New indole-containing luminophores: Convenient synthesis and aggregation- induced emission enhancement

Article abstract of DOI:10.1002/poc.1461

A series of new indole-based luminophores (lla-d) were conveniently synthesized through Ullmann reactions. They were well characterized by spectroscopic analyses and exhibited aggregation-induced emission enhancement (AIEE) properties. By simply changing

Full text of DOI:10.1002/poc.1461

Research Article
Received: 2 August 2008,
Revised: 15 September 2008,
Accepted: 20 September 2008,
Published online in Wiley InterScience: 12 November 2008
(www.interscience.wiley.com) DOI 10.1002/poc.1461
New indole-containing luminophores:
convenient synthesis and aggregation-
induced emission enhancement
a
a
a
a
*
Qianqian Li , Shanshan Yu , Zhen Li and Jingui Qin
A series of new indole-based luminophores (IIa–d) were conveniently synthesized through Ullmann reactions. They
were well characterized by spectroscopic analyses and exhibited aggregation-induced emission enhancement (AIEE)
properties. By simply changing the aromatic moieties in IIa–d, their maximum emission wavelengths could be well-
tuned from 340 to 400 nm. The obtained experimental results, including the fluorescent behavior and the crystal
structure in solid, demonstrated that the AIEE phenomena are caused by the restrictions of the intramolecular indolyl
vibrational and rotational motions (around the Carbon–Nitrogen bonds). Copyright ß 2008 John Wiley & Sons, Ltd.
Supporting information may be found in the online version of this article.
Keywords: indole; aggregation-induced emission enhancement; carbon–nitrogen bonds
designed and demonstrated AIE properties.[51,52] As seen in
INTRODUCTION
Chart 1, in the AIE molecules, different p-construction blocks are
linked together only through Carbon–Carbon bonds. The question
can be posed: could other different linkage modes yield more AIE
or AIEE molecules? If other linkage modes were possible, the
family of molecules displaying AIE and AIEE will be expanded to a
large degree.
Organic luminophores have attracted increasing interest due to
their potential applications as biological probes, chemical
sensors, and organic light-emitting diodes, in the past decades.
Thanks to the extensive efforts by many researchers, many kinds
of luminophores with desirable properties have been devel-
oped.[1–15] However, to realize their practical utilization more
comprehensively, some issues should be addressed. For example,
organic luminophores generally exhibit strong luminescence in
dilute solutions, however, in the solid state or in solutions with
high concentration, the formation of delocalized excitons or
excimers, due to the aggregation of the luminophores, often
quenches their emission.[16–22] Thus, much effort has been
applied to suppress the aggregation of organic lumino-
phores.[23,24] In contrast to the normal thought of hampering
the aggregation of luminophores, the best approach to the above
notorious problem might be to develop new luminophoric
materials whose aggregates could emit more efficiently than
their solutions.[25–28] Along this line of approach, two novel
photoluminescence (PL) processes have been identified: one is
the ‘aggregation-induced emission enhancement (AIEE)’ and
another is the ‘aggregation-induced emission (AIE)’.[29–46] Siloles
(TPS, Chart 1) are typical examples of AIE molecules, which were
non-emissive in dilute solutions but highly emissive upon
aggregation with the fluorescent quantum yields two orders
of magnitude higher. As to the possible mechanism, the
theoretical calculations, the experimental results obtained by a
time-resolved fluorescence technique, and the internal structural
control of silole examples, strongly supported the hypothesis that
the AIE phenomena were due to the restrictions of the
intramolecular phenyl vibrational and rotational motions (around
the Carbon–Carbon bonds).[47–50] According to this point, some
new AIE molecules were developed. For example, tetrapheny-
lethene (TPE, Chart 1) and 4-n-butoxybiphenyl (BBP) were
In recent years, a series of AIE active molecules have been
utilized as good bioprobes for protein, DNA, and even the
formation of G-Quadruplex,[53–55] demonstrating the huge
practical application of AIE (or AIEE) molecules in the field of
biology. It is also envisaged that the AIE (or AIEE) molecules could
be applied to detect some special biomacromolecules in live cell
and perhaps, live organism selectively and sensitively. To realize
this point, the AIE (or AIEE) molecules should be biocompatible, in
addition to their good AIE (or AIEE) properties. Recently, we were
interested in one heterocyclic moiety, indole, which is a very
important constructing block in many naturally occurring
compounds, and plays an important role in the fields of
biochemistry and medicine (Chart 2). For example, indomethacin,
the methylated indole derivative, is a non-steroidal anti-
inflammatory drug commonly used to reduce fever, pain,
stiffness, and swelling; indole-3-acetic acid, also known as IAA,
is a member of the group of phytohormones called auxins, and is
generally considered to be the most important native auxin; and
L-tryptophan, an indole-containing amino acid, is used to
*
Correspondence to: Z. Li, Department of Chemistry, Hubei Key Lab on Organic
and Polymeric Opto-Electronic Materials, Wuhan University, Wuhan 430072,
China.
