(Poly)terephthalates with Efficient Blue Emission in the Solid State

Article abstract of DOI:10.1002/asia.201801619

We prepared dimethyl and diaryl 2,5-dialkoxytere-phthalates from dimethyl 2,5-dihydroxyterephthalate in good-to-high yields via alkylation or a sequence of alkylation, hydrolysis, chlorination, and condensation. The absorption spectra of the dialkoxyterephthalates contain a small band at 332–355 nm, which could be assigned to intramolecular charge-transfer transition from the alkoxy to alkoxycarbonyl groups on the basis of theoretical calculations using density functional theory. The dialkoxyterephthalates exhibited blue fluorescence with moderate-to-excellent quantum yields not only in solution but also in the solid state, such as a poly(methyl methacrylate) (PMMA) film and a powder. The solid-state quantum yields of the diisopropoxy-substituted terephthalates were similar or considerably higher than those of the dimethoxy-substituted counterparts. Copolymerization of 2,5-diisopropoxyterephthaloyl chloride and 1,4-butanediol with or without terephthaloyl chloride gave brilliantly blue fluorescent polymers, whose quantum yields were 0.72 and 0.71 in toluene and 0.46 and 0.40 in the neat film, respectively. Furthermore, white emission was achieved when a fluorescent yellow 2,5-diaminoterephthalate was doped into the thin film of the blue fluorescent polymer at 0.4 wt %.

Full text of DOI:10.1002/asia.201801619

DOI: 10.1002/asia.201801619
Full Paper
(Poly)terephthalates with Efficient Blue Emission in the Solid State
Masaki Shimizu,*[a] Ryosuke Shigitani,[a] Takumi Kinoshita,[a] and Hiroshi Sakaguchi[b]
Abstract: We prepared dimethyl and diaryl 2,5-dialkoxytere-
phthalates from dimethyl 2,5-dihydroxyterephthalate in
good-to-high yields via alkylation or a sequence of alkyla-
tion, hydrolysis, chlorination, and condensation. The absorp-
tion spectra of the dialkoxyterephthalates contain a small
band at 332–355 nm, which could be assigned to intramo-
lecular charge-transfer transition from the alkoxy to alkoxy-
carbonyl groups on the basis of theoretical calculations
using density functional theory. The dialkoxyterephthalates
exhibited blue fluorescence with moderate-to-excellent
quantum yields not only in solution but also in the solid
state, such as a poly(methyl methacrylate) (PMMA) film and
a powder. The solid-state quantum yields of the diisopro-
poxy-substituted terephthalates were similar or considerably
higher than those of the dimethoxy-substituted counter-
parts. Copolymerization of 2,5-diisopropoxyterephthaloyl
chloride and 1,4-butanediol with or without terephthaloyl
chloride gave brilliantly blue fluorescent polymers, whose
quantum yields were 0.72 and 0.71 in toluene and 0.46 and
0.40 in the neat film, respectively. Furthermore, white emis-
sion was achieved when a fluorescent yellow 2,5-diaminoter-
ephthalate was doped into the thin film of the blue fluores-
cent polymer at 0.4 wt%.
Introduction
sufficient for commercial use. In addition, precious metal com-
plexes generally experience concentration quenching, which
limits their use as blue dopants. Considering that blue-emissive
materials can serve as not only blue emitters but also host ma-
terials for dopants that emit in the longer wavelength region
than blue light, the development of blue fluorescent materials
that overcome aggregation-caused quenching (ACQ) is cru-
cial.[8]
The creation of organic small molecules that efficiently fluo-
resce in the solid state is an important research subject in the
field of functional molecular materials.[1] This is because the
creation of such novel fluorophores would lead to advances in
organic solid-state light-emitting devices, such as organic light-
emitting diodes (OLEDs),[2] organic light-emitting field effect
transistors,[3] and semiconducting lasers.[4] In the fields of not
only OLEDs but also bio- and molecular sensing, conjugated
polymers that exhibit efficient fluorescence in film have also at-
tracted much attention.[5] Therefore, the design of fluorescent
small molecules that can be developed into luminescent poly-
mer films is considered of significant value.
We have previously demonstrated that 2,5-diaminotereph-
thalic acid diesters 1a and dithioesters 1b exhibit efficient
green-to-yellow and orange-to-red fluorescence in the solid
state, respectively (Scheme 1).[9] The key to the efficient solid-
state emissions is the ortho-arrangement of the donors (amino
groups) and acceptors (carbonyl moieties), as well as the intra-
molecular charge-transfer (ICT) from the donors to the accept-
Blue fluorescent materials with high efficiency in the solid
state are particularly desired in the field of OLEDs.[6] Because
the internal quantum efficiency of phosphorescent OLEDs is
100%, extensive research has been carried out on the develop-
ment of phosphorescent organometallic complexes containing
precious metals, such as iridium and platinum.[7] However, the
lifetimes of OLEDs using such blue-emissive complexes are not
[a] Prof. M. Shimizu, R. Shigitani, T. Kinoshita
Faculty of Molecular Chemistry and Engineering
Kyoto Institute of Technology
1 Hashikami-cho, Matsugasaki, Sakyo-ku, Kyoto 606-8585 (Japan)
E-mail: mshimizu@kit.ac.jp
[b] Prof. H. Sakaguchi
Institute of Advanced Energy
Kyoto University
Gokasho, Uji, Kyoto 611-0011 (Japan)
Supporting information and the ORCID identification number(s) for the au-
thor(s) of this article can be found under:
https://doi.org/10.1002/asia.201801619.
