Twisting strategy applied to N,N-diorganoquinacridones leads to organic chromophores exhibiting efficient solid-state fluorescence

Article abstract of DOI:10.1016/j.tetlet.2011.05.087

A new molecular design of organic emitters exhibiting efficient solid-state fluorescence, which involves planarity breaking of N,N-diorganoquinacridones, is presented. The new design principle led to the development of dimethyl 2,5-diaminoterephthalates and 2,5-diamino-1,4-diaroylbenzenes, which emitted green to yellow and yellow to red light with high-to-excellent quantum yields, respectively. In addition, the photoluminescence properties of the diaroylbenzenes were dependent on the morphology and reversibly variable by thermal and solvent vapor stimuli.

Full text of DOI:10.1016/j.tetlet.2011.05.087

Tetrahedron Letters 52 (2011) 4084–4089
Contents lists available at ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Twisting strategy applied to N,N-diorganoquinacridones leads to organic
chromophores exhibiting efficient solid-state fluorescence
⇑
Masaki Shimizu , Yuiga Asai, Youhei Takeda, Akinori Yamatani, Tamejiro Hiyama
Department of Material Chemistry, Graduate School of Engineering, Kyoto University, Kyoto University Katsura, Nishikyo-ku, Kyoto 615-8510, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
A new molecular design of organic emitters exhibiting efficient solid-state fluorescence, which involves
planarity breaking of N,N-diorganoquinacridones, is presented. The new design principle led to the devel-
opment of dimethyl 2,5-diaminoterephthalates and 2,5-diamino-1,4-diaroylbenzenes, which emitted
green to yellow and yellow to red light with high-to-excellent quantum yields, respectively. In addition,
the photoluminescence properties of the diaroylbenzenes were dependent on the morphology and
reversibly variable by thermal and solvent vapor stimuli.
Received 20 April 2011
Revised 16 May 2011
Accepted 18 May 2011
Available online 25 May 2011
Keywords:
Ó 2011 Elsevier Ltd. All rights reserved.
Charge transfer
Diaroylbenzenes
Fluorescence
Solid-state emission
Terephthalates
Organic chromophores that exhibit fluorescence in the visible
region with high efficiency in the solid-state have attracted
increasing attention in the field of functional materials. This is
because the highly efficient solid-state emissions of organic fluoro-
phores are essential for the advances needed to realize optoelec-
tronic devices, such as organic light-emitting diodes (OLEDs),1
light-emitting field-effect transistors,2 semiconductor lasers,3 and
fluorescent solid sensors.4 However, most organic fluorophores
are nonluminescent or only faintly emissive in the solid-state
due to concentration quenching induced by molecular aggregation,
which is an inherent characteristic of organic solids. Hence, the
molecular design and development of organic fluorophores exhib-
iting highly efficient solid-state emissions have met limited suc-
cess,5 but such fluorophores are of great importance with respect
to both practical applications in optoelectronic devices and funda-
mental studies in solid-state molecular engineering. The reported
molecular designs that render fluorophores efficiently luminescent
in the solid-state involves (1) the incorporation of a spiro frame-
work; (2) the introduction of bulky substituents; (3) vicinal
disubstitution of aryl/aryl or alkenyl/aryl groups on an aromatic
ring or alkenyl moiety, and (4) the installation of electron-donating
and -withdrawing groups at the molecular ends and/or middles.5a
Recently, self-assembly-induced and exciplex-mediated emission
enhancement of organic gels is also demonstrated.5b–e
In this communication, we present a new guiding principle for
the design of organic fluorophores that emit visible light in the so-
lid-state with high efficiency; this principle involves double dis-
connection of N,N-diorganoquinacridones, which show intense
green fluorescence in solution but undergo severe luminescence
quenching in the solid-state (Scheme 1). The approach allows the
development of dimethyl 2,5-bis(diorganoamino)terephthalates 1
and 1,4-diaroyl-2,5-bis(diorganoamino)benzenes 2, which exhibit
efficient solid-state fluorescence in the green to yellow and yellow
to red spectral regions, respectively. The high efficiency of the
solid-state emissions is attributed to the nonplanar molecular
frameworks and the intramolecular charge-transfer (CT) character
of the S1 states. Moreover, it is notable that 2 are fluorescent
although benzophenone and its derivatives are generally nonfluo-
rescent due to rapid intersystem crossing (ISC) from the S1 state to
the T1 state.