E-mail: lizhen@whu.edu.cn
a
Q. Li, S. Yu, Z. Li, J. Qin
Department of Chemistry, Hubei Key Lab on Organic and Polymeric Opto-
Electronic Materials, Wuhan University, Wuhan 430072, China
J. Phys. Org. Chem. 2009, 22 241–246
Copyright ß 2008 John Wiley & Sons, Ltd.

Q. LI ET AL.
EXPERIMENTAL SECTION
Materials and instrumentation
9-n-Hexyl-3,6-diiodocarbazole (Ib), 9,9-di-n-hexyl-2,7-diiodofluo-
rene(Ic), and 4-(n-hexyloxy)-N,N-bis(4-iodophenyl)aniline(Id) were
synthesized according to the literature methods. All other reagents
wereusedasreceived. 1Hand13CNMRspectraweremeasuredona
Varian Mercury300 spectrometer using tetramethylsilane (TMS;
d ¼ 0 ppm) as internal standard. The Fourier transform infrared
(FTIR) spectra were recorded on a PerkinElmer-2 spectrometer in
the region of 3000–4000 cmꢀ1. UV–Visible spectra were obtained
using a Schimadzu UV-2550 spectrometer. EI-MS spectra were
recorded with a Finnigan PRACE mass spectrometer. Thermal
analysiswasperformedonNETZSCHSTA449Cthermalanalyzerata
heating rate of 10 8C minꢀ1 in argon at a flow rate of 30cm3 minꢀ1
for thermogravimetric analysis (TGA). Elemental analyses were
performed by a CARLOERBA-1106 micro-elemental analyzer. The
thermometer for measurement of the melting point was
uncorrected. Photoluminescence spectra were obtained on a
Hitachi F-4500 fluorescence spectrophotometer. Single-crystal
X-ray diffraction data were collected on a Bruker SMART
diffractometer with an Apex CCD detector diffractometer using
graphite-monochromatic Mo-Ka radiation at 293 K.
Chart 1.
Chart 2.
Synthesis of compound IIa
A mixture of indole (1.17 g, 10.0 mmol), 1,4-diiodobenzene (1.65 g,
5.00 mmol), copper powder (1.92g, 30.0 mmol), potassium carbon-
ate(6.90 g, 50.0 mmol), and 18-crown-6(39.6 mg, 0.15mmol)in1,2-
dichlorobenzene (20 ml) was heated at 180 8C for 48 h under an
atmosphere of argon. After cooled to room temperature, the
inorganic components were removed by filtration. The solvent was
distilled under reduced pressure and the crude product was
purified with column chromatography on silica gel using
petroleum/ethyl acetate (20/1) as eluent to afford a white powder
(500 mg, 32%). (Found:C,85.01;H,5.54;N,8.75.C22H16N2 requiresC,
85.69;H, 5.23;N, 9.08%);1HNMR(300 MHz;CDCl3; TMS)7.73(2H, d,J
7.5, ArH), 7.65(6H, d, J 8.4, ArH), 7.41(2H, d, J 2.7, ArH), 7.31–7.22(4H,
m, ArH), 6.75 (2H, d, J 3.0, ArH); 13C NMR (300MHz; CDCl3; TMS):
138.2, 136.1, 129.6, 128.1, 125.6, 122.9, 121.5, 120.8, 110.7, 104.3;mp
217–2198C; m/z (EI) 307.2 (Mþꢀ1. C22H16N2 requires 308.1).
alleviate depression, support alcohol withdrawal, and to aid
weight loss. Thus, indole moieties should be biocompatible to live
cells and the human body.[56–62] Considering this point, we
wondered if it was possible to design some indole-based AIE
active luminophores.
As mentioned above, the AIE (or AIEE) phenomena were
derived from the restrictions of the intramolecular phenyl
vibrational and rotational motions (around the Carbon–Carbon
bonds). Accordingly and partially based on our previous work on
indole moieties,[63–67] we would like to introduce some aromatic
rings to indole groups through Carbon–Nitrogen bonds (the
structure shown in Chart 2), and explore if it is possible to obtain
new indole-based AIE (or AIEE) active molecules. Therefore, as
shown in Scheme 1, four new indole-based compounds were
prepared conveniently through the copper-catalyzed Ullmann
amination reaction. The experimental results demonstrated that
they were AIEE active luminophores, confirming that the linkage
mode of Carbon–Nitrogen bonds could also work for the design
of new AIE (or AIEE) active molecules. By changing the introduced
aromatic moieties, the maximum emission wavelength of the
resultant indole-based luminophores could be adjusted. Herein,
we would like to present their syntheses, characterizations, and
optical properties in detail.