This manuscript is part of a special issue on p-Conjugated Compounds for
Molecular Materials. A link to the Table of Contents of the special issue will
appear here when the complete issue is published.
Scheme 1. Molecular structures of fluorescent (poly)terephthalates 1–3.
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ors. The ortho-arrangement-induced twisted molecular confor-
mation results in the suppression of dense packing in the solid
state, thereby inhibiting intermolecular electronic communica-
tion via the Dexter mechanism. The ICT results in a large
Stokes shift, which reduces the loss of the excited energy via
the Fçrster mechanism. In cases of organic luminophores
whose excitation processes involve ICTs, the emission maxi-
mum can be hypochromically or bathochromically shifted by
weakening or strengthening the degree of ICT character by the
appropriate combination of donor and acceptor.[10] Thus, we
designed 2,5-dialkoxyterephthalates 2 in which the amino
groups in 1a are replaced by less electron-donating alkoxy
groups for use as ACQ-free blue emitters.[11] We further expect-
ed that the development of blue fluorescent terephthalates
would lead to the development of blue luminescent polyter-
ephthalates. Indeed, we confirmed the validity of the molecu-
lar design. Here, we report the preparation, photophysical
properties, structures, and theoretical study of blue-emissive 2
and 2-based blue fluorescent polyesters 3, which may serve as
coating emitting layers for OLEDs.
the corresponding phenol derivatives. Although the decompo-
sition temperatures (Td), which is defined as the temperature
at which 5% mass is lost, of 2aa and 2ba were less than
1708C, diaryl esters 2ab–2ae and 2bb–2be were thermally
stable, and their Td values ranged from 225 to 2738C (as
shown in the Experimental Section).
Photophysical properties
UV absorption data of 2 in toluene are listed in Table 1, and se-
lected spectra are shown in Figure 1 (for spectra of 2ba–2be,
refer Figure S1). The absorption maxima (labs) appeared at
332–355 nm with small molar absorption coefficients (e), rang-
ing from 4000 to 7100mÀ1 cmÀ1, which can be assigned to ICTs
Table 1. Absorption maxima and molar absorption coefficients of 2 in
toluene.[a]
2
labs [nm]
e [mÀ1 cmÀ1
]
2
labs [nm]
e [mÀ1 cmÀ1
]
2aa
2ab
2ac
2ad
2ae
337
345
345
343
355
4600
5500
6200
7100
5600
2ba
2bb
2bc
2bd
2be
332
342
347
341
353
4000
4700
4800
4800
4900
Results and Discussion
[a] 1.0ꢁ10À4 m.
Synthesis of 2,5-dialkoxyterephthalates 2
Dialkoxyterephthalates 2 were prepared from dimethyl 2,5-di-
hydroxyterephthalate (Scheme 2).[12] Alkylation of the dihydrox-
yterephthalate with methyl iodide or isopropyl iodide gave di-
methyl esters 2aa and 2ba in 92% and 95% yields, respective-
ly. Diaryl terephthalates 2ab-2ae and 2bb-2be were synthe-
sized from 2aa and 2ba, respectively, in good-to-excellent
yields through hydrolysis with LiOH, chlorination with SOCl2,
and esterification with phenol derivatives. We chose the sub-
stituents R2 listed in Scheme 2 in view of the salient differences
of electronic and steric effects, and the readily availability of
Figure 1. Absorption spectra of 2 in toluene.
from the alkoxy to alkoxycarbonyl groups (refer Theoretical cal-
culations). The differences in the absorption maxima between
each methoxy-substituted derivative 2a and the correspond-
ing isopropoxy-substituted derivative 2b are less than 6 nm
(for example, compare 2aa and 2ba). Meanwhile, with respect
to 2aa or 2ba, the absorption maxima of 2ab–2ae or 2bb–
2be were red-shifted by 6–18 or 9–21 nm, respectively. In
other words, the highest occupied molecular orbital (HOMO)-
lowest unoccupied molecular orbital (LUMO) energy gaps of
the diaryl esters are narrower than those of the dialkyl esters.
These results indicate that the effect of the alkyl or alkoxy sub-
stituent at the central benzene ring on the energy gap of the
HOMO and LUMO is small, and the ICT characters of the diaryl
esters 2ab–2ae and 2bb–2be are stronger than those of the
dimethyl esters 2aa and 2ba. Because the absorption maxima
Scheme 2. Synthesis of 2,5-dialkoxyterephthalates 2.
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of 1 appeared at much longer wavelengths (for example, labs
=
thin film of poly(methyl methacrylate) (PMMA), having quan-
tum yields of 0.19–0.64 (Table 2). The powder of 2 also exhibit-
ed blue fluorescence with moderate-to-excellent quantum
yields (Table 2 and Figure 3, and for spectra of 2ba–2be, refer
415 nm for dimethyl 2,5-bis(diphenylamino)terephthalate),[9a]
the ICT character of 2 is, as expected, weaker than that of 1.