Organic chromophores that consist of planar and rigid p-conju-
gated systems generally exhibit luminescence with high efficiency
in solution, where the chromophores are sufficiently isolated for
them not to interact electronically with one another. The planarity
of the molecular framework enhances
p-conjugation, and the
rigidity of the skeleton is beneficial in the restriction of both the
stretching and twisting motions of each bond, which can result
in radiationless deactivation of the excited states. However,
planar polycyclic chromophores normally show a strong tendency
to aggregate in the solid-state, with a
p–p stacked geometry
⇑
Corresponding author. Tel.: +81 75 383 2444; fax: +81 75 383 2445.
that causes severe luminescence quenching. Typical examples
are N,N-diorganoquinacridones, which exhibit intense green-
emissions in dilute solution, but are non or weakly-emissive in
E-mail address: m.shimizu@hs2.ecs.kyoto-u.ac.jp (M. Shimizu).
Present address: Research & Development Initiative, Chuo University, 1-13-27,
Kasuga, Bunkyo-ku, Tokyo 112-8551, Japan.
0040-4039/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2011.05.087

M. Shimizu et al. / Tetrahedron Letters 52 (2011) 4084–4089
4085
Scheme 1. Molecular design of highly emissive organic solids on the basis of planarity breaking of N,N-diorganoquinacridones.
the solid-state and even in concentrated solution.6 For example,
the photoluminescence quantum yields of N,N-dibutyl-2,9-diflu-
oroquinacridone were reportedly 0.97 in THF (1.0 Â 10À6 M) and
0.0019 in the microcrystals.6a They are, therefore, used as dopants
in OLED devices.7
solution.9 As shown in Figure 1, the phenyl and methyl groups of
the amino moiety as well as the methoxy groups are positioned
largely out of the central benzene plane (C2–C3–N1–C4 = 50.28°;
C3–C2–C1–O1 = 40.45°) and the distances between the centroids
of the central benzene rings in two adjacent molecules in the
crystal lattice are over 6 Å; there is no intermolecular aromatic
We have recently demonstrated that 1,4-bis(alkenyl)-2,5-
dipiperidinobenzenes are highly emissive fluorophores in the so-
lid-state.8 Through an investigation of their structural characteris-
tics and photophysical properties, we concluded that breaking the
high planarity of N,N-diorganoquinacridones by disconnection of
the bonds linked to the outer benzene rings, while retaining the
electronic structure consisting of a 1,4-diamino-2,5-dicarbonyl
functionality on the central benzene core, would provide new
chromophores exhibiting highly efficient visible-light fluorescence
in the solid-state if the two sets of ortho-linkages of the diorganoa-
mino and carbonyl groups could induce a twisted conformation
suitable for suppression of dense stacking in the ground state
and a large Stokes shift leading to inhibition of Förster-type energy
transfer from the excited state.
Based on this idea, there are two options for the disconnec-
tion (Scheme 1); one is cleavage of the C–CO bonds (indicated
by dotted blue lines (a), and the other involves fission of the
C–N bonds (indicated by wavy red lines (b). We initially de-
signed dimethyl 2,5-bis(arylamino)terephthalates 1 as disconnec-
tion a, and prepared them in good to high yields from dimethyl
2,5-dibromoterephthalate and anilines by Pd-catalyzed amina-
tion or commercially available dimethyl 2,5-dioxocyclohexane-
1,4-dicarboxylate via three steps (see the Supplementary data
for details).9
interaction like
molecular and crystal structures of 1d also show similar distorted
molecular conformations and the absence of
stacking.9
p–p stacking to cause emission quenching. The
p–p
Absorption and fluorescence spectra of 1d in toluene are shown
in Figure 2 as representative examples.9 The absorption maxima
appeared at 343 nm (e = 16800) and 415 nm (e = 4300), and green
fluorescence was observed with an emission maximum at 547 nm
and a quantum yield of 0.40. Thus, there was no overlap of the
absorption and fluorescence spectra, suggesting that photo-excita-
tion induced the large structural change in 1d. When a solvent was
changed from toluene to dichloromethane, the fluorescence spec-
tra red-shifted (kem = 564 nm, /f = 0.11) as shown in Figure 2.9
The HOMO, LUMO, and LUMO+1 of 1d obtained by density func-
tional theory (DFT) calculations at the B3LYP/6-31G(d) level are de-
picted in Figure 3.10 The HOMO is developed over the Ph2N–
benzene–NPh2 framework, while the MeO2C–benzene–CO2Me unit
contributes to the LUMO. Time-dependent DFT calculations reveal
that the lowest energy transition is governed mainly by the
HOMO–LUMO transition.11 Thus, the absorption band at 415 nm
can be ascribed to an intramolecular CT transition, which is consis-
tent with the large Stokes shift and the solvatochromism.
