Synthesis and properties of a new AIE macrocyclic emitter with triarylamine backbone

Article abstract of DOI:10.1016/j.tetlet.2017.08.004

A new macrocyclic AIE emitter composed of triarylamine backbone was successfully synthesized through convenient homocoupling procedure and easily purified by silica gel column chromatography, and recrystallization. The optical and electrochemical properties of the compound have been investigated. Intriguingly, the compound shows dual emission both 423 nm and 505 nm. This result implied that the violet emission was originated from an isolated component of the emitter, whereas the yellowish-green emission simultaneously exhibited AIE nature. The compound exhibits enough thermal stability and high glass transition temperature to be applied for organic devices.

Full text of DOI:10.1016/j.tetlet.2017.08.004

Accepted Manuscript
Synthesis and properties of a new AIE macrocyclic emitter with triarylamine
backbone
Hiroaki Itoi, Taehee Jang, Shinji Kanehashi, Takeshi Shimomura, Kenji Ogino
PII:
S0040-4039(17)30981-4
DOI:
http://dx.doi.org/10.1016/j.tetlet.2017.08.004
TETL 49194
Reference:
Tetrahedron Letters
To appear in:
Received Date:
Revised Date:
Accepted Date:
13 June 2017
29 July 2017
1 August 2017
Please cite this article as: Itoi, H., Jang, T., Kanehashi, S., Shimomura, T., Ogino, K., Synthesis and properties of a
new AIE macrocyclic emitter with triarylamine backbone, Tetrahedron Letters (2017), doi: http://dx.doi.org/
10.1016/j.tetlet.2017.08.004
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Tetrahedron Letters
journal homepage: www.els evier.com/loc ate/tetlet
Synthesis and properties of a new AIE macrocyclic emitter with triarylamine
backbone
Hiroaki Itoi a, Taehee Jang a, Shinji Kanehashi b, Takeshi Shimomura b, Kenji Ogino a,*
a Graduate School of Bio-Applications and Systems Engineering, Tokyo University of Agriculture and Technology, 2-24-16 Nakacho, Koganei, Tokyo 184-8588
b Graduate School of Engineering, Tokyo University of Agriculture and Technology, 2-24-16 Nakacho, Koganei, Tokyo 184-8588, Japan
ARTICLE INFO
ABSTRACT
Article history:
Received
A new macrocyclic AIE emitter composed of triarylamine backbone was successfully
synthesized through convenient homocoupling procedure and easily purified by silica gel
column chromatography, and recrystallization. The optical and electrochemical properties of the
compound have been investigated. Intriguingly, the compound shows dual emission both 423
nm and 505 nm. This result implied that the violet emission was originated from an isolated
component of the emitter, whereas the yellowish-green emission simultaneously exhibited AIE
nature. The compound exhibits enough thermal stability and high glass transition temperature to
be applied for organic devices.
Received in revised form
Accepted
Available online
Keywords:
Macrocycle
McMurry coupling
Aggregation-induced emission (AIE)
Triarylamine
2017 Published by Elsevier Ltd.
Dual emission
Introduction
poor.15 The ACQ problem can be solved easily by incorporation
of the TPE unit. A variety of TPE–TPA derivatives have been
Much kind of studies have been done on organic light-
emitting diodes (OLEDs), because they have a great potential to