All molecules of type 2 in toluene exhibited blue fluores-
cence with emission maxima in the range of 402–434 nm in
moderate-to-excellent quantum yields (F=0.31–0.95), except
for 2ad (F=0.08) (Table 2). The fluorescence spectra of 2aa-
2ae and 2ba are shown in Figure 2 (for spectra of 2ba–2be,
Table 2. Fluorescence data of 2.[a]
2
lem [nm] (F)[b]
In toluene[c]
In PMMA film
In powder[d]
2aa
2ab
2ac
2ad
2ae
2ba
2bb
2bc
2bd
2be
402 (0.57)
418 (0.54)
422 (0.76)
415 (0.08)
428 (0.95)
410 (0.69)
425 (0.70)
429 (0.87)
423 (0.31)
434 (0.88)
402 (0.33)
418 (0.30)
418 (0.38)
410 (0.19)
422 (0.57)
409 (0.57)
422 (0.56)
428 (0.64)
422 (0.42)
431 (0.59)
413 (0.36)
437 (0.22)
426 (0.65)
420 (0.18)
426 (0.81)
413 (0.63)
420 (0.58)
425 (0.64)
416 (0.51)
431 (0.75)
Figure 3. Fluorescence spectra of 2aa–2ae, 2ba, and 2be in powders.
Figure S5).[14] Because the quantum yields of diisopropoxy de-
rivatives 2ba–2be were similar or much higher than those of
dimethoxy derivatives 2aa–2ae, the choice of a bulkier alkyl
group as substituent R1 in 2 is beneficial for attaining the
solid-state fluorescence of 2 with high efficiency. The differen-
ces in the emission peak wavelengths between the samples in
toluene and those in powder form were generally small, sug-
gesting that the intermolecular electronic communications be-
tween each molecule of 2 in the solid state were weak, which
is another reason for the efficient solid-state blue emission.
Full-widths at half maxima (fwhm) of fluorescence spectra of 2
in powder were smaller than those in toluene, which was rare
phenomenon. Considering the weak intermolecular electronic
interactions of 2 in powder, the narrower emission bands of
the powders are presumably ascribed to the smaller conforma-
tional variations in powder than those in solution. The quan-
tum yields of the 2,5-dimethylphenyl esters 2ad and 2bd were
the lowest compared with those of the others in any state. The
electron-rich nature of 2,5-dimethylphenyl group, the steric
effect of a methyl group at 2-position of the benzene ring,
which force to make the benzene ring orthogonal to the car-
bonyl plane (as confirmed by X-ray crystallography of 2bd), or
both may destabilize the excited states of 2ad and 2bd.
[a] Excited at 320 nm. [b] F: Absolute quantum yield determined using
the calibrated integrating sphere system. [c] 1.0ꢁ10À4 m. [d] Semicrystal-
line powder.
Figure 2. Fluorescence spectra of 2aa–2ae, 2ba, and 2be in toluene.
refer Figure S2). The relatively large Stokes shifts (65–83 nm)[13]
of 2 in toluene imply that the structural difference between
the ground and lowest singlet excited states is significant be-
cause of the ICT, and the spectral overlap between absorption
and fluorescence is small, which is beneficial for diminishing
the probability of Fçrster-type energy transfer from the lowest
singlet excited state. As observed in the absorption maxima,
the emission maxima of the diaryl esters were red-shifted com-
pared to those of dimethyl esters. In the series of diaryl esters,
substitution of electron-withdrawing or -donating groups, that
is, CF3 or CH3, into the phenyl rings as R2 resulted in batho-
chromic or hypochromic shift of the spectra, respectively, com-
pared with that of unsubstituted 2ab or 2bb. Changing
methyl groups as R1 to isopropyl groups induced red-shift (for
example, compare 2aa and 2ba). Similar fluorescence spectra
(Figures S3 and S4) were observed when 2 was dispersed in a
X-ray crystallography
Single crystals of 2ac and 2bd suitable for X-ray diffraction
analysis were obtained by recrystallization from a solution of
CH2Cl2/hexane.[15] The molecular and crystal structures of 2ac
and 2bd are shown in Figures 4 and 5, respectively. Each mole-
cule of 2ac and 2bd is centrosymmetric with an inversion
center at the centroid of the central benzene ring. As shown in
Figure 4a, the methyl carbons of 2ac are located in the same
plane as the central benzene ring (C1-O1-C2-C3=4.168). The
dihedral angle between the carbonyl group of 2ac and the
central benzene ring (C2-C4-C5-O2) is 11.398. Thus, the carbon-
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Figure 4. Molecular (a) and crystal (b) structures of 2ac (hydrogen atoms are
omitted for clarity). Each molecule in (b) is color-coded based on symmetry
operations.
Figure 5. Molecular (a) and crystal (b) structures of 2bd (hydrogen atoms
are omitted for clarity). Each molecule in (b) is color-coded based on sym-
metry operations.
yl groups are not significantly twisted with respect to the cen-
tral benzene ring, irrespective of the ortho-arrangement of car-
bonyl and methoxy groups. In turn, the CF3-substituted phenyl
groups are oriented almost perpendicular to the carbonyl
planes (C5-O3-C6-C7=87.318). Probably because of the twisted
molecular structure, there is no p-p stacking between the fluo-
rescent cores in the crystal of 2ac (Figure 4b), which is advan-
tageous for preventing the loss of the excited energy via the
Dexter mechanism and for the highly efficient solid-state fluo-
rescence of 2ac (F=0.65).
In the case of 2bd, the dihedral angles between the central
benzene ring, and the methine carbon of the isopropyl group
and a carbonyl group are 27.798 (C1-O1-C2-C3) and 42.348 (C5-
C4-C6-O2), respectively (Figure 5a). Thus, the two isopropyl
and two carbonyl groups are significantly distorted from the
plane of the central benzene ring as expected. The 2,5-dime-
thylphenyl groups are almost orthogonal to the carbonyl plane
(C6-O3-C7-C8=86.128). As shown in Figure 5b, 2bd, which has
a fully twisted molecular framework, forms a loosely packed
crystal with no p-p stacking, resulting in the efficient solid-
state emission of 2bd (F=0.51).
