Synthesis, structural and spectral properties of diarylamino-functionalized pyrene derivatives via Buchwald-Hartwig amination reaction

Article abstract of DOI:10.1016/j.molstruc.2012.09.028

A new series of diarylamino-functionalized pyrene derivatives, namely, 1-(N,N-diarylamino)-substituted pyrenes (7), isomer of 1,6-bis- and 1,8-bis(N,N-diarylamino)-substituted pyrenes (8/9) and 1,3,6,8-tetrakis(N,N- diarylamino)-substituted pyrenes (10) have been synthesized. The structures of these synthesized compounds were determined on the basis of spectral data and elemental analysis. All compounds 7-10 have bright fluorescent emissions from sky-blue to green in solution condition (λ_max = 464-500 nm in CH₂Cl₂) and high emission efficiency (Φ_f = 0.84-0.96 in dichloromethane). All compounds have high thermal stability and good solubility in common organic solvents. The electronic properties of these compounds were determined by spectroscopic methods such as UV-vis absorption spectroscopy and fluorescence emission spectroscopy. Clear evidences were obtained that the longest wavelength bands of these compounds are bathochromically red-shifted as the number of the diarylamino-substituent increased.

Full text of DOI:10.1016/j.molstruc.2012.09.028

Journal of Molecular Structure 1035 (2013) 19–26
Contents lists available at SciVerse ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Synthesis, structural and spectral properties of diarylamino-functionalized
pyrene derivatives via Buchwald–Hartwig amination reaction
Jian-Yong Hu a, Xing Feng a, Nobuyuki Seto a, Jung-Hee Do a, Xi Zeng b, Zhu Tao b, Takehiko Yamato a,
⇑
a Department of Applied Chemistry, Faculty of Science and Engineering, Saga University, Honjo-machi 1, Saga-shi, Saga 840-8502, Japan
b Key Laboratory of Macrocyclic and Supramolecular Chemistry of Guizhou Province, Guizhou University, Guiyang, Guizhou 550025, People’s Republic of China
h i g h l i g h t s
"
"
"
Diarylamino-pyrenes were synthesized by a modified Buchwald–Hartwig amination reaction.
All compounds emit very bright fluorescent emissions in solution (Uf = 0.84–0.96 in dichloromethane).
Diarylamino groups suppress p-stacking in the solid state.
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 21 July 2012
Received in revised form 7 September 2012
Accepted 7 September 2012
Available online 19 September 2012
A new series of diarylamino-functionalized pyrene derivatives, namely, 1-(N,N-diarylamino)-substituted
pyrenes (7), isomer of 1,6-bis- and 1,8-bis(N,N-diarylamino)-substituted pyrenes (8/9) and 1,3,6,8-tetra-
kis(N,N-diarylamino)-substituted pyrenes (10) have been synthesized. The structures of these synthe-
sized compounds were determined on the basis of spectral data and elemental analysis. All
compounds 7–10 have bright fluorescent emissions from sky-blue to green in solution condition
(kmax = 464–500 nm in CH2Cl2) and high emission efficiency (Uf = 0.84–0.96 in dichloromethane). All
compounds have high thermal stability and good solubility in common organic solvents. The electronic
properties of these compounds were determined by spectroscopic methods such as UV–vis absorption
spectroscopy and fluorescence emission spectroscopy. Clear evidences were obtained that the longest
wavelength bands of these compounds are bathochromically red-shifted as the number of the diarylami-
no-substituent increased.
Keywords:
Pyrenes
Hole-transporting materials
Buchwald–Hartwig amination reaction
Diarylamino-functionalized pyrenes
Fluorescence emission properties
Ó 2012 Elsevier B.V. All rights reserved.
1. Introduction
bi-furyl derivatives [12], and dithioenosilole [13] and dicarbazolyl
[14] derivatives containing peripheral triarylamines. Moreover, for
Since Tang and co-workers firstly demonstrated that the use of
hole-transporting layers (HTLs) for hole injection from the anodes
into the light-emitting layer could provides the significant
improvement of the OLED device performance [1], much attention
have been devoted to the development of new hole-transporting
materials [2] in recent years. Recently, small molecule weight tria-
rylamine derivatives have attracted much interest as hole-trans-
porting materials (HTMs) for use in multilayer OLEDs [3–5] due
to their high mobility and are easily oxidized to form stable radical
cations that act as hole-transporting species. Furthermore, they are
easily purified by vapor deposition techniques or column chroma-
tography and uniform thin film can be prepared by simple coating
techniques. Examples of triarylamine-based HTM are 4,40-bis-
(m-tolylphenylamino) of biphenyl (TPD) [6–8], bistriphenylamine
end-capped oligothiophenes [9], spiro-silabifluorene [10,11] and
practical OLED devices, a simple structure hole-transporting mate-
rial (HTM) with high mobility of hole, stable amorphous state, easy
form good thin film by spin-coating techniques, and preferable a
simple preparation is necessary. Therefore, there are continually
research interest in the design and synthesis of new HTMs materi-
als with excellent properties.