Synthesis of compound IIb
A mixture of indole (1.17 g, 10.0 mmol), 3,6-diiodocarbazole
(2.51 g, 5.00 mmol), copper powder (1.92 g, 30.0 mmol), potass-
ium carbonate (6.90 g, 50.0 mmol), and 18-crown-6 (39.6 mg,
0.15 mmol) in 1,2-dichlorobenzene (20 ml) was heated at 180 8C
for 48 h under an atmosphere of argon. After cooled to room
temperature, the inorganic components were removed by
H
N
Ar
Cu/K2CO3/18-crown-6
1,2-dichlorobenzene
Ar
I
I
+
N
N
IIa-d
Ia-d
1
C6H13
N
C6H13
C6H13
Ar
=
C6H13O
N
a
b
d
c
Scheme 1.
www.interscience.wiley.com/journal/poc
Copyright ß 2008 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2009, 22 241–246

INDOLE-CONTAINING LUMINOPHORES
filtration. The solvent was distilled under reduced pressure and
the crude product was purified with column chromatography on
silica gel using petroleum/ethyl acetate (20/1) as eluent to afford
a white powder (900 mg, 38%). (Found: C, 85.09; H, 5.95; N,
8.57. C34H31N3 requires C, 84.79; H, 6.49; N, 8.72%); 1H NMR
(300 MHz; CDCl3; TMS): 8.18 (2H, d, J 1.5, ArH), 7.73 (2H, d, J 6.6,
ArH), 7.67–7.63 (2H, m, ArH), 7.58–7.54 (4H, m, ArH), 7.43 (2H, d, J
3.6, ArH), 7.26–7.16 (4H, m, ArH), 6.72 (2H, d, J 3.6, ArH), 4.43 (2H, t,
J 7.2, N—CH2), 1.99 (2H, m, CH2), 1.49–1.32 (6H, m, CH2), 0.92 (3H,
t, J 7.5, CH3); 13C NMR (300 MHz; CDCl3; TMS):139.9, 137.0, 132.1,
129.2, 124.0, 123.3, 122.4, 121.3, 120.4, 117.4, 110.7, 109.9, 103.1,
43.8, 31.9, 29.4, 27.3, 22.9, 14.4; mp 62–64 8C; m/z (EI) 481.5
(Mþ. C34H31N3 requires 481.3).
similar procedure of Ullmann reactions reported in the
literatures.[68,69] The yields were acceptable for Ullmann reac-
tions.[70,71] It should be pointed out that the meta position to the
nitrogen atom in the indole ring is very active, many substitutions
could easily take place at this position. In IIa–d, these positions
were left intact, thus some other functional groups could be
substituted here to offer new functionality to these indole-based
AIEE active molecules. For example, some hydrophilic groups
could be introduced to enhance the solubility of the resultant
molecules in water, leading to their possible utilization in live cells
or the human body. This work is under way in our laboratory.
IIa–d were well characterized by 1H NMR, 13C NMR, FT-IR,
elemental analysis and EI-MS, and gave satisfactory data
(Experimental section and Supporting Information). They were
found to be thermally stable, with their TGA thermograms shown
in Fig. S5. The 5% weight loss temperatures of IIa, IIb, and IId
were 248, 365, and 363 8C, respectively. The good thermal
stability would benefit their potential practical application.
Synthesis of compound IIc
A mixture of indole (0.28 g, 2.40 mmol), 9,9-dihexyl-2,7-diiodo-
fluorene (0.70 g, 1.20 mmol), copper powder (0.46 g, 7.20 mmol),
potassium carbonate (1.66 g, 12.0 mmol), and 18-crown-6
(9.51 mg, 0.036 mmol) in 1,2-dichlorobenzene (5 ml) was heated
at 180 8C for 48 h under an atmosphere of argon. After cooled to
room temperature, the inorganic components were removed by
filtration. The solvent was distilled under reduced pressure and
the crude product was purified with column chromatography on
silica gel using petroleum/ethyl acetate (20/1) as eluent to afford
a colorless oil (450 mg, 67%). 1H NMR (300 MHz; CDCl3; TMS): 7.84
(2H, d, J 9.0, ArH), 7.72 (2H, d, J 7.5, ArH), 7.59 (2H, d, J 8.4, ArH),
7.50 (4H, br s, ArH), 7.43 (2H, br s, ArH), 7.25–7.19 (4H, m, ArH), 6.73
(2H, s, ArH), 2.02 (4H, br s, CH2), 1.11 (12H, br s, CH2), 0.78 (10H, br
s, CH2 and CH3); 13C NMR (300 MHz; CDCl3; TMS): 151.4, 137.8,
137.6, 134.8, 128.3, 127.1, 122.3, 121.3, 120.2, 119.6, 119.3, 118.0,
109.5, 102.5, 54.5, 39.2, 30.5, 28.6, 22.9, 21.5, 13.0; m/z (EI) 564.3
(Mþ. C41H44N2 requires 564.4).
Aggregation-induced emission enhancement (AIEE)
properties and photophysics
All the obtained indole-based luminophores were soluble in
common solvents, such as chloroform, acetone, ethanol, THF,
acetonitrile, and dichloromethane. However, they demonstrated
poor solubility in water. The UV–Vis absorption spectra are shown
in Figs. S6–S14 with different concentrations. As the aromatic
moieties between the two indolyl groups are different, IIa–d
exhibited different absorption behavior.
