
+
1
azine ([M ] 468). The H NMR spectrum of synthesized prod-
uct was completely corresponded to that of 3,7-dibromo-10-n-
1
octylphenothiazine. H NMR (300 MHz), : 7.34 (m, 4 Н); 6.95
(
d, 2 Н); 3.81 (t, 2 Н); 1.62 (m, 2 Н); 1.31 (m, 2 Н); 1.19 (m, 8 Н);
0
0
.8
0
.81 (t, 3 Н).
,3,5-tris(4-Bromophenyl)benzene.24 4-Bromoacetophenone
7.962 g, 40 mmol) and orthoformate ester (8 mL, 48 mmol) were
1
(
3
2
1
dissolved in benzene (24 mL) in a flask. Gaseous hydrogen chlor-
ide was bubbled through the solution at room temperature and
under stirring for 3 h. The solution became brownish-red colored
and the precipitate formation began during the first hour. The
resulting precipitate was filtered off, washed with acetone and
methanol, and dried. The yield of product recrystallized from
.4
3
50
400
450
500
550
600
/nm
1
chloroform was 43.6%. The H NMR spectrum of synthesized
Fig. 4. Fluorescence spectra of the solutions of samples O-1 (1),
product (see Fig. 1) was completely corresponded to that of
2
4 1
O-2 (2), and O-3 (3) in CHCl , recorded at the excitation wave-
1,3,5-tris(4-bromophenyl)benzene.
H NMR (500 MHz), :
3
length corresponded to the maximum of absorption band (con-
7.68 (s, 3 H); 7.60 (d, 6 H, J = 8.5 Hz); 7.53 (d, 6 H, J = 8.5 Hz).
–
5
–1
centration of ~10 mol L ).
Bis(1,3-propanediol) ester of 9,9-dioctylfluorendiboronic acid
(
Aldrich, 97%) was used without purification.
Synthesis of co-oligomers (general procedure). Sample O-1.
It appears due, most likely, to the inclusion of pheno-
thiazine moiety into the chromophore fragments of oligo-
mers. The fluorescence spectra of all the three compounds
do not depend on the excitation wavelength. Moreover,
the long-wavelength fluorescence bands of samples O-1
and O-2 are almost identical in their shape and position.
This allows us to assume that the optical centers respon-
sible for the long-wavelength fluorescence of these com-
pounds possess a similar structure.
Therefore, the solutions of synthesized oligomers pos-
sess the fluorescence in the region of 350—650 nm, while
the spectra of oligomers containing phenothiazine are
shifted to the long-wave region. The obtained oligomers
form thin transparent films that also exhibit the fluores-
cence, which allows them to be applied as the active layers
in electroluminescent devices.
1,3,5-tris(4-Bromophenyl)benzene (0.123 g, 0.226 mmol), bis-
(
(
(
1,3-propanediol) ester of 9,9-dioctylfluorendiboronic acid
0.631 g, 1.13 mmol), and 3,7-dibromo-10-n-octylphenothiazine
0.371 g, 0.791 mmol) were dissolved in toluene (5 mL) in the
Schlenk tube equipped with a magnetic stirrer. Aqueous K CO3
2
solution (2 M, 2 mL) was added to the reaction mixture, and the
gaseous products were repeatedly evacuated from the reaction
mixture under stirring in vacuo. Tetrakis(triphenylphosphino)
palladium (0.156 g, 0.135 mmol) was then added to the reaction,
and the reaction system was again evacuated and filled with argon.
The mixture was heated to 70 C and held at this temperature
under stirring for 3 days. After cooling the reaction solution, the
product was precipitated with an organic mixture (methanol : wa-
ter, 9 : 1). The precipitate was filtered off, washed with methanol,
and extracted with chloroform in the Soxhlet apparatus for 5 h;
the product solution in chloroform was evaporated, and the
product was precipitated with ethanol. The precipitate was filtered
off, washed with ethanol, and dried in vacuo. The product was
isolated as a yellow powder in the yield of 49.3%.
Samples O-2 and O-3 were synthesized according to the
similar procedure.
Experimental
1
,3,5-tris(7-Bromo-9,9-di-n-octylfluoren-2-yl)benzene.26—28
1
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in revised form May 7, 2018;
accepted May 28, 2018
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