As a large conjugated aromatic ring, pyrene not only has the
advantages of high PL efficiency [15], high carrier mobility, but also
has the much improved hole-injection ability than oligofluorenes
or polyfluorene [16]. More recently, some pyrene derivatives have
been successfully used in OLEDs to improve hole-transporting abil-
ity arising from their electron-rich property [17,18].
Thus there is substantial interest in investigating new pyrene
derivatives with excellent properties as promising candidates for
high-performance OLEDs applications. Recently, pyrene-based
materials for organic electronics, which include the Pd-catalyzed
Suzuki and Sonogashira cross-coupling reactions bromopyrenes
were widely developed [19]. In this paper, we wish to report here
⇑
Corresponding author. Tel.: +81 952 28 8679; fax: +81 952 28 8548.
E-mail address: yamatot@cc.saga-u.ac.jp (T. Yamato).
0022-2860/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.molstruc.2012.09.028

20
J.-Y. Hu et al. / Journal of Molecular Structure 1035 (2013) 19–26
the synthesis of three types of pyrene derivatives that combined
the high hole mobility function of diarylamine as substituents with
the high efficiency and hole-injection ability of pyrene as the con-
jugation core, by using a modified Buchwald–Hartwig amination
reaction. Moreover, photophysical properties of these compounds
are fully examined in solution through spectroscopy techniques.
mon organic solvents. The 1H NMR spectrum was not obtained in
CDCl3 due to the limited solubility of this compound.
2.1.4. Synthesis of 1-(N,N-diphenylamino)pyrene (7a)
The corresponding 1-bromopyrene (2) (300 mg, 1.07 mmol),
diphenylamine (6a) (272 mg, 1.60 mmol, 1.5 mol of amine per hal-
ogen atom of bromopyrene), Pd(OAc)2 (1 mol% of Pd per halogen
atom of bromopyrene), (t-Bu)3P (3 mol% of P per halogen atom of
bromopyrene), Cs2CO3 (1.5 mol of Cs per halogen atom of bromop-
yrene), and o-xylene (10 mL) were mixed together and heated at
160 °C for 12 h. The reaction was quenched with water (30 mL)
and the organic layer taken into 100 mL of CH2Cl2, washed with
brine solution, and dried over MgSO4. Evaporated of the solvent
under vacuum resulted in a solid residue. The residue was ad-
sorbed in silica gel (Wako gel, C-300) and purified by column chro-
matography using hexane as eluent and recrystallization from
ethyl acetate to afford the corresponding desired compound 7a
as pale-yellow powder (258 mg, 65%); m.p. 202–204 °C; dH (CDCl3)
6.92–7.23 (10H, m, Ar-H) and 7.90–8.37 (9H, m, Py-H); dH (CDCl3)
122.12, 123.55, 124.89, 124.95, 125.03, 125.93, 126.12, 126.35,
126.85, 127.23, 127.38, 127.63, 127.97, 129.21, 129.73, 131.05,
131.12, 131.30, 141.48 and 146.60; m/z 369 (M+) (Found: C,
91.05; H, 5.22, N, 3.78%. C28H19N (369.46) requires C, 91.03; H,
5.18; N, 3.79%).
2. Experimental
1H/13C NMR spectra were recorded at 300 MHz and 75 MHz on
a Nippon Denshi JEOL FT-300 NMR spectrometer in deuteriochlo-
roform with Me4Si as an internal reference. The IR spectra were ob-
tained as KBr pellets on a Nippon Denshi JIR-AQ2OM spectrometer.
Mass spectra were obtained on a Nippon Denshi JMS-HX110A
Ultrahigh Performance Mass Spectrometer at 75 eV using
a
direct-inlet system. Elemental analyses were performed by Yanaco
MT-5. UV–vis spectra were recorded on a Perkin Elmer Lambda 19
UV/VIS/NIR spectrometer. Emission spectra were performed in a
semimicro fluorescence cell (HellmaÒ, 104F-QS, 10 ꢀ 4 mm,
1400 lL) with a Varian Cary Eclipse spectrophotometer. Gas–liquid
chromatograph (GLC) analyses were performed by Shimadzu gas
chromatograph, GC-14A; silicone OV-1, 2 m; programmed temper-
ature rise, 12 °C minꢁ1; carrier gas nitrogen, 25 mL minꢁ1
.