IIa–d emitted detectable fluorescence upon excitation in dilute
solutions. Figure 1 shows the fluorescent spectra of IIa–d in the
THF solutions. The intensity was normalized for the comparison
of their different maximum emission wavelengths. In IIa, two
indolyl moieties are linked together by one phenyl group, and the
maximum emission wavelength of this luminophore was
observed at about 340 nm;.when the phenyl group was changed
to a carbazolyl one in IIb, the wavelength was red-shifted to
360 nm. Similar phenomena were observed when fluorene and
triphenylamino moieties were used in IIc and IId, respectively,
with the maximum emission wavelengths at 392 and 400 nm,
respectively. These results indicated that there are strong
electronic interactions between the introduced aromatic rings
and the two end-capped indolyl moieties through the Carbon–
Nitrogen single bonds, to form an extended p system throughout
the whole molecule. And by changing the aromatic group used,
the maximum emission wavelength can be adjusted from
ultraviolet region to the blue region of the visible spectrum. Thus,
we can control the emission behavior of this kind of indole-based
luminophore to some degree, as required for the potential
applications, by simply introducing different aromatic moieties.
Further work is in progress in our laboratory.
To determine whether the four indole-based luminophores
were AIEE active or not, their fluorescence behavior was studied
in mixture of THF and water of varying composition, since they
could easily dissolve in THF but are insoluble in water (Figs. 2 and
S15). Since the FF values of IIa–d could not be accurately
determined due to the involved technical difficulty, we thus
plotted the changes in their PL peak intensities versus water
content of the mixture (Fig. 2B). When the water fraction was
increased from 0 to 50%, the fluorescence intensity of IId was
enhanced correspondingly. This increase in fluorescence inten-
sity can be attributed to an AIEE effect caused by the formation of
Synthesis of compound IId
A mixture of indole (1.10 g, 9.36mmol), 4-(hexyloxy)-N,N-bis (4-
iodophenyl) aniline (2.80 g, 4.68 mmol), copper powder (1.80 g,
28.1 mmol), potassium carbonate (6.46 g, 46.8 mmol), and 18-
crown-6 (37.1 mg, 0.14 mmol) in 1,2-dichlorobenzene (19 ml) was
heated at 180 8C for 48 h under an atmosphere of argon. After
cooled to room temperature, the inorganic components were
removed by filtration. The solvent was distilled under reduced
pressure and the crude product was purified with column
chromatography on silica gel using petroleum/ethyl acetate (20/
1)aseluenttoaffordawhitepowder(1.4 g,52%).(Found:C,83.21;H,
6.22; N, 7.08. C40H37N3OrequiresC, 83.45; H, 6.48;N, 7.30%);1H NMR
(300 MHz; CDCl3; TMS): 7.69 (2H, d, J 8.4 Hz, ArH), 7.57 (2H, d, J 8.4,
ArH),7.37(4H, d, J8.7, ArH),7.33(2H, d, J3.0, ArH),7.26–7.16(10H,m,
ArH), 6.93 (2H, d, J 9.0, ArH), 6.67 (2H, d, J 3.0, ArH), 3.98 (2H, t, J 6.6,
O—CH2), 1.81 (2H, m, CH2), 1.37–1.25 (6H, m, CH2), 0.92 (3H, t, J
6.6, CH3); 13C NMR (300 MHz; CDCl3; TMS): 156.6, 146.6, 140.1, 136.2,
134.0, 129.3, 128.3, 128.0, 125.6, 123.6, 122.5, 121.4, 120.4, 115.9,
110.8, 103.4, 68.5, 31.9, 29.6, 26.1, 22.9, 14.4; mp123–125 8C;m/z(EI)
575.3 (Mþ. C40H37N3O requires 575.3).
RESULTS AND DISCUSSION
Synthesis and structural characterization
As shown in Scheme 1, the four indole-based compounds (IIa–d)
were easily prepared by the Ullmann reaction between indole
and Ia–d, correspondingly. Indole was used directly without
purification, and Ia–d were easily synthesized according to the
J. Phys. Org. Chem. 2009, 22 241–246
Copyright ß 2008 John Wiley & Sons, Ltd.
www.interscience.wiley.com/journal/poc

Q. LI ET AL.
of 60% in the solvent mixture. A similar trend was found for IIb. To
exclude the possible influence from the organic solvent, two
other solvents, DMF and ethanol, were used instead of THF (Figs.
S23–S34). Similar results were obtained in the case of DMF: the
fluorescence intensity was initially increased upon increasing the
water fraction in the solvent mixture; however, it decreased when
the water fraction in the solvent mixture was further increased
(Figs. S23, S26, S29, and S32). These results confirmed that the
AIEE properties of IIa–d are not dependent on the organic
solvent. As shown in Figs. S24, S27, S30, and S33, when ethanol
was used instead of THF and DMF mixtures, the fluorescent
intensity of IIa–c decreased as the water fraction was increased in
the solvent mixture. The phenomena could be due to the poor
solubility of these luminophores in ethanol. This trend was not
observed for IId which showed similar behavior to that observed
in its THF and DMF mixtures, which can be attributed to the
greater solubility of IId in ethanol mixtures.
360 392 400
340
IIa
IIb
IIc
IId
320
380
440
500
Wavelength (nm)
As discussed above, in the mixture of organic solvent (THF,
DMF, or ethanol) and water, only the molecules on the surface of
the aggregates contributed to the detected fluorescence, many
molecules inside would not be excited and thus emit
fluorescence. Thus, in fact, the ‘true’ fluorescent intensity of
IIa–d should be much higher than those recorded in the mixture
solvent. In an attempt to observe the true fluorescence intensity
of IIa–d, we doped them into poly(methylmethacrylate) (PMMA)
with a concentration of 30%, then prepared thin films. As shown
in Figs. S35 and S36, the fluorescence intensities of their films
were much higher than those of the aggregation particles in the
solvent mixtures. The maximum emission wavelength of the thin
film of IIa was red-shifted by as much as 28 nm, indicating that
there were some p–p interactions between different molecules in
the solid state (we will discuss this later).