be applied to large full-color displays.1-3 Traditional organic
luminophores are mainly composed of planar aromatic rings.
They emit efficiently in dilute solutions while being weakened or
even totally quenched due to the formation of detrimental
aggregates, which facilitate exciton interactions and nonradiative
pathways.4 In 2001, the group of B. Z. Tang reported
aggregation-induced emission (AIE), which is the phenomenon
making contrast with the aggregation-caused quenching (ACQ)
effect.5 Since the AIE effect is also observed in a film state, a lot
of AIE molecules have been synthesized, and the optical
properties of them have been investigated.6 In various
fluorophores, molecules having tetraphenylethene (TPE) unit
show a strong emission by AIE effect.7 Nowadays, many
researchers have developed a lot of efficient solid-state emitters
using TPE as the key building block because almost all TPEs are
easily synthesized and show distinguished AIE effect.8-10
Organic electroluminescent materials with multifunctional
properties, such as light-emitting and carrier-transporting abilities
are ideal for high-technological and practical applications
because they can simplify the device structure and reduce
fabrication cost. Triphenylamine (TPA) has been utilized widely
as an essential moiety as a building block of hole-transporting
materials since it affords high hole mobility in an amorphous
state.11-14 However, TPA derivatives also suffer from the ACQ
effect in the film state, which makes the device performance
developed and showed both good hole-transporting property and
high PL efficiency.16-19 Owing to the TPE unit, all the TPE–TPA
adducts show AIE features and emit intense sky blue to green
lights in solid films with high ΦF values up to unity. As the
orbital distributions of the HOMO and LUMO energy levels are
close to those of N,N′-di(1-naphthyl)-N,N′-diphenyl-(1,1′-
biphenyl)-4,4′-diamine (NPB), one of the most famous hole-
transporting materials, their hole-injection and transporting
abilities are preserved.
In the preparation of macrocyclic compounds, low isolated
yields often become crucial drawbacks in the practical view point.
Our research group reported the synthesis of cyclic oligomers
composed of triphenylamine via Pd catalyzed C-N coupling
reaction of A-B type monomer 20, where the cyclic pentamer was
isolated in an acceptable yield (11%) from the products
containing liner and cyclic (hexa- and heptamer) oligomers as
byproducts. However, it is generally difficult to remove cyclic
byproducts with different degree of oligomerization from the
crude products, and a time-consuming and complicated operation
such as gel permeation chromatography (GPC) is required.
Recently, Tohama et al. have developed an effective synthetic
method for macrocyclic arylethenes via McMurry coupling. 21 In
this report, we designed a cyclic oligotriphenylamine having TPE
unit. It is expected that the rigid cyclic structure of the compound
shows strong fluorescence emission preventing nonradiative
decay as well as high thermal stability. Hitherto, there is no
report on a macrocycle with TPA and TPE backbone.
∗ Corresponding author. Tel.: +81-42-388-7404; Fax: +81-42-388-7404; E-mail: kogino@cc.tuat.ac.jp