2.1. Synthesis
2.1.5. Synthesis of 1-[N,N-di(4-methylphenyl)amino]pyrene (7b)
Similarly, 1-[N,N-di(4-methylphenyl)amino]pyrene (7b) was
obtained in 75% yield as pale-yellow prisms (hexane-methanol
1:1); m.p. 176–178 °C; dH (CDCl3) 2.28 (6H, s, Me), 6.94 (4H, d,
J = 8.7 Hz, Ar-H), 7.00 (4H, d, J = 8.7 Hz, Ar-H) and 7.78–8.16 (9H,
m, Py-H); dH (CDCl3) 20.66, 122.09, 123.52, 124.86, 124.91,
124.99, 125.90, 126.08, 126.32, 126.81, 127.20, 127.34, 127.59,
127.94, 129.18, 129.70, 131.02, 131.08, 131.27, 141.45 and
146.58; m/z 397 (M+) (Found: C, 90.56; H, 5.84; N, 3.50%.
2.1.1. Synthesis of 1-bromopyrene (2)
A solution of NBS (187 mg, 1.05 mmol) in dry DMF (5 mL) was
added to a solution of pyrene (252 mg, 1.0 mmol) in dry DMF
(10 mL) and stirred at room temperature 24 h [20]. After reaction,
the mixture was poured into water (50 mL) and extracted with
dichloromethane (100 mL). The extract was washed well with
water, dried (MgSO4), and evaporated under reduced pressure to
yield crude product 2 as a pale-yellow solid (332 mg, 85%). Recrys-
tallization from hexane afforded 1-bromopyrene (2) as pale-yellow
powder; m.p. 103–104 °C (m.p. 102–104 °C) [21].
C30H23N (397.51) requires C, 90.64; H, 5.83; N, 3.52%).
2.1.6. Synthesis of isomer of 1,6- and 1,8-bis-(N,N-
diphenylamino)pyrene (8a/9a)
2.1.2. Synthesis of 1,6-di- and 1,8-dibromopyrene (3) and (4)
The corresponding di-bromopyrene (3/4) (300 mg, 0.66 mmol),
diphenylamine (6a) (335 mg, 1.98 mmol, 2.5 mol of amine per hal-
ogen atom of bromopyrene), Pd(OAc)2 (2 mol% of Pd per halogen
atom of bromopyrene), (t-Bu)3P (6 mol% of P per halogen atom of
bromopyrene), Cs2CO3 (2.5 mol of Cs per halogen atom of bromop-
yrene), and o-xylene (10 mL) were mixed together and heated at
120 °C for 48 h. The reaction was quenched with water (100 mL)
and the organic layer taken into 100 mL of CH2Cl2, washed with
brine solution, and dried over MgSO4. Evaporated of the solvent
under vacuum resulted in a solid residue. The residue was ad-
sorbed in silica gel (Wako gel, C-300) and purified by column chro-
matography using hexane as eluent and recrystallization from
ethyl acetate to afford the corresponding desired compounds 8a/
9a as pale-yellow powder (205 mg, 68%); m.p. 288–290 °C; dH
(CDCl3) 6.89–7.24 (20H, m, Ar-H) and 7.79–8.16 (8H, m, Py-H);
m/z 537 (M+) (Found: C, 89.50; H, 5.24; N, 5.23%. C40H28N2
(536.66) requires C, 89.52; H, 5.26; N, 5.22%).
A
solution of 1,3-dibromo-5,5-dimethylhydantoin (DBMH)
(308 mg, 1.1 mmol) in dry CH2Cl2 (10 mL) was added to a solution
of pyrene (252 mg, 1.00 mmol) in dry CH2Cl2 (40 mL) and stirred at
room temperature for 1 h [22]. The mixture was poured into water
(50 mL) and extracted with dichloromethane (200 mL). The extract
was washed well with water, dried (MgSO4), and evaporated under
reduced pressure to yield crude products. The crude products were
successfully washed with CH2Cl2 (15 mL) to give a mixture of
1,6-di- and 1,8-dibromopyrene 3 and 4 as an orange-yellow
solid (398 mg, 97%); m.p.123–124 °C. Separation of 1,6-di- and
1,8-dibromopyrene 3 and 4 was reported in the literature (m.p.
230–231 °C for 3 and m.p. 210–211 °C for 4) [23]. However, several
attempted separations of the mixture of 3 and 4 into each pure
failed. The mixture of isomers of 1,6-di- and 1,8-dibromopyrene
(3 and 4) was directly used to carry out next Buchwald–Hartwig
amination reaction.