Figure 6. Frontier molecular orbitals and their energies of 2ac and 2bd.
ergies are illustrated in Figure 6. The HOMOs are delocalized
over the central benzene ring and the ethereal oxygen atoms,
while the LUMOs are concenrated on the central benzene ring
and carbonyl groups. Time-dependent DFT (TD-DFT) calcula-
tions of 2ac and 2bd showed that the lowest energy transi-
tions correspond to the HOMO–LUMO transitions with coeffi-
cients of 0.699 and 0.697, and oscillator strengths of 0.1323
and 0.1529, respectively. Hence, the weak absorption peaks of
2 at 332–355 nm can be assigned to the ICT from the alkoxy
to alkoxycarbonyl groups.
Theoretical calculations
To confirm the ICT in the excitation process of 2, frontier orbi-
tal calculations of 2ac and 2bd were carried out using the
density functional theory (DFT) at the B3LYP/cc-pVDZ level of
theory using the Gaussian 09 package.[16] The structural optimi-
zations were performed with the initial geometries determined
by X-ray diffraction analysis. The HOMOs, LUMOs, and their en-
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Blue-fluorescent polymers
Polyesters made from terephthalic acid and aliphatic diols such
as polyethylene terephthalate (PET) and polybutylene tereph-
thalate (PBT) constitute a class of versatile engineering plas-
tics.[17] Because we have succeeded the development of ter-
ephthalates showing efficient solid-state blue fluorescence, we
envisioned that polyesters consisting of dialkyl 2,5-dialkoxyter-
ephthalate framework could be efficient blue fluorescent poly-
mers in the neat films.[18] Because we observed that the quan-
tum yields of 2ba were higher than those of 2aa (Table 2), we
chose an isopropoxy group as the alkoxy group. Then, 2,5-dii-
sopropoxyterephthaloyl chloride (4) was polymerized with 1,4-
butanediol in the absence or presence of terephthaloyl chlo-
ride (5) in CH2Cl2 using pyridine as a base to produce 3a or 3b
in 59% or 56% yield, respectively (Scheme 3). The glass transi-
tion temperatures of polymer 3a and 3b were 71 and 158C,
respectively. Hence, the incorporation of 5 as the second mo-
nomer into 3a resulted in the lowering of the glass transition
temperature.
Figure 7. Fluorescence spectra of 3a and 3b in toluene and neat film, and
their fluorescent images upon irradiation using a UV lamp (365 nm).
and fluoresced with slightly red-shifted spectra with respect to
those in toluene.[19] Although the fluorescence quantum yields
in neat films of 3a and 3b were slightly lower than that of
2ba in PMMA, it is valuable that polymers 3a and 3b in film
was demonstrated to exhibit blue fluorescence with good
quantum yields in view that a new molecular design principle
for blue-luminescent polymers is provided. Very recently,
Zhang, Yuan, and co-workers reported that poly(ethylene ter-
ephthalate) exhibit aggregation-induced emission in solids.[20]
The emission mechanism involves the formation of terephtha-
late clusters leading to excimer emission, which is completely
different from the mechanism of 2.[21]
Furthermore, to demonstrate the potential of 3b as a host
blue-emitting polymer for white emissions,[22] we prepared
spin-coated films of 3b doped with the yellow fluorescent di-
methyl 2,5-bis[bis(4-tert-butylphenyl)amino]terephthalate (6).[9a]
The reason that we chose 6 as the dopant was that the CIE co-
ordinates of 6 in the PMMA film are (x=0.43, y=0.55); thus,
they are approximately located on the line penetrating the CIE
coordinates of blue-emissive film 3b (x=0.16, y=0.05) and
ideal white emission (x=0.33, y=0.33) (Figure S7). The molec-
ular weight ratios of 3b and 6 were varied from 500:1 to
250:1, and the photoluminescent properties of the 6-doped
films of 3b are summarized in Table S2, and the spectra are
shown in Figure S8. The film consisting of 3b and 6 in a ratio
of 250:1 exhibited almost ideal white emission (CIE coordinate:
x=0.32, y=0.34) with a quantum yield of 0.43. The spectrum
and luminescence image of the white-emissive film are shown
in Figure 8 along with the spectra of 3b in film and 6 in
PMMA film.
Scheme 3. Synthesis of poly(2,5-dialkoxyterephthalate)s 3.
The photophysical properties of 3a and 3b are summarized
in Table 3. Their absorption spectra are completely overlapped
at 300–400 nm and almost identical with that of 2ba (Fig-
ure S6). Toluene solutions of 3a and 3b exhibited efficient
blue fluorescence at the emission maxima of 413 and 414 nm
with quantum yields of 0.71 and 0.72, respectively (Figure 7).
Neat thin films of 3a and 3b were prepared by spin-coating
Table 3. Photophysical properties of 3.
3
Absorption
lmax [nm]
In toluene
Fluorescence[a]
lem [nm] (F)[b]
In toluene
In neat film[c]
3a
3b
334
335
413 (0.71)
414 (0.72)
418 (0.40)
420 (0.46)
Conclusions
[a] Excitation was effected at 320 nm. [b] F: Absolute quantum yield de-
termined using the calibrated integrating sphere system. [c] Prepared by
spin-coating.
We developed 2,5-dialkoxyterephthalates, which are readily
prepared from commercially available chemicals via facile
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using Merck’s Kieselgel 60 (230–400 mesh). Reagent-grade CH2Cl2
and THF were passed through two packed columns of neutral alu-
mina and copper oxide under a nitrogen atmosphere before use.
All reactions were carried out under an argon atmosphere.