2
Results and discussion
from 3 via McMurry reaction in 1,4-dioxane in diluted
conditions to prevent forming liner polymeric byproducts.13 The
final reaction, homocoupling of the dog-leg shaped ketone
precursor 3 facilitates the formation of cyclic compound 4
without any cyclic byproduct. Actually, the yield of the final step
was 15% where compound 4 is purified only by column
chromatography and recrystallization. This result is a little bit
better than that via C-N coupling reaction using Buchwald-
Hartwig reaction reported by our group.20
n-Oct
I
Br
Pd2(dba)3, DPPF, tBuOK
n-Oct
N
NH2
Br
Br
Toluene, 120℃, 3 h
1 (61%)
n-Oct
O
O B
Figure 1a shows UV-vis absorption spectrum for compound
4. Compared with cyclic pentamer of 4-butyltriphenylamine, the
wavelength at absorption maximum (356 nm) is slightly blue-
shifted (8 nm). As shown in Figures 1b, the emission peak of
compound 4 is located at 505 nm in the film state. The absolute
quantum yield measured by an integrating sphere is 34.6% for
compound 4. However, the emission peak of compound 4 is
located at 423 nm for a dilute solution in THF. To investigate the
features of the compound, we measured PL spectra in THF/water
mixtures with different water fraction (fw). As expected, the
compound shows dual emission. Figure 2 shows the change of
PL spectra (a) and PL intensity dependence on water content
together with fluorescent images. When the water content is less
than 30%, compound 4 shows peaks at around 423 nm. At 50%
water content, the emission around 423 nm almost extincted, and
that around 505 nm appeared. As the water fraction (fw)
increases, the aggregates form step by step. At 70% of fw, the PL
intensity at around 505 nm is over 19.8 times that in pure THF.
On the other hand, at 10% of fw, the PL intensity at around 423
nm is over 23.8 times higher than that at 90%. This result implied
that the violet emission was from a single component of
compound 4, which was converted to an aggregation form with
the increase of fw, whereas the yellowish-green emission
simultaneously exhibited typical AIE nature.
O
n-BuLi
N
O
O
B
O
B
O
THF, -78℃, 2 h
2 (36%)
O
n-Oct
Br
Pd(PPh3)4, K3PO4
N
Toluene/EtOH/H2O, 80℃, 2 h
O
O
3 (92%)
n-Oct
N
Zn, TiCl4
Dioxane, 100℃, 18 h
N
In case of most TPE emitters, the restriction of the
intramolecular rotation (RIM) mechanism can be employed to
explain the enormous difference of fluorescence behavior
between solution state and solid state: the strong intermolecular
interactions in solid state can restrict the rotation of the phenyl
rings, which blocks the nonradiative channel, extends the
conjugation, and enhances the emission. However, in the THF
solution state of compound 4, the rigid conformation of the cyclic
structure, immobilizing the two phenyl groups in each of the TPE
units, has partially hampered the RIM process and hence makes it
emissive. Recently Zeng et al. reported a TPE based emissive
molecule in which two diacetylenes are induced to restrict the
rotation of phenyl rings in TPE, and consequently preserves the
fluorescence in the diluted solution.22 In the solid state, the RIM
n-Oct
4 (15%)
Scheme 1. Synthetic routes to compound 4.
The synthetic route for the target compound is depicted in
Scheme 1. In this process, an amine intermediate 1 was
synthesized from 4-n-octylaniline and 1-bromo-4-iodobenzene
using palladium catalyst. Compound 1 was subsequently reacted
with 2-isopropoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane to
afford a pinacol ester 2. A ketone intermediate 3 was synthesized
from compound 2 and 4-bromobenzophenone using Suzuki-
Miyaura cross coupling. The cyclic oligomer was synthesized
Scheme 1. Synthetic routes to compound 4.
Figure 1. (a) UV–vis spectrum of compound 4 in THF solution (2.0 × 10 −6 M). (b) Photoluminescence spectra of compounds 4 in solid film
and THF solution (2.0 × 10 −6 M). Excitation wavelength: 365 nm.