2.1.3. Synthesis of 1,3,6,8-tetrabromopyrene (5)
Bromine (8.75 g, 0.055 mol) was added dropwise, with vigorous
stirring to a solution of pyrene (2.5 g, 12.3 mmol) in nitrobenzene
(50 mL) at 80 °C [24]. Then the mixture was heated to 120 °C and
kept for 12 h. After cooled to room temperature, the mixture was
filtered, washed with ethanol (100 mL), and dried under vacuum
to afford 5 (6.04 g, 96%) as a pale-green solid; m.p. >300 °C (m.p.
>300 °C) [21]. (Found C, 36.85; H, 1.23. C16H6Br4 (517.84) requires
C, 37.11; H, 1.17%). This compound was quite insoluble in all com-
2.1.7. Synthesis of isomer of 1,6- and 1,8-bis-[N,N-di-
(4-methylphenyl)amino]pyrene (8b/9b)
Similarly, 1,6- and 1,8-bis-[N,N-di(4-methylphenyl)amino] pyr-
ene (8b/9b) was obtained in 73% yield as pale-yellow prisms
(methanol); m.p. 196–198 °C; dH (CDCl3) 2.26, 2.28 (12H, s, Me),
6.88–7.02 (16H, m, Ar-H) and 7.74–8.12 (8H, m, Py-H); m/z 593
(M+) (Found: C, 89.16; H, 6.10; N, 4.75%. C44H36N2 (592.77) re-
quires C, 89.15; H, 6.12; N, 4.73%).

J.-Y. Hu et al. / Journal of Molecular Structure 1035 (2013) 19–26
21
2.1.8. Synthesis of 1,3,6,8-tetrakis-(N,N-diphenylamino)pyrene (10a)
The corresponding tetrabromopyrene (5) (300 mg, 0.58 mmol),
secondary amines (6a) (588 mg, 3.48 mmol, 6.0 mol of amine per
halogen atom of tetrabromopyrene), Pd(OAc)2 (4 mol% of Pd per
halogen atom of bromopyrene), (t-Bu)3P (12 mol% of P per halogen
atom of tetrabromopyrene), Cs2CO3 (10 mol of Cs per halogen atom
of tetrabromopyrene), and o-xylene (10 mL) were mixed together
and heated at 160 °C for 48 h. The reaction was quenched with
water (100 mL) and the organic layer taken into 100 mL of CH2Cl2,
washed with brine solution, and dried over MgSO4. Evaporated of
the solvent under vacuum resulted in a solid residue. The residue
was adsorbed in silica gel (Wako gel, C-300) and purified by col-
umn chromatography using hexane/CHCl3 (6:1) as eluent and
recrystallization from ethyl acetate to afford the corresponding de-
sired compound 10a as pale-yellow powder (378 mg, 72%); m.p.
>300 °C; dH (CDCl3) 6.89–7.17 (40H, m, Ar-H), 7.66 (2H, s, Py-Ha)
and 7.97 (4H, s, Py-Hb); dC (CDCl3) 117.80, 121.82, 123.33,
127.37, 129.09, 129.31, 130.53, 141.91 and 148.12; m/z 871 (M+)
(Found: C, 88.23; H, 5.34; N, 6.45%. C64H46N4 (871.08) requires C,
88.25; H, 5.32; N, 6.43%).
(3 and 4) was directly used to carry out next Buchwald–
Hartwig amination reaction using the –C–N– as linked bridge.
The Buchwald–Hartwig amination reactions were carried out be-
tween the 1-bromopyrene 2, 1,3,6,8-tetrabromopyrene 5 and the
diphenylamines 6 under the modified reaction conditions [25,26]
to afford the targets 1-(N,N-diarylamino)- and 1,3,6,8-tetrakis-
(N,N-diarylamino)-subsituted pyrenes 7(a/b) and 10(a/b) in good
yields, respectively. Similarly, the mixture of 3 and 4 was reacted
with the diphenylamines 6a and 6b afforded 8a/9a and 8b/9b in
68% and 73% yields, respectively (Scheme 1). Both the 1-substituted
pyrenes (7a/b) and the tetra-subsituted pyrenes (10a/b) were suc-
cessfully purified by column chromatography and recrystallization.
Although several attempted isolations of the mixture of 1,6- and
1,8-bis-substituted pyrenes (8a/8b and 9a/9b) in each pure form
failed, the two mixtures of compounds, 8a/9a and 8b/9b were
directly used to determine their photophysical properties.