It is known that increasing the solvent viscosity can slow down
intramolecular rotations[53–55] or strengthen the RIR process. We
thus checked how variations in the viscosity would affect the
emission. The fluorescence intensities of IIa–d were increased by
adding glycerol, a viscous liquid, into their ethanol solutions
(Figs. 3 and S37–S40). It was easily seen that the fluorescent
intensities of IIa, IIb, and IId increased when the glycerol fraction
was increased from 10 to 90%. The decrease of the fluorescence
Figure 1. Normalized PL spectra of IIa–d in dilute THF solutions
molecular aggregates, in which restriction of intramolecular
rotations (RIR) leads to increased fluorescent emission. However,
further increase in the proportion of water in the solvent mixtures
resulted in a decrease of the fluorescence intensity. We postulate
that this phenomenon can be attributed to the decreasing
number of emissive molecules located at the surface of the
aggregates, relative to the non-emissive ones in their interiors, as
the aggregates increase in size, upon increasing amounts of
water being added to the mixtures. To support the above
discussion and exclude the possible precipitation effect of IId in
the mixed solvents, we tested its UV–Vis spectra in the mixed
solvents. As shown in Fig. S16, in most cases, the absorption
intensity are similar, indicating that there is no apparent
precipitation effect present.
Similar phenomena were observed in the behavior of the other
three indole-based molecules (Figs. 2B, and S17–S22). When a
small amount of water was added to the THF solution of IIa, its
emission intensity was increased immediately; it began to
decrease when the water fraction was more than 50%. The
fluorescent intensity of IIc reached a maximum at a water fraction
120
1.8
1.4
IIa
B
A
IIb
IIc
IId
Water fraction (vol%)
50
40
20
10
0
90
60
30
0
1.2
1.0
0.8
0.6
1.5
1.2
0.9
0.6
IIa
IIb
IIc
IId
350
400
450
500
0
30
60
90
Water fraction (vol%)
Wavelength (nm)
0
30
60
90
Figure 2. (A) PL spectra of the dilute solutions of IId in THF/water
mixtures with different water fraction. Concentration: 1.0 mM. Excitation
wavelength (nm): 329. (B) Changes in the PL peak intensities (I) of IIa–d
with different water fractions in the THF/water mixtures. Io ¼ intensity in
pure THF solution
Glycerol fraction (vol%)
Figure 3. Changes in PL peak intensities (I) of the solutions of IIa–d with
different glycerol fractions in glycerol/ethanol mixtures. Io ¼ intensity in
pure ethanol solution. Concentration: 1.0 mM
www.interscience.wiley.com/journal/poc
Copyright ß 2008 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2009, 22 241–246

INDOLE-CONTAINING LUMINOPHORES
intensity of IIc at high glycerol fraction should be ascribed to its
low solubility in glycerol. Thus, the viscosity proved that IIa–d
were AIEE active and the RIR process was indeed involved in the
AIEE system. That was to say, the restriction of the rotation of the
Carbon–Nitrogen bonds in IIa–d by the viscosity effect was
responsible for the observed AIEE behavior.
Thus, the above experimental results demonstrate that the four
indole-based dyes are AIEE active, confirming that the linkage of
different p-construction blocks through Carbon–Nitrogen bonds
could also yield AIE or AIEE molecules. Combined the fact that
through Carbon–Carbon bonds, different p-construction blocks,
as reported previously, could give AIE or AIEE dyes, it is expected
that the linkage of different p-construction blocks together might
result in AIE or AIEE luminophores, if the construction blocks
could rotate around the linking bonds.
Crystal structure and molecular stacking feature
To obtain some information about the structure of the indole-
based luminophores (IIa–d), we tried to grow single crystals of
them. While our efforts in growing the crystals of IIb and IId
failed, single crystals of Ia suitable for X-ray diffraction data
collection were obtained by recrystallization from acetone
solution (the Crystallographic data and refinement parameters
can be found in the Supporting Information). In the crystal
structure of Ia, the two indolyl groups and the benzene ring were
Figure 5. Packing diagram of IIa
luminophores could be designed through the linkage mode of
Carbon–Nitrogen bonds.