Measurement of absorption and photoluminescence spectra
The spectroscopic-grade toluene for photoluminescence measure-
ments was purchased from Kanto Chemical Co., Inc. and degassed
with argon before use. UV-visible absorption spectra were mea-
sured with a Shimadzu UV-2550 spectrometer. Luminescence spec-
tra and absolute quantum yields were recorded with a Hamamatsu
Photonics C9920-02 Absolute PL Quantum Yield Measurement
System.
Figure 8. Fluorescence spectra of 3b in film, 6 in PMMA film, and 6-doped
3b in film, and the fluorescent image of the doped film of 3b.
Preparation of 2-doped PMMA film
In a glass tube, 2 (1.0 mg) was placed and dissolved in a toluene
solution of PMMA (99 mg in 1 mL). The resulting solution was
dropped onto a quartz plate (10 mmꢁ10 mm) and spin-coated at
300 rpm for 40 s and then at 1000 rpm for 60 s. The 2-doped
PMMA film was dried under vacuum at room temperature for 3 h.
chemical transformations, as blue luminophores that efficiently
fluoresce in the solid state, such as polymer films and powders.
In addition, we confirmed that poly(2,5-diisopropoxyterephtha-
late)s consisting of the developed blue-emissive luminogen ex-
hibited efficient blue fluorescence as a neat film, and the blue-
emissive film effectively serves as a host polymer for white
emission that is useful for lighting applications. Considering
that polyterephthalates are valuable thermoplastic elastomers
with superior properties, such as high solvent-resistance, high
mechanical strength, and high insulating performance, the
present findings could contribute to the creation of polymeric
materials that unite luminescence with the merits of polyter-
ephthalates. Furthermore, considering that 2,5-diaminotereph-
thalic acid di(thio)esters serve as efficient solid-state emitters,
the present results clearly implied that 2,5-bis(donor)-substitut-
ed terephthalate frameworks are promising platforms for the
development of highly luminescent organic solids, which may
serve as coating emitting layers for OLEDs.
Preparation of neat film of 3
In a glass tube, 3 (10 mg) was placed and dissolved in CH2Cl2
(0.1 mL). The resulting solution was dropped onto a quartz plate
(10 mm x 10 mm) and spin-coated at 300 rpm for 40 s and then at
1000 rpm for 60 s. The neat film was dried under vacuum at room
temperature for 3 h.
Preparation of white-emissive 6-doped thin film of 3b
In a glass tube, 3b (2.0 mg) was placed and dissolved in a CH2Cl2
solution of 6 (0.16 gLÀ1, 50 mL). The resulting solution was dropped
onto a quartz plate (10 mm x 10 mm) and spin-coated at 300 rpm
for 40 s and then at 1000 rpm for 60 s. The 6-doped thin film was
dried under vacuum at room temperature for 3 h.
Synthesis of 2
Experimental Section
Preparation of 2aa: A 200 mL round-bottomed flask was charged
with dimethyl 2,5-dihydroxyterephthalate (2.3 g, 10.0 mmol), K2CO3
(4.1 g, 30 mmol), iodomethane (1.9 mL, 30 mmol), and acetone
(50 mL). The solution was refluxed for 48 h. The precipitate was re-
moved by filtration and washed with acetone. The filtrate was con-
centrated by using a rotary evaporator, and the residue was dis-
solved in CH2Cl2 (50 mL). The organic layer was washed with water
three times (50 mL), dried over anhydrous MgSO4, and concentrat-
ed in vacuo. The crude product was purified by recrystallization
from a CH2Cl2/hexane solution to give 2aa (2.3 g, 9.2 mmol, 92%)
as colorless solid. 2aa: Rf =0.11 (hexane/EtOAc 5:1); mp 1408C; Td:
1628C; 1H NMR (CDCl3, 400 MHz): d=3.90 (s, 6H), 3.92 (s, 6H),
7.40 ppm (s, 2H); 13C NMR (CDCl3, 100 MHz): d=52.5, 56.7, 115.4,
123.9, 152.3, 165.9 ppm; IR (KBr): n˜ =3017, 2907, 1715, 1682, 1634,
1505, 1427, 1308, 1238, 1105, 943, 827, 779, 698 cmÀ1; HRMS (FAB):
m/z calcd for C12H14O6: 254.0790 [M+]; found: 254.0797.
General
Melting and decomposition points were determined with a Seiko
1
Instrument Inc. TG/DTA6200. H NMR spectra were measured with
a Varian Mercury 400 (400 MHz) spectrometer. The chemical shifts
1
of H NMR signals are expressed in parts per million downfield rela-
tive to the internal tetramethylsilane standard (d=0 ppm). Split-
ting patterns are indicated as s, singlet; d, doublet; sept, septet; or
m, multiplet. 13C NMR spectra were measured with a Varian Mercu-
ry 400 (100 MHz) spectrometer with tetramethylsilane as an inter-
nal standard (d=0 ppm). 19F NMR spectra were measured with a
Bruker Avance II 300 (282 MHz) spectrometer with hexafluoroben-
zene as an internal standard (d=À163.7 ppm). Chemical shift
values are given in parts per million downfield relative to the inter-
nal standards. Infrared spectra (IR) of 2 were recorded on a Shi-
madzu FTIR-8400 spectrometer. IR attenuated total reflectance
(IRATR) spectra of 3 were recorded by using a Shimadzu FTIR-8400
spectrometer equipped with a Specac Quest ATR diamond acces-
sory. Fast atom bombardment, high-resolution mass spectrometry
(FAB-HRMS) analyses were performed with a JEOL JMS-700 spec-
trometer. TLC analyses were performed using Merck Kieselgel 60
F254 silica plates. Silica gel column chromatography was carried out
Compound 2ba was prepared in 95% yield as colorless solid in
the same procedure as for 2aa except for use of 2-iodopropane
(2.5 mL, 25 mmol) and Cs2CO3 (8.1 g, 25 mmol) in place of iodome-
thane and K2CO3, respectively. 2ba: Rf =0.32 (hexane/EtOAc 5:1);
mp 858C; Td 1658C; 1H NMR (CDCl3, 400 MHz): d=1.34 (d, J=
6.0 Hz, 12H), 3.90 (s, 6H), 4.50 (sep, J=6.0 Hz, 2H), 7.36 ppm (s,
2H); 13C NMR (CDCl3, 100 MHz): d=22.1, 52.2, 73.2, 119.5, 126.0,
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150.8, 166.3 ppm; IR (KBr): n˜ =2980, 1722, 1680, 1472, 1333, 1142,
966, 829, 783, 667 cmÀ1; HRMS (FAB): m/z calcd for C16H22O6:
310.1416 [M+]; found: 310.1425.