The structures of these new diarylamino-functionalized pyrene
derivatives 7–10 were fully characterized by 1H/13C NMR, mass
spectroscopy as well as elemental analysis. In particular, due to their
C2h point-group symmetric structures, their 1H NMR spectrum of
these tetra-substituted pyrene derivatives 10a and 10b are very sim-
ple, for example, the compound 1,3,6,8-tetrakis[N,N-di-(4-methyl-
phenyl)]pyrene 10b display two singlet at d = 7.93 ppm and
7.57 ppm for the pyrene ring protons at 4-, 5-, 9-, and 10-positions
and 2-, 7-positions, respectively, a pair of doublets in a 1:1 ratio in
the region at d = 6.93 and d = 6.85 ppm for the aromatic protons, a
singlet at d = 2.35 ppm for the eight methyl groups protons. Simulta-
neously, the structures of 7–10 were further established on the basis
of the base peak molecular ion at m/z [M+] 369 for 7a, 397 for 7b, 537
for 8a/9a, 593 for 8b/9b, 871 for 10a, and 983 for 10b in their mass
spectrum, respectively. All resultswere wellconsistentwith thepro-
posed structures. On the other hand, these three types of diarylami-
no-functionalized pyrenes 7–10 are very stable solids with colors of
from orange to red that can be stored in air for prolonged period of
times at room temperature. All compounds have good solubility in
all the common organic solvents including hexane with melting
points from 176 °C to over 300 °C, increasing as the number of the
diarylamino-substituents.
2.1.9. Synthesis of 1,3,6,8-tetrakis-[N,N-di-
(4-methylphenyl)amino]pyrene (10b)
Similarly,
1,3,6,8-tetrakis-[N,N-di(4-methylphenyl)amino]-
pyrene (10b) was obtained in 75% yield as pale-yellow prisms
(ethyl acetate); m.p. > 300 °C; dH (CDCl3) 2.35 (24H, s, Me), 6.85
(16H, d, J = 8.7 Hz, Ar-H), 6.93 (16H, d, J = 8.7 Hz, Ar-H), 7.57 (2H,
s, Py-Ha) and 7.93 (4H, s, Py-Hb); dC (CDCl3) 20.61, 121.71,
123.14, 127.06, 128.27, 129.59, 130.13, 130.87, 142.05 and
146.03; m/z 983 (M+) (Found: C, 87.93; H, 6.38; N, 5.69%.
C72H62N4 (983.29) requires C, 87.95; H, 6.36; N, 5.70%).
2.2. Single-crystal X-ray diffraction measurements
Crystallographic data for 10a: C64H46N4, M = 871, triclinic, P21/c,
a = 9.351(7), b = 11.990(9), c = 22.790(19) Å,
a = 85.770(13),
b = 79.677(13),
c
= 68.499(13), V = 2339(3) Å3, Z = 2, Dc = 1.237 g cmꢁ3
,
T = 293(2) K, pale-yellow prisms; 15761 reflections measured on a
Rigaku Saturn CCD diffratometer, of which 7903 were indepen-
dent, data corrected for absorption on the basis of symmetry
equivalent and repeated data (min and max transmission factors:
0.896 0.997) and Lp effects, Rint = 0.1794, structure solved by direct
methods (Sir2002), F2 refinement, R1 = 0.0819 for 3757 data with
The molecular structure of compound 10a was further con-
firmed by single-crystal X-ray analysis. The crystals were grown
by slow evaporation of a CHCl3 concentrated solution. This com-
pound was obtained as orange needles and provided excellent
quality data. The crystallographic data for this compound 10a are
summarized in Table 1.
Structure diagrams of 10a are shown in Fig. 1i and ii. The mol-
ecule lies on a onefold axis; thus all is crystallographically unique.
The four diphenylamino groups are completely twisted against the
F2 > 2 (F2), wR2 = 0.2518 for all data, 614 parameters, Crystallo-
r
graphic data (excluding structure factors) for the structures in this
paper have been deposited with the Cambridge Crystallographic
Data Centre as supplementary publication numbers CCDC
892550. Copies of the data can be obtained, free of charge, on
application to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK
[fax: +44 1223 336033 or e-mail: deposit@ccdc.cam.ac.uk].
central pyrene ring with certain angles. Generally, the efficient p-
stacking in emitting molecules could lead to extensive excimer for-
mation in the solid state or thin film with low quantum yields of
fluorescence. The crystal packing diagrams of 10a are also shown
in Fig. 1iii. No crystal packings were observed in this crystal due
to the big sterically hindrance arising from the bulky diphenyl-
amino groups attached in the pyrene ring at 1-, 3-, 6-, and 8-posi-
tions. Thus, these newly prepared diarylamino-functionalized
3. Results and discussion
1-Bromopyrene 2 was prepared by brominating of pyrene 1 with
N-bromosuccinimide (NBS) in DMF at room temperature for 24 h
according to the previous reported procedure [20]. Bromination of
pyrene 1 with 1.1 equivalents of 1,3-dibromo-5,5-dimethylhydan-
toin (DBMH) [22] in CH2Cl2 at room temperature for 1 h afforded a
mixture of 1,6-di- and 1,8-dibromopyrene 3 and 4 in yield of 97%.