Figure 5 shows a perspective view of the packing arrange-
ments in the crystal of IIa. It is easily seen that there is some p–p
stacking between different molecules. The indolyl rings are
almost parallel, with adjacent indole moieties in two different
not co-planar, but twisted by 51.18 (Fig. 4). This phenomenon is
[32]
similar to those of 2,3,4,5-tetraphenylsiloles in solid state,
in
which the aryl peripheries were all out of planarity with the silole
core with typical dihedral angles of ꢁ308 for the ring positions
ortho to the silicon and larger twists of ꢁ708 at the meta positions
to the silicon atom. Thus, these facts indicated that the AIEE
behavior of IIa was not due to the planarization of the molecule
upon the formation of aggregate state, but the restrictions of the
intramolecular phenyl vibrational and rotational motions (around
Carbon–Nitrogen bonds). This point further confirmed that an
alternative approach to the design of new AIE (or AIEE)
luminophores is to utilize the linkage mode of Carbon–Nitrogen
bonds, with comparison to the mode of Carbon–Carbon bonds as
reported in most cases of AIE and AIEE luminophores. Therefore,
encouraged by our examples and examples reported in the
literature,[72] it can be assumed that many other AIE or AIEE
˚
molecules located at an average distance of 4.12 A apart. Similar
phenomena have been observed previously in the case of
carbazolyl moieties.[51,52] This could also explain the phenom-
enon of the much red-shifted maximum emission wavelength of
the thin film of IIa in PMMA, in comparison with that in dilute
solution. In the cases of IIb–d, there was no large difference of
the maximum emission wavelength between the thin films and
solutions, thus, there is likely to be no or weak interactions
between the indolyl groups of different molecules. This indicated
that the changing of the aromatic rings linked to the indolyl
group not only adjusts the maximum emission wavelength of the
resultant luminophores, but also affects their packing model in
the solid state. It would be useful to obtain the structures of IIb
and IId for comparison.
CONCLUSIONS
With the aim to broaden the family of AIE and AIEE luminophores,
a series of indole-based molecules were successfully and
conveniently synthesized. All of them possessed good thermal
stability and solubility, and demonstrated AIEE properties. By
simply changing the aromatic groups between two indolyl rings,
the maximum emission wavelength of the luminophores could
be tuned from 340 to 400 nm. Thus, the linkage mode of different
aromatic moieties through Carbon–Nitrogen bonds might be
useful for the development of new AIE and AIEE luminophores.
Coupled with their good biocompatible properties, the AIEE
indole-based luminophores might find some practical appli-
cations in the field of biology.
Figure 4. Molecular structure of IIa
J. Phys. Org. Chem. 2009, 22 241–246
Copyright ß 2008 John Wiley & Sons, Ltd.
www.interscience.wiley.com/journal/poc

Q. LI ET AL.
[34] H. Chen, W. Y. Lam, J. Luo, Y. Ho, B. Z. Tang, D. Zhu, M. Wong, H. S.
Kwok, Appl. Phys. Lett. 2002, 81, 574–576.
Acknowledgements
We are grateful to the National Science Foundation of China (no.
20402011, 20674059), the National Fundamental Key Research
Program, and Hubei Province for financial support.
[35] Y. Dong, J. W. Y. Lam, Z. Li, H. Tong, Y. Dong, X. Feng, B. Z. Tang, J. Inorg.
Organomet. Polym. Mater. 2005, 15, 287–291.
[36] M. Freemantle, Chem. Eng. News 2001, 79, 21–25.
[37] H. C. Yeh, S. J. Yeh, C. T. Chen, Chem Commun. 2003, 2632.
[38] C. J. Bhongale, C. S. Hsu, Angew. Chem. Int. Ed. 2006, 45, 1404–
1408.
REFERENCES
[39] W. Holzer, A. Penzkofer, R. Stockmann, H. Meysel, H. Liebegott, H. H.
Horhold, Polymer 2001, 42, 3183–3194.
[1] C. McDonagh, C. S. Burke, B. D. MacCraith, Chem. Rev. 2008, 108, 400–
422.
[2] D. Citterio, J. Takeda, M. Kosugi, H. Hisamoto, S. Sasaki, H. Komatsu, K.
Suzuki, Anal. Chem. 2007, 79, 1237–1242.
[40] S. Jayanty, T. P. Radhakrishnan, Chem. Eur. J. 2004, 10, 791–797.
[41] Z. Wang, H. Shao, J. Ye, L. Tang, P. Lu, J. Phys. Chem. B 2005, 109,
19627–19633.
[42] K. Itami, Y. Ohashi, J. Yoshida, J. Org. Chem. 2005, 70, 2778–2792.
[43] M. Han, M. Hara, J. Am. Chem. Soc. 2005, 127, 10951–10955.
[44] H. J. Tracy, J. L. Mullin, W. T. Klooster, J. A. Martin, J. Haug, S. Wallace, I.
Rudloe, K. Watts, Inorg. Chem. 2005, 44, 2003–2011.
[45] K. Itami, J. Yoshida, Chem. Eur. J. 2006, 12, 3966–3974.
[46] C. Belton, D. F. O’Brien, W. J. Blau, A. J. Cadby, P. A. Lane, D. D. C.
Bradley, H. J. Bryne, R. Stockmann, H. H. Horhold, Appl. Phys. Lett.
2001, 78, 1059–1061.
´
[3] M. Barauh, W. Qin, R. A. L. Vallee, D. Beljonne, R. Rohand, W. Dehaen,
N. Boens, Org. Lett. 2005, 7, 4377–4380.
[4] C. R. Taitt, G. P. Anderson, B. M. Lingerfelt, M. J. Feldstein, F. S. Ligler,
Anal. Chem. 2002, 74, 6114–6120.