2bb: Rf =0.30 (CHCl3), mp 1278C; Td 2498C; 1H NMR (CDCl3,
400 MHz): d=1.40 (d, J=6.0 Hz, 12H), 4.64 (sep, J=6.0 Hz, 2H),
7.24–7.31 (m, 4H), 7.45 (t, J=8.0 Hz, 4H), 7.58 ppm (s, 2H);
13C NMR (CDCl3, 100 MHz): d=22.1, 73.0, 119.3, 121.7, 125.7, 126.0,
129.5, 150.8, 151.2, 164.4 ppm; IR (KBr): n˜ =2974, 1724, 1591, 1483,
1329, 1209, 1134, 1005, 918, 814, 787, 615 cmÀ1; HRMS (FAB): m/z
calcd for C26H27O6: 435.1808 [M+ +H]; found: 435.1798.
Typical procedure for preparation of 2ab–2ae and 2bb–2be: To a
200 mL round-bottomed flask charged with 2aa (1.8 g, 7.0 mmol)
and THF (20 mL) was added aqueous solution prepared from
LiOH·H2O (1.2 g, 28.0 mmol) and water (7 mL) at room tempera-
ture. The resulting solution was refluxed for 4 h. The precipitate
was removed by filtration, and HCl aq. (6m) was added to the fil-
trate until the solution became acidic. The generated precipitate
was collected by suction filtration and dried at 808C under
vacuum for 10 h, giving rise to 2,5-dimethoxyterephthalic acid as
colorless solid quantitatively, which was used for the next step
without further purification. To a 20 mL Schlenk flask was added
2,5-dimethoxyterephthalic acid (0.25 g, 1.0 mmol). The flask was
evacuated and filled with argon. This evacuation-purge operation
was repeated twice before adding CH2Cl2 (3 mL) and DMF (one
drop). To the solution was slowly added SOCl2 (0.22 mL, 3.0 mmol)
at 08C. The resulting mixture was heated at reflux for 2 h. Organic
solvent was removed by evaporation under vacuum to give 2,5-di-
methoxyphthaloyl chloride as yellow solid, which was used for the
next step without further purification. To the flask was added
PhOH (0.23 g, 2.5 mmol), catalytic amount of DMAP, and CH2Cl2
(5 mL) at room temperature. After cooling at 08C, pyridine
(0.40 mL, 5.0 mmol) was slowly added to the mixture. The solution
was heated at reflux for 12 h before quenching with ice-cooled HCl
aq. (1m, 5 mL). The reaction mixture was washed with water
(30 mLꢁ3), and the combined aqueous layer was extracted with
CH2Cl2 (50 mL). The organic solvent was dried over anhydrous
MgSO4 and removed by vacuum evaporation. The crude product
was purified by silica gel column chromatography to give 2ab
(0.36 g, 0.96 mmol, 96%) as colorless solid. 2ab: Rf =0.39 (hexane/
EtOAc 2:1); mp 1668C; Td 2508C; 1H NMR (CDCl3, 400 MHz): d=
3.97 (s, 6H), 7.24–7.30 (m, 4H), 7.45 (t, J=8.0 Hz, 4H), 7.64 ppm (s,
2H); 13C NMR (CDCl3, 100 MHz): d=56.9, 115.9, 121.7, 123.8, 126.1,
129.5, 150.7, 153.0, 163.8 ppm; IR (KBr): n˜ =3015, 1703, 1493, 1302,
1229, 1161, 1065, 920, 862, 779, 689 cmÀ1; HRMS (FAB): m/z calcd
for C22H19O6: 379.1182 [M+ +H]; found: 379.1183.
2bc: Rf =0.60 (CHCl3); mp 1748C; Td 2518C; 1H NMR (CDCl3,
400 MHz): d=1.40 (d, J=6.0 Hz, 12H), 4.65 (sep, J=6.0 Hz, 2H),
7.38 (d, J=8.4 Hz, 4H), 7.58 (s, 2H), 7.73 ppm (d, J=8.4 Hz, 4H);
13C NMR (CDCl3, 100 MHz): d=22.1, 73.0, 119.1 (q, 3JC-F =3.8 Hz),
2
122.2, 123.8 (q, 1JC-F =269.9 Hz), 125.2, 126.9, 128.3 (q, JC-F
=
32.8 Hz), 151.2, 153.3, 163.7 ppm; 19F NMR (CDCl3, 282 MHz): d=
À64.2 ppm; IR (KBr): n˜ =2992, 1713, 1601, 1414, 1377, 1227, 1067,
964, 835, 725, 677 cmÀ1; HRMS (FAB): m/z calcd for C28H25F6O6:
571.1555 [M+ +H]; found: 571.1546.