1,3,6,8-Tetrabromopyrene 5 was readily obtained by the exhaustive
bromination of pyrene 1 with 4.5 equivalents of bromine in nitro-
benzene at 120 °C for 12 h as following the previous reported proce-
dures (Scheme 1) [24]. Although attempted separation of the
mixture of 1,6- and 1,8-dibromopyrene (3 and 4) into each pure
failed, the mixture of isomers of 1,6-di- and 1,8-dibromopyrene
pyrenes with less
gests that they might be advantageous as promising emitters in
p p stacking intermolecular interactions sug-
ꢁ
optoelectronic device applications.
The UV/vis absorption and fluorescence spectra of these three
types of diarylamino-substituted pyrenes 7–10 were measured in
dichloromethane (CH2Cl2) and the key photophysical data are
listed in Table 2.
The spectroscopic properties of these diarylamino-functional-
ized pyrene derivatives 7–10 were measured in dichloromethane
(CH2Cl2) solution at 25 °C and are shown in Figs. 2 and 3,
respectively.

22
J.-Y. Hu et al. / Journal of Molecular Structure 1035 (2013) 19–26
Scheme 1.
Table 1
rakis-(N,N-diphenylamino)-substituted pyrenes 10a and 10b, the
pꢂ maxima band were observed at 461 and 472 nm, respec-
Summary of the crystal data of compound 10a.
p–
tively, which are gradually red-shifted ca. 120 nm and 130 nm
compared to that of unsubstituted pyrene 1, respectively. Further-
more, there is a slight red-shift in the absorption spectra of 7b rel-
ative to that of 7a, which can be ascribed to the electron-donating
ability of methyl groups. Similar results can also be observed in the
absorption spectra of 8/9 and 10. Thus, these results strongly indi-
cate that not only the number of substituents but also the differ-
ence of substituents characteristics can significantly affect the
spectroscopic properties of these diarylamino-functionalized
pyrenes.
The fluorescence-emission spectra of 7–10 are shown in Fig. 3.
Dilute solutions of 7–10 in dichloromethane showed sky-blue to
green emission as the number of substituent increased. It is inter-
esting that the compounds that have methyl groups (7b, 8b/9b and
10b) showed significantly red-shifted fluorescence relative to
those that have no methyl groups (7a, 8a/9a and 10a). On the other
hand, the emission maxima of 7a, 8a/9a, and 10a, consecutively
shifted to longer wavelengths at 464, 481 and 494 nm, in a manner
similar to their absorption maxima and the fluorescence spectra of
7b, 8b/9b and 10b, are also varied at 474, 494 and 500 nm, respec-
tively, also in agreement with the electronic absorption spectra.
These phenomena can also be observed in some carbazole-based
dendrimers [27] and several phenylethynyl-substituted pyrene
derivatives [28,29]. The fluorescence spectrum of 10b was the
most red-shifted among all the compounds examined (Table 2).
The fluorescence quantum yields (Uf) of 7–10 recorded in
dichloromethane are also presented in Table 2. The Uf values of
7–10 were found in the range of 0.84–0.96 relative to that of
9,10-diphenylanthracene (0.90 in cyclohexane) [29].