¨
[5] A. Hayer, V. de Halleux, A. Kohler, A. El-Garoughy, E. W. Meijer, J.
Barber, J. Tant, J. Levin, M. Lehmann, J. Gierschner, J. Cornil, Y. H.
Geerts, J. Phys. Chem. B 2006, 110, 7653–7659.
[6] F. S. Ligler, K. W. Sapsford, J. P. Golden, L. C. Shriver-Lake, C. R. Taitt,
M. A. Dyer, S. Baraone, C. J. Myatt, Anal. Sci. 2007, 23, 5–10.
[7] W. C. Tse, D. L. Boger, Acc. Chem. Res. 2004, 37, 61–69.
[8] I. L. Medintz, H. T. Uyeda, E. R. Goldman, H. Mattoussi, Nat. Mater.
2005, 4, 435–446.
[9] M. W. Peczuh, A. D. Hamilton, Chem. Rev. 2000, 100, 2479–2494.
[10] C. T. Chen, C. L. Chiang, Y. C. Lin, L. H. Chan, C. H. Huang, Z. W. Tsai, C. T.
Chen, Org. Lett. 2003, 5, 1261–1265.
[11] A. Wakamiya, K. Mori, S. Yamaguchi, Angew. Chem. Int. Ed. 2007, 46,
4273–4279.
[12] H. Langhals, O. Krotz, K. Polborn, P. Mayer, Angew. Chem. Int. Ed. 2005,
117, 2479–2494.
[47] S. Yin, Q. Peng, Z. Shuai, W. Fang, Y. H. Wang, Y. Luo, Phys. Rev. B 2006,
73, 205409–205413.
[48] Y. Ren, J. W. Y. Lam, Y. Dong, B. Z. Tang, K. S. Wong, J. Phys. Chem. B
2005, 109, 1135–1140.
[49] Y. Ren, Y. Dong, J. W. Y. Lam, B. Z. Tang, K. S. Wong, Chem. Phys. Lett.
2005, 402, 468–473.
[50] Z. Li, Y. Dong, B. Mi, Y. Tang, M. Ha¨ussler, H. Tong, Y. Dong, J. W. Y. Lam,
Y. Ren, H. H. Y. Sung, K. S. Wong, P. Gao, I. D. Williams, H. S. Kwok, B. Z.
Tang, J. Phys. Chem. B 2005, 109, 10061–10066.
[51] H. Tong, Y. Hong, Y. Dong, M. Ha¨ussler, J. W. Y. Lam, Z. Li, Z. Guo, Z. Guo,
B. Z. Tang, Chem. Commun. 2006, 3705–3707.
[52] Q. Zeng, Z. Li, Y. Dong, L. Ji, C. Di, A. Qin, Y. Hong, Z. Zhu, C. K. W.
Jim, G. Yu, Q. Li, Z. Li, Y. Liu, J. Qin, B. Z. Tang, Chem. Commun.
2007, 70–72.
[13] S. H. Lee, B.-B. Jang, Z. H. Kafafi, J. Am. Chem. Soc. 2005, 127, 9071–
9078.
[14] Y. Kim, J. Bouffard, S. E. Kooi, T. M. Swager, J. Am. Chem. Soc. 2005, 127,
13726–13731.
[53] Y. Dong, J. W. Y. Lam, A. Qin, Z. Li, J. Liu, J. Sun, Y. Dong, B. Z. Tang,
Chem. Phys. Lett. 2007, 446, 124–127.
[15] Z. Xie, B. Yang, F. Li, G. Cheng, L. Liu, G. Yang, H. Xu, L. Ye, M. Hanif, S.
Liu, D. Ma, Y. Ma, J. Am. Chem. Soc. 2005, 127, 14152–14153.
[16] H. Murata, Z. H. Kafafi, M. Uchida, Appl. Phys. Lett. 2002, 80, 189–191.
[17] S. J. Toal, K. A. Jones, D. Magde, W. C. Trogler, J. Am. Chem. Soc. 2005,
127, 11661–11665.
[18] Z. Xie, B. Yang, W. Xie, L. Liu, F. Shen, H. Wang, X. Yang, Z. Wang, Y. Li, M.
Hanif, G. Yang, L. Ye, Y. Ma, J. Phys. Chem. B 2006, 110, 20993–21000.
[19] C. J. Bhongale, C. W. Chang, C. S. Lee, E. W. G. Diau, C. S. Hsu, J. Phys.
Chem. B 2005, 109, 13472–13478.
[20] S. A. Jenekhe, J. A. Osaheni, Science 1994, 265, 765–768.
´
[21] J. Cornil, D. A. dos Santos, X. Crispin, R. Silbey, J. L. Bredas, J. Am. Chem.
Soc. 1998, 120, 1289–1299.
[22] X. Liu, C. He, X. Hao, L. Tan, Y. Li, K. S. Ong, Macromolecules 2004, 37,
[54] H. Tong, Y. Hong, Y. Dong, M. Ha¨ussler, Z. Li, J. W. Y. Lam, Y. Dong,
H. H. Y. Sung, I. D. Williams, B. Z. Tang, J. Phys. Chem. B 2007, 111,
11817–11823.