The photoluminescence properties of 1 in the crystalline and
powder states are summarized in Table 1, together with those in
toluene (the spectra are shown in Supplementary data). Upon
photo-irradiation, solid 1 exhibited intense solid-state fluorescence
Single crystals of 1b suitable for X-ray diffraction analysis were
obtained by recrystallization from dichloromethane/hexane

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M. Shimizu et al. / Tetrahedron Letters 52 (2011) 4084–4089
maxima in the crystalline and powder states for each compound. In
all cases, /f values in solution were much lower than those in the
solid-state; 1 were found to exhibit aggregation-induced emission
(AIE).12 The serious nonradiative decay in solution is presumably
attributable to the intramolecular free motion of the amino and
methoxycarbonyl moieties. Diethyl bis(4-trifluoromethylphenyl-
amino)terephthalate and diethyl bis[3,5-bis(trifluoromethyl)phe-
nylamino]terephthalate are reported to display unique thermal
stimuli-induced switching of solid-state fluorescence.13 Since the
quantum yields of the ArNH-substituted terephthalates in the
solid-state ranged from 0.066 to 0.410, it is apparent that the pres-
ence of the second carbonaceous substituents on the nitrogens of 1
is essential for attaining high solid-state quantum yields in molec-
ular design based on 2,5-diaminoterephthalate frameworks.14
Diaminodiaroylbenzenes 2, designed as disconnection
b
(Scheme 1), were synthesized as colored solids from 2,5-dibro-
moterephthaloyl dichloride via three steps (Figure 5a–h, the upper
photographs).9 During purification and isolation, we observed that
the colors of the isolated solids 2b and 2e were very sensitive to
the preparative history of each solid sample. Recrystallization of
2b from THF/MeOH solution and slow evaporation (220 hPa,
40 °C) of a THF solution gave yellow microcrystals and powder
(Fig. 5c,d), respectively; quick evaporation (60 hPa, 40 °C) afforded
a red powder (Fig. 5e). DSC analysis of 2b in red powder showed an
exothermic phase-transition peak at 127 °C.9 When the red powder
was heated at 130 °C, it changed color to yellow. Recrystallization
of 2e from THF/MeOH solution provided red microcrystals (Fig. 5f),
and quick evaporation of a THF solution left a mixture of orange
and red powders. Interestingly, all of the red powder in the mixture
turned orange (Fig. 5g) upon heating the mixture at 100 °C.9 In
turn, the resulting orange powder gradually and completely turned
red (Fig. 5h) when the powder was exposed to dichloromethane
vapor for 24 h.15 The color-changing process was found to be
reversible. These observations indicate that the photophysical
properties of 2b and 2e in the solid-state are very sensitive to sub-
tle differences in morphology.
With this morphology-sensitive behavior of 2 in mind, we
measured the photoluminescence of the crystals and powders.