Parameter
10a
Empirical formula
C
64H46N4
Formula weight (g molꢁ1
Temperature (K)
Wavelength (Å)
Crystal system
)
871.05
293(2)
0.71073
triclinic
P21/c
pale yellow, 0.25 ꢀ 0.23 ꢀ 0.18
9.351(7)
11.990(9)
22.790(19)
85.770(13)
79.677(13)
68.499(13)
2339(3)
2
1.237
0.072
916
0.91–25.01
15761
7903
2019
0.1794
0/614
Space group
Crystal color and size (mm3)
a (Å)
b (Å)
c (Å)
a
(°)
b (°)
c
(°)
Volume (Å3)
Z
Density, calcd (g mꢁ3
)
Absorption coefficient (mmꢁ1
F(000)
)
h range for data collection (°)
Reflections collected
Independent reflections
Observed data [F2 > 2
r
(F2)]
Rint
Restraints/parameters
Goodness-of-fit on F2
0.788
0.0819
0.2518
R1 [F2 > 2
r
(F2)]
wR2 (all data)
As shown in Fig. 2, the absorption spectra of 7–10 showed a p–
pꢂ band at ꢃ379–472 nm. Consequently, for the 1-(N,N-diarylami-
no)-substituted pyrenes, the absorption maxima of 7a (379 nm)
and 7b (407 nm) are red-shifted ca. 40 nm and 70 nm compared
with that of unsubstituted pyrene 1 (336 nm), for the isomer of
1,6-bis- and 1,8-bis-(N,N-diphenylamino)-substituted pyrenes (8a/
9a) and (8b/9b), the absorption spectra maxima (422 nm for 8a/
9a and 431 nm for 8b/9b) are red-shifted ca. 80 and 90 nm relative
to that of unsubstituted pyrene 1, respectively, and the 1,3,6,8-tet-
To obtain better understanding of the electronic spectroscopic
properties of these diarylamino-functionalized pyrenes, the 1-
substituted pyrene 7b and the tetrakis-substituted pyrene 10b
were selected as the candidates, and the optical absorption and
emission spectroscopic data of 7b and 10b recorded in various sol-
vents are summarized in Table 3.

J.-Y. Hu et al. / Journal of Molecular Structure 1035 (2013) 19–26
23
(i)
(ii)
(iii)
Fig. 1. X-ray structure diagram of compound 10a (i) top view; (ii) side view; (iii) packing diagrams.
It is well known that the solvatochromitic effect is not only de-
pends on the molecular structure, but also depends on the nature
of the chromophore, and the solvents [30]. Each molecule shows
a certain solvatochromic behavior (Figs. 4 and 5). The emission
spectrum exhibits a more significant red shift in polar solvents
than in nonpolar solvents (see Table 3). For example, the emission

24
J.-Y. Hu et al. / Journal of Molecular Structure 1035 (2013) 19–26
Table 2
Photophysical data of compounds 7ꢁ10 and pyrene (1).a
Compound
Absorption kmax (nm)b
Fluo. emission kmax (nm)c
loged (Mꢁ1 cmꢁ1
)
Stokes-shift (nm)
Ufe
1
7a
7b
8a/9a
8b/9b
10a
10b
336
379
409
422
431
461
472
374
464
474
481
489
494
500
nd
38
85
65
59
58
33
28
nd
4.79
4.80
5.04
5.05
5.31
5.32
0.96
0.84
0.89
0.91
0.94
0.92
nd: No determination.
a
All spectra were recorded for ꢃ10ꢁ5 to 10ꢁ6 M concentration in dilute CH2Cl2 solution at room temperature.
At 1.0 ꢀ 10ꢁ5 M, kabs is the absorption band appearing at the longest wavelength.
At ꢃ10ꢁ6 M, kem is the fluorescence band appearing at the shortest wavelength.
Which were calculated at concentration of 1 ꢀ 10ꢁ5 M.
b
c
d
e
Fluorescence quantum yield, determined at 1.0 ꢀ 10ꢁ6 M concentration, relative that of 9,10-diphenylanthrathcene (0.90 in cyclohexane).
A
Fig. 2. UV–vis absorption spectra of compounds 7a, 7b, 8a/9a, 8b/9b, 10a and 10b.
All compounds are measured in dichloromethane at 1.0 ꢀ 10ꢁ5 M concentration at
25 °C.
B
maxima of 7a in N,N-dimethylformamide (DMF) (504 nm) is ca.
64 nm red-shifted from that in cyclohexane (440 nm) (Fig. 5A).
Similarly, the emission maxima of 10b gradually increases (ca.
20 nm) going from cyclohexane (490 nm) to DMF (510 nm)
(Fig. 5B). This solvatochromism can be attributed to the decease
in the energy of the singlet excited states as a function of an in-
crease in the polarity of the solvents.
1.0
0.8
0.6
Typically, a fluorophore has a larger dipole moment in the ex-
cited state than in the ground state. Following excitation, solvent
dipoles can reorient or relax lowing the energy of the excited state
0.4
0.2
[30]. So, these results above observed indicated that the le (dipole
moment of 7b and 10b in the excited state) should be larger than
the lg (the dipole moment of 7b and 10b in the ground state) be-
cause a positive solvatochromic effect was observed. On the other
hand, the solvatochromic effect indicates the compounds possess
intramolecular charge transfer (ICT) from the donor (diarylamine)
to the acceptor (pyrene center) units [31]. Interestingly, although
compound 10b has a more number of substituent, it shows less
solvatochromic shift compared with that of compound 7b. This
may be due to 10b bearing more symmetrical than 7b, which re-
sults in lower excited dipole of 10b getting less stabilization by
the solvent dipole [32].