[55] Y. Hong, M. Ha¨ussler, J. W. Y. Lam, Z. Li, K. K. Sin, Y. Dong, H.
Tong, J. Liu, A. Qin, R. Renneberg, B. Z. Tang, Chem. Eur. J. 2008,
14, 6428–6437.
[56] C. Guan, J. Ju, B. R. Borlee, L. L. Williamson, B. Shen, K. F. Raffa, J.
Handelsman, Appl. Environ. Microbiol. 2007, 73, 3669–3676.
[57] S. Lee, M. Flores-Encarnacion, M. Contreras-Zentella, L. Garcia-Flores,
J. E. Escamilla, C. J. Kennedy, Bacteriol. 2004, 186, 5384–5391.
[58] I. Sjoholm, I. Ljungstedt, J. Bio. Chem. 1973, 248, 3434–3438.
[59] F. Mohammadi, G. A. Prentice, A. R. Merrill, Biochem. 2001, 40, 10273–
10283.
5965–5970.
[23] S. Hecht, J. M. J. Frechet, Angew. Chem. Int. Ed. 2001, 40, 74–91.
[60] M. E. Bush, N. D. Bouley, A. R. Urbach, J. Am. Chem. Soc. 2005, 127,
14511–14517.
´
[24] A. W. Freeman, S. C. Koene, P. R. L. Malenfant, M. E. Thompson, J. M. J.
[61] G. W. Gribble, J. Chem. Soc., Perkin Trans. 1 2000, 1045–1075.
[62] S. Cacchi, G. Fabrizi, Chem. Rev. 2005, 105, 2873–2920.
[63] Q. Li, Z. Li, C. Ye, J. Qin, J. Phys. Chem. B 2008, 112, 4928–4933.
[64] Q. Li, Z. Li, F. Zeng, W. Gong, Z. Li, Z. Zhu, Q. Zeng, S. Yu, C. Ye, J. Qin,
J. Phys. Chem. B 2007, 111, 508–514.
[65] W. Gong, Q. Li, Z. Li, C. Lu, J. Zhu, S. Li, J. Yang, Y. Cui, J. Qin, J. Phys.
Chem. B 2006, 110, 10241–10247.
[66] Z. Li, C. Huang, J. Hua, J. Qin, Z. Yang, C. Ye, Macromolecules 2004, 37,
371–376.
´
Frechet, J. Am. Chem. Soc. 2000, 122, 12385–12386.
[25] L. H. Chan, R. H. Lee, C. F. Hsieh, H. C. Yeh, C. T. Chen, J. Am. Chem. Soc.
2002, 124, 6469–6479.
[26] S. Wang, W. J. Oldham, R. A. Hudack, Jr., G. C. Bazan, Jr., J. Am. Chem.
Soc. 2000, 122, 5695–5709.
[27] Y. Li, J. Ding, M. Day, T. Tao, J. Lu, M. D’iorio, Chem. Mater. 2003, 15,
4936.
[28] F. Cherious, L. Guyard, Adv. Funct. Mater. 2003, 11, 305–308.
[29] R. Deans, J. Kim, M. R. Machacek, T. M. Swager, J. Am. Chem. Soc. 2000,
122, 8565–8566.
[67] Z. Li, J. Qin, S. Li, C. Ye, J. Luo, Y. Cao, Macromolecules 2002, 35, 9232–
9235.
[30] B. K. An, S. K. Kwon, S. D. Jung, S. Y. Park, J. Am. Chem. Soc. 2002, 124,
14410–14415.
[68] K. Albrecht, Y. Kasai, A. Kimoto, K. Yamamoto, Macromolecules 2008,
41, 3793–3800.
[31] J. Luo, Z. Xie, J. W. Y. Lam, L. Cheng, H. Chen, C. Qiu, H. S. Kwok, X.
Zhan, Y. Liu, D. Zhu, B. Z. Tang, Chem. Commun. 2001, 1740–1741.
[32] J. Chen, C. C. W. Law, J. W. Y. Lam, Y. Dong, S. M. F. Lo, I. D. Williams, D.
Zhu, B. Z. Tang, Chem. Mater. 2003, 15, 1535–1637.
[33] G. Yu, S. Yin, Y. Liu, J. Chen, X. Xu, X. Sun, D. Ma, X. Zhan, Q. Peng, Z.
Shuai, B. Z. Tang, D. Zhu, W. Fang, Y. Luo, J. Am. Chem. Soc. 2005, 127,
6335–6346.
[69] S. C. Suh, S. C. Shim, D. J. Yoo, J. Photosci. 2003, 10, 251–255.
[70] S. Wakim, J. Bouchard, N. Blouin, A. Michaud, M. Leclerc, Org. Lett.
2004, 6, 3413–3416.
[71] S. Grigalevicius, J. V. Grazulevicius, V. Gaidelis, V. Jankanskas, Polymer
2002, 43, 2603–2608.
[72] Z. Ning, Z. Chen, Q. Zhang, Y. Yan, S. Qian, Y. Cao, H. Tian, Adv. Funct.
Mater. 2007, 17, 3799–3807.
www.interscience.wiley.com/journal/poc
Copyright ß 2008 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2009, 22 241–246