The results are summarized in Table 2, along with the results ob-
tained from measurements in toluene. All of the prepared solid
samples emitted brilliantly visible light ranging from yellow to
deep red (Fig. 5a–h, the lower photographs). Comparison of the
solid-state emissions with those in solution confirms that 2 are
also AIE-active chromophores. There was no overlap of the
absorption and emission spectra of 2; in other words, large Stokes
shifts were observed, as illustrated by the example of 2b in Figure
6. Changing a solvent from toluene to dichloromethane induced a
Figure 1. Molecular and crystal structures of 1b: space group P-1 (triclinic),
a = 6.0995(13), b = 8.5112(19), c = 11.134(2),
= 107.081(4)°. Hydrogens are omitted for clarity. (a) top view, (b) side view, (c)
packing view from a axis, and (d) packing view from c axis.
a = 95.713(4)°, b = 104.354(4)°,
c
Table 1
Photoluminescence data of 1
kem (nm) (/f)b
a
Entry
1
Microcrystalsc
Powderd
Solutione
1
2
3
4
5
6
7
1a
1b
1c
1d
1e
1f
523 (0.47)
539 (0.64)
553 (0.47)
519 (0.44)
572 (0.67)
571 (0.60)
504 (0.76)
527 (0.32)
544 (0.60)
549 (0.43)
516 (0.71)
565 (0.76)
568 (0.63)
508 (0.72)
514 (0.15)
544 (0.03)
—
f
547 (0.40)
556 (0.18)
f
—
1g
499 (0.54)
Figure 2. Absorption and fluorescence spectra of 1d.
a
Emission maxima upon photo-irradiation (kex = 400 nm).
b
Absolute quantum yield determined with
a calibrated integrating sphere
system.
ranging from green to yellow, with good to high quantum yields
(/f = 0.32–0.76). The fluorescence spectra of solid 1d are shown
in Figure 2.9 Some photographs of the irradiated samples are
shown in Figure 4. There is no big difference between the emission
c
Prepared by recrystallization from dichloromethane/hexane.
Prepared by evaporation (600 hPa, 40 °C) of CH2Cl2 solution.
1 Â 10À5 M in toluene.
d
e
f
No fluorescence was observed.

M. Shimizu et al. / Tetrahedron Letters 52 (2011) 4084–4089
4087
Figure 3. HOMO (a), LUMO (b), and LUMO+1 (c) diagrams of 1d.
red-shift of the fluorescence spectra as observed with 1 (see the
Supplementary data for details).9 X-ray single crystal analysis of
2a revealed that the piperidyl and benzoyl groups were largely
out of the central benzene plane.9 DFT calculations indicate that
the photoluminescence is also governed by intramolecular CT
transitions (Fig. 7).10 The emissions appeared in a longer wave-
length region than those of 1; this can be ascribed to the en-
hanced intramolecular CT character of the transitions as a result
of the stronger electron-withdrawing effects of aroyl moieties
compared with those of methoxycarbonyl groups. Since red-emis-
sive organic fluorophores in the neat solid-state generally have a
strong tendency to cause aggregation, which results in severe
concentration quenching, it is a formidable challenge to attain
quantum yields exceeding 0.3 with regard to red emissions from
neat organic solids.16 It is, therefore, noteworthy that 2d and 2e
in crystals exhibit red emission at 640 and 650 nm with excellent
quantum yields of 0.33 and 0.47, respectively.
5.9 ns;
s
2a, powder) = 8.1 ns;
s
2b, crystal) = 22.5 ns;
s
2b,
powder) = 10.3 ns and 4.7 ns.17 Generally, diaryl ketones in which
the orbital configuration of the S1 state is assigned to n–p⁄ transi-
tions of the ketone carbonyl group are almost nonfluorescent
(/f = ꢀ0.01–0.0001) because ISC from the S1 state to the T1 state
is much faster than the relatively slow radiative decay.18 For exam-
ple, benzophenone exhibits no fluorescence in solution at room
temperature and shows phosphorescence at low temperatures in
a frozen solvent due to highly efficient ISC (/ISC = 1.0).19 Room-
temperature phosphorescence from crystals of benzophenone
and its derivatives have also been demonstrated very recently.20
Compared with these features of phosphorescence emissions from
diaryl ketones, the observed efficient fluorescence from 2, which
possesses two diaryl ketone moieties, clearly implies that the
intramolecular CT transitions induced by the amino groups substi-
tuted at the ortho-positions mainly govern the electronic structure
of the S1 state in favor of the n–p⁄ transitions of the ketone carbon-
yls. This is consistent with nearly no distribution of the HOMO on
the carbonyl oxygen and significant contribution of the amino
groups to the HOMO (Fig. 7).