2bd: Rf =0.44 (hexane/EtOAc 5:1); mp 1328C; Td 2738C; 1H NMR
(CDCl3, 400 MHz): d=1.39 (d, J=6.0 Hz, 12H), 2.24 (s, 6H), 2.36 (s,
6H), 4.65 (sep, J=6.0 Hz, 2H), 6.98 (s, 2H), 7.01 (d, J=8.0 Hz, 2H),
7.17 (d, J=8.0 Hz, 2H), 7.58 ppm (s, 2H); 13C NMR (CDCl3,
100 MHz): d=16.0, 21.0, 22.1, 72.7, 119.0, 122.4, 125.6, 127.0, 130.9,
137.0, 149.3, 151.0, 164.3 ppm; IR (KBr): n˜ =2920, 1728, 1694, 1506,
1451, 1356, 1292, 1140, 993, 843, 719, 667 cmÀ1; HRMS (FAB): m/z
calcd for C30H35O6: 491.2434 [M+ +H]; found: 491.2439.
1
2be: Rf =0.41 (hexane/EtOAc 10:1); mp 1318C; Td 2258C; H NMR
(CDCl3, 400 MHz): d=1.42 (d, J=6.0 Hz, 12H), 4.68 (sep, J=6.0 Hz,
2H), 7.60 (s, 2H), 7.75 (s, 4H), 7.83 ppm (s, 2H); 13C NMR (CDCl3,
3
100 MHz): d=22.1, 72.9, 118.8 (q, JC-F =3.8 Hz), 119.9, 122.7, 122.8
(q, 1JC-F =271.4 Hz), 124.5, 133.1 (q, 2JC-F =34.3 Hz), 151.3, 151.4,
163.2 ppm; 19F NMR (CDCl3, 282 MHz): d=À64.9 ppm; IR (KBr): n˜ =
2993, 1753, 1223, 1186, 1001, 937, 826, 754, 667 cmÀ1; HRMS (FAB):
m/z calcd for C30H22F12O6: 706.1225 [M+]; found: 706.1226.
Synthesis of 3
3a: To an 80 mL Schlenk flask was charged with 2,5-diisopropoxy-
terephthaloyl chloride (4, 0.19 g, 0.6 mmol) prepared from 2ba.
The flask was evacuated and filled with argon. This evacuation-
purge operation was repeated twice before adding CH2Cl2 (6 mL)
and 1,4-butandiol (53 mL, 0.6 mmol). To this solution was slowly
added pyridine (0.19 mL, 2.4 mmol) at 08C, and the resulting solu-
tion was stirred for 3 h at room temperature before quenching
with HCl aq. (1m). The reaction mixture was diluted with CH2Cl2
(50 mL), and the organic layer was washed with HCl aq. (1m,
20 mL), sat. NaHCO3 aq. (20 mL), and sat. NaCl aq. (20 mL), and
dried over anhydrous MgSO4. The organic solvent was removed by
vacuum evaporation to give the crude product, which was dried
under vacuum and purified by GPC (eluent: CHCl3) and reprecipita-
tion from CH2Cl2 and MeOH, giving rise to 3a (0.12 g, 59%) as col-
orless solid. 3a: Mn 3850; Mw 5250; PDI 1.36 (polystyrene standard);
2ac: Rf =0.66 (hexane/EtOAc 2:1); mp 2078C; Td 2588C; 1H NMR
(CDCl3, 400 MHz): d=3.99 (s, 6H), 7.39 (d, J=8.4 Hz, 4H), 7.64 (s,
2H), 7.72 ppm (d, J=8.4 Hz, 4H); 13C NMR (CDCl3, 100 MHz): d=
3
1
56.9, 115.9 (q, JC-F =3.8 Hz), 122.3, 123.4, 123.8 (q, JC-F =270.6 Hz),
126.9, 128.4 (q, 2JC-F =32.8 Hz), 153.1, 153.2, 163.2 ppm; 19F NMR
(CDCl3, 282 MHz): d=À64.2 ppm; IR (KBr): n˜ =3078, 2943, 1742,
1611, 1505, 1414, 1385, 1236, 1072, 959, 841, 723, 667 cmÀ1; HRMS
(FAB): m/z calcd for C24H17F6O6: 515.0929 [M+ +H]; found:
515.0927.
2ad: Rf =0.43 (hexane/EtOAc 4:1); mp 1478C; Td 2668C; 1H NMR
(CDCl3, 400 MHz): d=2.24 (s, 6H), 2.35 (s, 6H), 3.97 (s, 6H), 7.00 (s,
2H), 7.01 (d, J=7.6 Hz, 2H), 7.17 (d, J=7.6 Hz, 2H), 7.64 ppm (s,
2H); 13C NMR (CDCl3, 100 MHz): d=15.9, 20.9, 56.8, 115.8, 122.4,
123.9, 126.9, 130.9, 137.0, 149.2, 152.9, 163.9 ppm; IR (KBr): n˜ =
2953, 2849, 1707, 1674, 1479, 1383, 1238, 1094, 1061, 945, 854,
1
Mp 1208C; Td 3338C; Tg 718C; H NMR (CDCl3, 400 MHz): d=1.31
(d, J=6.0 Hz, 12H), 1.93 (brs, 4H), 4.37 (brs, 4H), 4.51 (sep, J=
6.0 Hz, 2H), 7.33 ppm (s, 2H); 13C NMR (CDCl3, 100 MHz): d=22.1,
25.4, 64.6, 72.5, 118.7, 126.0, 150.5, 166.2 ppm; IR (neat): n˜ =2976,
2938, 2895, 1719, 1688, 1483, 1414, 1385, 1371, 1300, 1207, 1177,
719, 608 cmÀ1; HRMS (FAB): m/z calcd for C26H27O6: 435.1808 [M+
+
H]; found: 435.1798.