3
Table 1 Optical and electrochemical properties of compound 4
λabs (nm)
ΦF (%)b
HOMO (eV)c
LUMO (eV)
-2.60
Eg (eV)d
Compound
/
Tg Td
(°C)
Solutiona
356
Filmb
505
4
34.6
134/434
-5.55
2.95
a 2 × 10-6 M in THF solution.
b Film drop-casted on quartz plate.
c HOMO levels were investigated by cyclic voltammetry with a reference electrode of Ag/AgCl:
HOMO = - (Vox+V(Ag/AgCl vs SHE)+V(SHE vs vacuum)) = - (Vox+0.198+4.45).
d Estimated from the onset of the absorption spectra: 1240/λonest
.
Figure 2. (a) PL spectra of compound 4 in THF/water mixtures with different water fractions (fw). Inset: photo of compound 4 in THF/water
mixtures (fw = 0 and 90%) under UV lamp illumination. Excitation wavelength: 365 nm. (b) Emission peak intensity (I peak) of compound 4 in
THF and THF/water at varying fws at 423 nm and 505 nm. Concentration = 1.0 × 10−4 M.
process is further restricted, which shows red-shifted emission
because of the π-extension caused by the other two phenyl
groups in the TPE units (Figure3). The high planarity of 4 by the
cyclization causes π−π interaction to form excimer, and also
contributes to the red-shifted broad spectrum.23 In previous
studies, it’s already found that the RIM process can be activated
by many external factors, such as solvent viscosity, temperature,
pressure, etc.24-30 Rigidification of the conformation of TPE can
also effectively promote the RIM process leading to change its
emission behavior.
optical quality after 2 months. The electrochemical properties
were revealed by cyclic voltammetry (CV) measurements (Figure
S9). The measured data are summarized in Table 1. The energy
levels of the highest occupied molecular orbital (HOMO) of the
compound 4 was estimated from its oxidation potential according
to an empirical formula, EHOMO = - (Vox+0.198+4.45), whereas
the LUMO energy level was obtained from the optical band gap
energy (estimated from the onset wavelengths of the UV
absorption) and the HOMO level. The HOMO level for
compound 4 is −5.55 eV, suggesting that 4 has hole-transporting
ability due to the introduction of the triphenylamine unit. The
band gap was derived from the absorption edge in the absorption
spectrum with the value of 2.95 eV for 4. The LUMO value of
sample can be estimated by subtraction of the optical band gap
energy from the HOMO energy level with the value of −2.60 eV
for 4.
In conclusion, a macrocyclic compound 4 which bears
triphenylamine and tetraphenylethylene backbones has been
synthesized. The key preparation method for the
macrocyclization using McMurry reaction has been developed,
which gives a good conversion yield. The compound shows dual
emission because of AIE and the rigidness of 4. The compound
also exhibits a high thermal stability and glass transition
temperature, and the HOMO and LUMO values show suitable for
hole-transporting materials. This work provides an effective
method for preparation of the macrocyclic AIE material, which
has great potential for OLED applications, even in non-doped
emissive layer.
The thermal properties of compound 4 was investigated by
thermo-gravimetric (TG) and differential scanning calorimetry
(DSC) analyses as shown in Figures S4 and S5. The compound
shows high thermal decomposition temperature (Td; 434ºC).
Compound 4 shows glass transition at 156ºC. Due to the cyclic
rigid structure, compound
temperature (Tg) than other TPE compounds suitable for wet
processable electroluminescent devices, although
4 has higher glass transition
the
fluorescence quantum yield of 4 in the film state was moderate.16
In DSC thermogram, there is no other thermal transitions such as
a cold crystallization and a melting, indicative of amorphous
nature of 4. Indeed it is found that the thin film of 4 keeps the
n-Oct
n-Oct
N
N
N
N
n-Oct
n-Oct
λem = 505 nm
λem = 423 nm
(in solid state)
(in solution state)
Figure 3. Structure images of compound 4 in solution and solid state.