It should be noted that the luminescence from 2 originates in
radiative decay of the S1 state, that is, fluorescence; this is con-
firmed by lifetime measurements;
s 2a, crystal) = 15.2 ns and
Figure 4. Photoluminescence images of 1: (a) crystals of 1b, (b) crystals of 1d, (c) powder of 1d, and (d) powder of 1e.
Figure 5. Optical and fluorescence images of 2: (a) crystals of 2a, (b) powder of 2a; (c) crystals of 2b; (d) yellow powder of 2b; (e) red powder of 2b; (f) crystals of 2e; (g)
orange powder of 2e; and (h) red powder of 2e under natural light (the upper photograph of each entry) and a UV lamp (the lower photograph of each entry).

4088
M. Shimizu et al. / Tetrahedron Letters 52 (2011) 4084–4089
Table 2
quantum yield of solid-state red fluorescence is attained with
Photoluminescence data of 2a
1,4-dibenzoyl-2,5-bis(4-methylphenyl)benzene (/f = 0.47 with an
emission maximum of 650 nm). The molecular design of these
new solid fluorophores originates in the idea of planarity breaking
of N,N-diorganoquinacridones, and the success of the design is now
prompting us to apply this molecular design concept to other types
of planar dopant emitters, such as coumarins, in order to extend
the validity of the design principle. Furthermore, we have found
b
c
Entry
2
Color and shape
kem (nm)
/
f
1
2
3
4
5
6
7
8
2a
Orange crystalsd
Orange powdere
(In toluene)f
608
588
0.38
0.14
g
g
—
—
2b
Yellow crystalsd
Yellow powderh
Red powdere
(In toluene)f
562
565
637
602
614
610
603
640
640
633
650
610
657
623
0.61
0.35
0.22
0.20
0.60
0.44
0.23
0.33
0.18
0.14
0.47
0.30
0.20
0.16
that 1,4-diaroyl-2,5-bis(diorganoamino)benzenes constitute
a
2c
2d
2e
Orange crystalsd
Orange powdere
(In toluene)f
new class of polymorphic solids that exhibit morphology-sensitive
luminescence. These findings make 2,5-bis(diorganoamino)-1,4-
diaroylbenzenes potentially attractive as organic emitting materi-
als, not only for OLEDs, but also for sensing and switching devices
that utilize solid-state luminescence as an output.22 Further stud-
ies on these polymorphic structures and their relationship with
photophysical properties are in progress.
9
10
11
12
13
14
15
16
17
Red crystalsd
Red powdere
(In toluene)f
Red crystalsd
Orange powderi
Red powderj
(In toluene)f
Acknowledgments
a
b
c
Irradiation was effected at 400 nm for 2a and 450 nm for 2b–e.
Emission maxima.
Absolute quantum yield determined with
This work was supported by Grants-in-Aid for Creative
Scientific Research, No. 16GS0209, and Scientific Research, No.
22350081, from the Ministry of Education, Culture, Sports, Science
and Technology, Japan. The authors thank Mr. Hirohiko Watanabe,
Hamamatsu Photonics K.K. for measurement of luminescence
lifetime.
a calibrated integrating sphere
system.
d
Prepared by recrystallization from THF/MeOH solution.
Prepared by evaporation (60 hPa, 40 °C) of THF solution.
2 Â 10À5 M in toluene.
e
f
g
h
i
No fluorescence was observed.
Prepared by slow evaporation (220 hPa, 40 °C) of THF solution.
Prepared by evaporation (60 hPa, 40 °C) of THF solution followed by heating at
100 °C.
Supplementary data
j
Prepared by evaporation (60 hPa, 40 °C) of THF solution followed by heating at
100 °C, and then exposure to a vapor of dichloromethane for 24 h.
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.tetlet.2011.05.087.