1140, 1105, 1053, 980, 955, 899, 789, 766, 746 cmÀ1
.
1
2ae: Rf =0.28 (hexane/EtOAc 10:1); mp 1638C; Td 2308C; H NMR
(CDCl3, 400 MHz): d=4.01 (s, 6H), 7.66 (s, 2H), 7.76 (d, J=0.4 Hz,
4H), 7.83 (d, J=0.4 Hz, 2H); 13C NMR (CDCl3, 100 MHz): d=56.8,
3b: To an 80 mL Schlenk flask were charged with 4 (96 mg,
0.3 mmol) and terephthaloyl chloride (5, 61 mg, 0.3 mmol). The
flask was evacuated and filled with argon. This evacuation-purge
operation was repeated twice before adding CH2Cl2 (6 mL) and 1,4-
butandiol (53 mL, 0.6 mmol). To this solution was slowly added pyri-
dine (0.19 mL, 2.4 mmol) at 08C, and the resulting solution was
stirred for 3 h at room temperature before quenching with HCl aq.
3
1
115.9 (q, JC-F =3.8 Hz), 120.0, 122.8, 122.8 (q, JC-F =271.4 Hz), 122.9,
133.1 (q, 2JC-F =34.3 Hz), 151.1, 153.2, 162.7 ppm; 19F NMR (CDCl3,
282 MHz): d=À64.9 ppm; IR (KBr): n˜ =3084, 1748, 1607, 1505,
1462, 1306, 1236, 1109, 1003, 920, 841, 731, 613 cmÀ1; HRMS (FAB):
m/z calcd for C26H15F12O6: 651.0677 [M+ +H]; found: 651.0673.
Chem. Asian J. 2018, 00, 0 – 0
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(1m). The reaction mixture was diluted with CH2Cl2 (50 mL), and
the organic layer was washed with HCl aq. (1m, 20 mL), sat.
NaHCO3 aq. (20 mL), and sat. NaCl aq. (20 mL), and dried over an-
hydrous MgSO4. The organic solvent was removed by vacuum
evaporation to give the crude product, which was dried under
vacuum and purified by GPC (eluent: CHCl3) and reprecipitation
from CH2Cl2 and MeOH, giving rise to 3b (95 mg, 56%) as colorless
solid. 3b: Mn 5160; Mw 9190; PDI 1.78 (polystyrene standard); Mp
(dec) 3328C; Tg 158C; 1H NMR (CDCl3, 400 MHz): d=1.31 (d, J=
6.0 Hz, 12H), 1.93–1.97 (m, 8H), 4.37–4.43 (m, 8H), 4.52 (sep, J=
6.0 Hz, 2H), 7.33 (s, 2H), 8.39 ppm (s, 4H); 13C NMR (CDCl3,
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150.4, 165.7, 166.2 ppm; IR (neat): n˜ =2976, 2897, 1717, 1692, 1491,
1410, 1385, 1267, 1250, 1225, 1200, 1099, 1017, 957, 874, 789,
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Acknowledgements
This work was supported by Japan Society for the Promotion
of Science (JSPS) KAKENHI (15H03795), and by the Institute of
Advanced Energy, Kyoto University (Joint Usage/Research Pro-
gram on Zero-Emission Energy Research, ZE29A-6 and ZE30A-
22).
[13] The absorption and fluorescence maxima of 2 in toluene and the
Stokes shifts are listed in Table S1.
[14] The observed fluorescence was confirmed to be prompt fluorescence
by measuring fluorescence lifetimes of 2aa in powder and in PMMA
film, which were 2.7 and 7.1 ns, respectively.
Conflict of interest
[15] CCDC 1570807 (2ac) and 1570802 (2bd) contain the supplementary
crystallographic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre.
The authors declare no conflict of interest.
[16] Gaussian 09 (Revision D.01), M. J. Frisch, G. W. Trucks, H. B. Schlegel,
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Keywords: arenes · conjugation · donor-acceptor systems ·
fluorescence · materials science
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Manuscript received: November 2, 2018
Revised manuscript received: December 11, 2018
Accepted manuscript online: December 12, 2018
Version of record online: && &&, 0000
Chem. Asian J. 2018, 00, 0 – 0
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ꢀ 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Full Paper
FULL PAPER
Masaki Shimizu,* Ryosuke Shigitani,
Takumi Kinoshita, Hiroshi Sakaguchi
&& – &&
(Poly)terephthalates with Efficient
Blue Emission in the Solid State
To di for: The disubstitution of isopro-
poxy groups at 2- and 5-positions of
terephthalic acid diesters leads to the
creation of efficient blue fluorescent or-
ganic solids. The copolymerization of
2,5-diisopropoxyterephthaloyl chloride
with butane-1,4-diol produces an effi-
cient blue fluorescent polyester film,
and the doping of a yellow-fluorescent
terephthalate into the polyester film
allows us to achieve efficient white
emission.
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Chem. Asian J. 2018, 00, 0 – 0
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10
ꢀ 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!