Fig. 3. (A) Normalized fluorescence-emission spectra of compounds 7a, 7b, 10a and
10b; and (B) normalized fluorescence-emission spectra of compounds 8a/9a and
8b/9b. All compounds are measured in dichloromethane at ꢃ10ꢁ6 M concentration
at 25 °C, compared with that of unsubstituted pyrene (1).
are indeed zero because they are possessed centre-symmetric in
the ideal C2h symmetry, these results obtained above demonstrated
that the Qe (the quadrupole moments of 10 in the excited state)
should be larger than the Qg (the quadrupole moments of 10 in
the ground state) because the positive solvatochromic effects were
observed in both the absorption spectra and the emission spectra,
which implies that there is a change in the quadropole moment
These results further indicated that the le (the dipole moments
of 7 and 10 in the excited state) should be the little larger than the
lg (the dipole moments of 7 and 10 in the ground state) because
the positive solvatochromic effects were observed in both the
absorption spectra and the emission spectra [33,34]. Although
the dipole moments of 10 in either the ground or excited states

J.-Y. Hu et al. / Journal of Molecular Structure 1035 (2013) 19–26
25
Table 3
Optical absorption and emission spectroscopic data for compounds 7b and 10b in various solvents at 25 °C.a
Compound
Solventb
Absorption kmax (nm)c
Fluo. emission kmax (nm)d
Stokes-shift (nm)
Ufe
CCH
THF
DCM
CHCl3
DMF
412
409
408
407
406
440 (246)
474 (248)
478 (330)
484 (277)
504 (302)
28
65
70
77
98
0.53
0.62
0.84
0.69
0.56
7b
CCH
THF
DCM
CHCl3
DMF
469
472
473
474
476
490 (259)
500 (260)
502 (300)
503 (307)
510 (296)
21
28
29
29
34
0.96
0.85
0.92
0.98
0.88
10b
a
b
c
All spectra were measured for ꢃ10ꢁ5 to 10ꢁ6 M concentration in different solvents at 25 °C.
CCH: cyclohexane; THF: tetrahydrofuran; DCM: dichloromethane; CHCl3: chloroform; DMF: N,N-dimethylformamide.
ꢃ10ꢁ5 M in different solvents, kabs is the absorption band appearing at the longest wavelength.
ꢃ10ꢁ6 M in different solvents, kabs is the fluorescence band appearing at the shortest wavelength.
d
e
Fluorescence quantum yield were determined at 1.0 ꢀ 10ꢁ6 M in cyclohexane and dichloromethane solution by absolute methods.
A
A
B
B
Fig. 4. (A) Normalized UV–vis absorption spectra of 7b and (B) normalized UV–vis
absorption spectra of 10b recorded in (a) cyclohexane (CCH), (b) tetrahydrofuran
(THF), (c) dichloromethane (DCM), (d) chloroform (CHCl3), and (e) N,N-dimethyl-
formamide (DMF) at ꢃ10ꢁ5 M concentration at 25 °C.
Fig. 5. (A) Normalized emission spectra of 7b and (B) normalized emission spectra
of 10b recorded in (a) cyclohexane (CCH), (b) tetrahydrofuran (THF), (c) dichloro-
methane (DCM), (d) chloroform (CHCl3), and (e) N,N-dimethylformamide (DMF) at
ꢃ10ꢁ6 M concentration at 25 °C.

26
J.-Y. Hu et al. / Journal of Molecular Structure 1035 (2013) 19–26
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A series of diarylamino-functionalized pyrenes 7–10 have been
synthesized in high yields by a modified Buchwald–Hartwig ami-
nation reaction. Photophysical properties studies of 7–10 indicated
that there are significant effects on the UV–vis absorption spectra
and the emission spectra as the number of diarylamino-substitu-
ent increased. All compounds 7–10 emit very bright fluorescent
emissions, from sky-blue to green in solution (Uf = 0.84–0.96 in
dichloromethane), and have good solubility in common organic
solvents and high stability. Slight solvatochromic effects can be ob-
served for the mono-diarylamino-substituted pyrenes 7 and the
tetra-diarylamino-substituted pyrenes 10 in solutions, which im-
ply that these current compounds 7 and 10 are more solvated in
the excited state than in the ground state. The herein-presented
molecules are exciting new materials that combine excellent opti-
cal features and an improved thermal stability. Thus, their poten-
tial applications in OLEDs can be suggested and further
explorations into this area are currently under study in our
laboratory.
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Acknowledgments
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This work was performed under the Cooperative Research Pro-
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(Institute for Materials Chemistry and Engineering, Kyushu
University)’’.
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