References and notes
1. (a)Highly Efficient OLEDs with Phosphorescent Materials; Yersin, H., Ed.; Wiley-
VCH: Weinheim, 2008; (b)Organic Light-Emitting Devices. Synthesis, Properties
and Applications; Müllen, K., Scherf, U., Eds.; Wiley-VCH: Weinheim, 2006; (c)
Friend, R. H.; Gymer, R. W.; Holmes, A. B.; Burroughes, J. H.; Marks, R. N.;
Taliani, C.; Bradley, D. D. C.; Dos Santos, D. A.; Brédas, J. L.; Lögdlund, M.;
Salaneck, W. R. Nature 1999, 397, 121–128.
2. (a) Zaumseil, J.; Sirringhaus, H. Chem. Rev. 2007, 107, 1296–1323; (b) Cicoira, F.;
Santato, C. Adv. Funct. Mater. 2007, 17, 3421–3434.
3. (a) Samuel, I. D. W.; Turnbull, G. A. Mater. Today 2004, 7, 28–35; (b) Scherf, U.;
Riechel, S.; Lemmer, U.; Mahrt, R. F. Curr. Opin. Solid State Mater. Sci. 2001, 5,
143–154; (c) McGehee, M. D.; Heeger, A. J. Adv. Mater. 2000, 12, 1655–1668; (d)
Kranzelbinder, G.; Leising, G. Rep. Prog. Phys. 2000, 63, 729–762; (e) Tessler, N.
Adv. Mater. 1999, 11, 363–370; (f) Kozlov, V. G.; Forrest, S. R. Curr. Opin. Solid
State Mater. Sci. 1999, 4, 203–208; (g) Dodabalapur, A.; Chandross, E. A.;
Berggren, M.; Slusher, R. E. Science 1997, 277, 1787–1788.
4. Reviews on fluorescent sensors: (a) Thomas, S. W.; Joly, G. D.; Swager, T. M.
Chem. Rev. 2007, 107, 1339–1386; (b) Carol, P.; Sreejith, S.; Ajayaghosh, A.
Chem. Asian J. 2007, 2, 338–348; (c) Basabe-Desmonts, L.; Reinhoudt, D. N.;
Crego-Calama, M. Chem. Soc. Rev. 2007, 36, 993–1017; (d) Wolfbeis, O. S. J.
Mater. Chem. 2005, 15, 2657–2669; (e) Callan, J. F.; De Silva, A. P.; Magri, D. C.
Tetrahedron 2005, 61, 8551–8588; (f) Martinez-Manez, R.; Sancenon, F. Chem.
Rev. 2003, 103, 4419–4476; (g) De Silva, A. P.; Gunaratne, H. Q. N.;
Gunnlaugsson, T.; Huxley, A. J. M.; McCoy, C. P.; Rademacher, J. T.; Rice, T. E.
Chem. Rev. 1997, 97, 1515–1566; Selected examples of solid-state fluorescent
sensors: (h) Esser, B.; Swager, T. M. Angew. Chem., Int. Ed. 2010, 49, 8872–8875;
Figure 6. Absorption spectra of 2b in toluene and fluorescence spectra of 2b in
toluene, as crystals, and as a powder.
In summary, we have demonstrated that dimethyl 2,5-
bis(diorganoamino)terephthalates and 1,4-diaroyl-2,5-bis(diorg-
anoamino)benzenes in the solid-state exhibit intense green to yel-
low and yellow to red fluorescence, respectively, with good to high
quantum yields.21 In particular, it is remarkable that an excellent
Figure 7. HOMO (a) and LUMO (b) diagrams of 2a.

M. Shimizu et al. / Tetrahedron Letters 52 (2011) 4084–4089
4089
(i) Sreejith, S.; Divya, K. P.; Ajayaghosh, A. Chem. Commun. 2008, 2903–2905; (j)
Dale, T. J.; Rebek, J. J. Am. Chem. Soc. 2006, 128, 4500–4501; (k) Zhang, S. W.;
Swager, T. M. J. Am. Chem. Soc. 2003, 125, 3420–3421; (l) Yang, J. S.; Swager, T.