4
A. Supplementary data
1
Supplementary data (spectroscopic methods, such as H-, 13C-
NMR, mass spectroscopy and thermal properties with
satisfactory results obtained) associated with this article can be
found, in the online version, at http://.
References and notes
1.
2.
Tang C. W.; Vanslyke S. A. Appl. Phys. Lett. 1987, 51, 913.
Kim J. S.; Heo J.; Kang P.; Kim J. H.; Jung S. O.; Kwon S. K.
Macromol. Res. 2009, 17, 91.
3.
4.
5.
6.
7.
Park H. T.; Shin D. C.; Shin S. C.; Kim J. H.; Kwon S. K.; Kim Y. H.
Macromol. Res. 2011, 19, 965.
Thomas III S. W.; Joly G. D.; Swager T. M. Chem. Rev. 2007, 107,
1339.
Lee M. T.; Chen H. H.; Liao C. H.; Tsai C. H.; Chen C. H. Appl. Phys.
Lett. 2004, 85, 3301.
Chen J.; Xu B.; Ouyang X.; Tang B. Z.; Cao Y. J. Phys. Chem. A 2004,
108, 7522.
Dong Y.; Lam J. W. Y.; Qin A.; Liu J.; Li Z.; Tang B. Z. Appl. Phys.
Lett. 2007, 91, 011111.
8.
9.
Zhao Z.; Lam W. Y. J.; Tang B. Z. Mater. Chem. 2012, 22, 23726.
Zhao Z.; Lam S. C. J. W. Y.; Jim C. K. W.; Chan C. Y. K.; Wang Z.; Lu
P.; Kwok H. S.; Ma Y.; Tang B. Z. J. Phys. Chem. C, 2010, 114, 7963.
10. Zhao D. Z.; Chen S.; Shen X.; Mahtab F.; Yu Y.; Lu P.; Lam J. W. Y.;
Kwok H. S.; Tang B. Z. Chem. Commun., 2010, 46, 686.
11. Shirota Y. J. Mater. Chem. 2005, 15, 75.
12. Shirota Y.; Kageyama H. Chem. Rev. 2007, 107, 953.
13. Shirota Y. J. Mater. Chem. 2000, 10, 1.
14. Moorthy J. N.; Venkatakrishnan P.; Huang D.-F.; Chow T. J. Chem.
Commun. 2008, 2146.
15. Grimsdale D. A. C.; Chan K. L.; Martin R. E.; Jokisz P. G.; Holmes A.
B. Chem. Rev., 2009, 109, 897.
16. Liu Y.; Chen S.; Lam J. W. Y.; Lu P.; Kwok R. T. K.; Mahtab F.; Kwok
H. S.; Tang B. Z. Chem. Mater. 2011, 23, 2536.
17. Liu Y.; Chen X.; Lv Y.; Chen S.; Lam J. W. Y.; Mahtab F.; Kwok H.
S.; Tao X.; Tang B. Z. Chem.–Eur. J. 2012, 18, 9929.
18. Huang J.; Yang X.; Wang J.; Zhong C.; Wang L.; Qin J.; Li Z. J. Mater.
Chem. 2012, 22, 2478.
19. Yuan W.; Lu P.; Chen S.; Lam J. W. Y.; Wang Z.; Liu Y.; Kwok H. S.;
Ma Y.; Tang B. Z. Adv. Mater. 2010, 22, 2159.
20. Tsuchiya K.; Miyaishi H.; Ogino K. Chem. Lett. 2011. 40. 931.
21. Tohaya T.; Katagiri K.; Katoh J.; Masu H.; Tominaga M.; Azumaya I.
CrystEngComm 2010, 12, 3493.
22. Zeng F.; Zhao S.; Jiang Y.; Hu Z. Q. Tetrahedoron, 2017, 73, 4487.
23. Díez A.; Forniés J.; Fuertes S.; Lalinde E.; Larraz C.; López J. A.;
Martín A.; Moreno M. T.; Sicilia V. Organometallics, 2009, 28, 1705.
24. Hong Y.; Lam J. W. Y.; Tang B. Z. Chem. Comm., 2009, 4332.
25. Zhao Z.; Wang Z.; Lu P.; Chan C. Y. K.; Liu D.; Lam J. W. Y.; Sung H.
H. Y.; Williams I. D.; Ma Y.; Tang B. Z. Angew. Chem., Int. Ed., 2009,
48, 7608.
26. Li Z.; Liu Y.; Yu G.; Wen Y.; Guo Y.; Ji L.; Qin J.; Li Z. Adv. Funct.
Mater., 2009, 19, 2677.
27. Liu J.; Lam J. W. Y.; Tang B. Z. J. Inorg. Organomet. Polym. Mater.,
2009, 19, 249.
28. Hong Y.; Lam J. W. Y.; Tang B. Z. Chem. Soc. Rev., 2011, 40, 5361.
29. Qin A.; Lam J. W. Y.; Tang B. Z. Prog. Polym. Sci., 2012, 37, 182.
30. Zhao Z.; Lam J. W. Y.; Tang B. Z. Curr. Org. Chem., 2010, 14, 2109.

5
・A new macrocyclic AIE emitter composed of
triarylamine backbone was synthesized
・The optical and electrochemical properties of the
compound have been investigated.
・The compound shows dual emission both 423 nm
and 505 nm.
・The compound exhibits enough thermal stability
and high glass transition temperature.

6
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Synthesis and properties of a new AIE
macrocyclic emitter with triphenylamine
backbone
Hiroaki Itoi, Taehee Jang, Shinji Kanehashi,
Takeshi Shimomura, Kenji Ogino*