M. J. Am. Chem. Soc. 1998, 120, 11864–11873; (m) Yang, J. S.; Swager, T. M. J.
Am. Chem. Soc. 1998, 120, 5321–5322.
12. (a) Luo, J.; Xie, Z.; Lam, J. W. Y.; Cheng, L.; Chen, H.; Qiu, C.; Hoi Sing, K.; Zhan,
X.; Liu, Y.; Zhu, D.; Tang, B. Z. Chem. Commun. 2001, 1740–1741; (b) Hong, Y.;
Lam, J. W. Y.; Tang, B. Z. Chem. Commun. 2009, 4332–4353; (c) Liu, J.; Lam, J. W.
Y.; Tang, B. Z. J. Inorg. Organomet. Polym. Mater. 2009, 19, 249–285. and
references cited therein.
5. Review on small organic molecules exhibiting highly efficient solid-state
fluorescence: (a) Shimizu, M.; Hiyama, T. Chem. Asian J. 2010, 5, 1516–1531;
Design and development of efficiently luminescent organic gels: (b) Babu, S. S.;
Kartha, K. K.; Ajayaghosh, A. J. Phys. Chem. Lett. 2010, 1, 3413–3424; (c) Babu, S.
S.; Praveen, V. K.; Prasanthkumar, S.; Ajayaghosh, A. Chem. Eur. J. 2008, 14,
9577–9584; (d) Ajayaghosh, A.; Praveen, V. K.; Srinivasan, S.; Varghese, R. Adv.
Mater. 2007, 19, 411–415; (e) An, B.-K.; Lee, D.-S.; Lee, J.-S.; Park, Y.-S.; Song, H.-
S.; Park, S. Y. J. Am. Chem. Soc. 2004, 126, 10232–10233.
6. (a) Zhao, Y.; Mu, X.; Bao, C.; Fan, Y.; Zhang, J.; Wang, Y. Langmuir 2009, 25,
3264–3270; (b) Fan, Y.; Zhao, Y.; Ye, L.; Li, B.; Yang, G.; Wang, Y. Cryst. Growth
Des. 2009, 9, 1421–1430; (c) Wang, J.; Zhao, Y.; Zhang, J.; Yang, B.; Wang, Y.;
Zhang, D.; You, H.; Ma, D. J. Phys. Chem. C 2007, 111, 9177–9183; (d) Mizuguchi,
J.; Senju, T. J. Phys. Chem. B 2006, 110, 19154–19161; (e) Ye, K.; Wang, J.; Sun,
H.; Liu, Y.; Mu, Z.; Li, F.; Jiang, S.; Zhang, J.; Zhang, H.; Wang, Y.; Che, C. M. J.
Phys. Chem. B 2005, 109, 8008–8016.
7. N,N-Diphenylquinacridone: (a) Shi, J.; Tang, C. W. Appl. Phys. Lett. 1997, 70,
1665–1667; N,N-Dibutylquinacridone: (b) Murata, H.; Merritt, C. D.; Inada, H.;
Shirota, Y.; Kafafi, Z. H. Appl. Phys. Lett. 1999, 75, 3252–3254. N,N-
Diethylquinacridone:; (c) Ref. [6e].; N,N-Dimethylquinacridone: (d)
Dobbertin, T.; Werner, O.; Meyer, J.; Kammoun, A.; Schneider, D.; Riedl, T.;
Becker, E.; Johannes, H. H.; Kowalsky, W. Appl. Phys. Lett. 2003, 83, 5071–5073.
8. Shimizu, M.; Takeda, Y.; Higashi, M.; Hiyama, T. Angew. Chem., Int. Ed. 2009, 48,
3653–3656.
9. Supplementary data includes preparation, characterization data, and data on
photophysical properties of 1 and 2. Crystallographic data for 1b, 1d, and 2a
(CCDC–801000, –801001, and –801002), and DSC charts of 2b and 2e in
powder are also shown in Supplementary data. Although compound 1d was
reportedly prepared as an intermediate in the preparation of
poly[(diaminophenylene)vinylene]s, no photophysical properties and crystal
structure of 1d were examined Shi, J.; Zheng, S. Macromolecules 2001, 34, 6571–
6576.
13. Zhao, Y.; Gao, H.; Fan, Y.; Zhou, T.; Su, Z.; Liu, Y.; Wang, Y. Adv. Mater. 2009, 21,
3165–3169.
14. Fluorescence quantum yields of 2,5-bis(arylamino)terephthalates in solution
were reportedly to range from 0.013 to 0.23 Zhang, Y.; Starynowicz, P.;
Christoffers, J. Eur. J. Org. Chem. 2008, 3488–3495.
15. We confirmed that no detectable dichloromethane was present in the red
powder of 2e by 1H NMR, indicating that the color change from orange to red
did not result from the formation of inclusion/co-ordination complexes of 2e
and dichloromethane. Examples of solvent vapor-induced color/luminescence
change of chromophores in the solid-state: (a) Ooyama, Y.; Kagawa, Y.;
Fukuoka, H.; Ito, G.; Harima, Y. Eur. J. Org. Chem. 2009, 5321–5326; (b) Dong, Y.;
Lam, J. W. Y.; Qin, A.; Li, Z.; Sun, J.; Sung, H. H. Y.; Williams, I. D.; Tang, B. Z.
Chem. Commun. 2007, 40–42; (c) Fukushima, T.; Takachi, K.; Tsuchihara, K.
Macromolecules 2006, 39, 3103–3105; (d) Ohshita, J.; Lee, K. H.; Hashimoto, M.;
Kunugi, Y.; Harima, Y.; Yamashita, K.; Kunai, A. Org. Lett. 2002, 4, 1891–1894;
(e) Rakow, N. A.; Suslick, K. S. Nature 2000, 406, 710–713.
16. (a) Chen, C. T. Chem. Mater. 2004, 16, 4389–4400; (b) Ref. [5].; (c) Wakamiya,
A.; Mori, K.; Yamaguchi, S. Angew. Chem., Int. Ed. 2007, 46, 4273–4276; (d)
Matsui, M.; Ikeda, R.; Kubota, Y.; Funabiki, K. Tetrahedron Lett. 2009, 50, 5047–
5049.
17. Lifetimes of photoluminescence were measured with Quantaurus-Tau
(Hamamatsu Photonics K.K.).
18. Turro, N. J. Modern Molecular Photochemistry; University Science Books:
Sausalito, 1978. chapter 5.
19. Lamola, A. A.; Hammond, G. S. J. Chem. Phys. 1965, 43, 2129–2135.
20. Yuan, W. Z.; Shen, X. Y.; Zhao, H.; Lam, J. W. Y.; Tang, L.; Lu, P.; Wang, C.; Liu, Y.;
Wang, Z.; Zheng, Q.; Sun, J. Z.; Ma, Y.; Tang, B. Z. J. Phys. Chem. C 2010, 114,
6090–6099.
21. We preliminarily confirmed that UV irradiation of 1b, 1d, 2a, and 2b in the
solid-state with a 400 W high-pressure mercury lamp at room temperature for
6 h resulted in no change of the fluorescence spectra and quantum yields.
22. (a) Mutai, T.; Tomoda, H.; Ohkawa, T.; Yabe, Y.; Araki, K. Angew. Chem.,
Int. Ed. 2008, 47, 9522–9524; (b) Quartapelle Procopio, E.; Mauro, M.;
Panigati, M.; Donghi, D.; Mercandelli, P.; Sironi, A.; D’Alfonso, G.; De Cola,
L. J. Am. Chem. Soc. 2010, 132, 14397–14399; (c) Anthony, S. P.; Draper, S.
M. J. Phys. Chem. C 2010, 114, 11708–11716; (d) Sagara, Y.; Kato, T. Nature
Chem. 2009, 1, 605–610.
10. DFT calculations of 1d and 2a at the B3LYP/6-31G(d) level were carried out
using the crystal structures by the Gaussian 03 package (Revision E.01, M. J.
Frisch et al., Gaussian, Inc., Wallingford CT, 2004). For details, see
Supplementary data.
11. The higher transition can be assigned to the HOMO–LUMO+1 transition (
transition).
p–
p⁄