Multifunctional organic fluorescent materials derived from 9,10-distyrylanthracene with alkoxyl endgroups of various lengths

Article abstract of DOI:10.1039/c2cc36263e

A series of remarkable multifunctional 9,10-distyrylanthracene derivatives (DSA_n, n = 7-12) was synthesized. All derivatives possess typical aggregation-induced emission (AIE) property. Some of the derivatives exhibit multifunctional properties, including AIE, mechanofluorochromism, vapochromism, thermochromism, and mesomorphism, which are rarely found to exist simultaneously in a single compound.

Full text of DOI:10.1039/c2cc36263e

View Online / Journal Homepage
Dynamic Article Links
ChemComm
Cite this: DOI: 10.1039/c2cc36263e
www.rsc.org/chemcomm
COMMUNICATION
Multifunctional organic fluorescent materials derived from
9,10-distyrylanthracene with alkoxyl endgroups of various lengthsw
Xiqi Zhang,a Zhenguo Chi,*a Bingjia Xu,a Long Jiang,a Xie Zhou,b Yi Zhang,a Siwei Liua
and Jiarui Xua
Received 28th August 2012, Accepted 17th September 2012
DOI: 10.1039/c2cc36263e
A series of remarkable multifunctional 9,10-distyrylanthracene
derivatives (DSAn, n = 7–12) was synthesized. All derivatives
possess typical aggregation-induced emission (AIE) property.
Some of the derivatives exhibit multifunctional properties,
Scheme 1 Chemical structure of DSAn.
including AIE, mechanofluorochromism, vapochromism, thermo-
chromism, and mesomorphism, which are rarely found to exist
simultaneously in a single compound.
However, the PL intensity was significantly enhanced when the
water fraction exceeded 40%. The PL intensity in pure THF
was 5.4 a.u., which increased to B295.8 a.u. in the 60%
water–THF mixture, showing an approximately 55-fold
enhancement. The ultraviolet–visible absorption spectra
(UV-vis) of DSA11 in the water–THF mixtures are shown in
Fig. 1b. The spectral profile was virtually unchanged even
when a water fraction of up to 40% was added to the THF
solution. With the further increased water fraction, the entire
spectrum started to rise. The increase of the absorbance in the
entire spectral region was caused by the Mie effect6 of the
nano-aggregate suspensions in the solvent mixtures. The result
showed that the DSA11 molecules started to aggregate markedly
when the mixture contained 40% of water. The PL and UV-vis
results were in good agreement. These results confirmed that the
compound had a significant AIE effect caused by the formation
of molecular aggregates upon the addition of water to the
solution. Similar phenomena were observed for the other
compounds (Fig. S1 and S2, ESIw).
Most organic luminescent materials exhibit very strong lumi-
nescence in their dilute solutions. However, their light emissions
dramatically decrease because of increased solution concen-
tration or aggregation in the solid states, resulting from strong
intermolecular p–p stacking interactions and nonradiative
decay. This phenomenon is well known as the aggregation-
caused quenching (ACQ).1 The ACQ effect has greatly limited the
applications of organic luminescent materials and has driven
researchers to seek anti-ACQ materials with higher efficiency in
the aggregated state than in the dissolved state. Some anti-ACQ
materials have been reported by Tang et al.2 and Park et al.3 in
2001 and 2002, respectively, and were called aggregation-induced
emission (AIE) or aggregation-induced emission enhancement
(AIEE) materials. Since then, AIE or AIEE materials have been
found promising as emitters for the fabrication of highly efficient
electroluminescent devices and as stimuli-responsive materials of
probes.4 Since 2010, many AIE materials were reported to possess
mechanofluorochromic properties.5 Herein, a series of compounds,
DSAn (n = 7 to 12; Scheme 1), was synthesized and found to
exhibit at least five functions: AIE, mechanofluorochromism,
vapochromism, thermochromism, and mesomorphism.
The PL intensities of all the compounds decreased in the
THF–water mixtures containing 50% and/or 60% of water.
AIE phenomenon: as shown in Fig. 1a, DSA11 in pure
THF exhibited a very weak photoluminescence (PL) intensity.
a PCFMLab, DSAPM Lab, KLGHEIof Environment and Energy
Chemistry, State Key Laboratory of Optoelectronic Materials and
Technologies, School of Chemistry and Chemical Engineering,
Sun Yat-sen University, Guangzhou 510275, P. R. China.
E-mail: chizhg@mail.sysu.edu.cn; Fax: +86 20 84112222;
Tel: +86 20 84112712
Fig. 1 (a) PL spectra of the dilute solutions of DSA11 (10 mM) in
water–THF mixtures with different volume fractions of water (excita-
tion wavelength = 365 nm). The top inset shows the changes in the PL
peak intensity. The bottom inset shows the emission images of DSA11
(10 mM) in pure THF as well as 60%, 70%, and 90% water fraction
mixtures under 365 nm UV illumination; (b) UV-vis absorption
spectra of the dilute solutions of DSA11 (10 mM) in water–THF
mixtures with different volume fractions of water.
b School of Pharmaceutical Sciences, Sun Yat-sen University,
Guangzhou 510275, P. R. China
w Electronic supplementary information (ESI) available: Experimental
details; Tables S1 and S2; Fig. S1–S14; Video S1, 1H NMR, 13C NMR
and MS spectra (Fig. S15–S32); crystallographic data (Tables S3–S8)
(PDF). CCDC 886641–886646. For ESI and crystallographic data in
CIF or other electronic format see DOI: 10.1039/c2cc36263e
c
This journal is The Royal Society of Chemistry 2012
Chem. Commun.

View Online
interactions including Ph - O, Ph - Ph, Ph - An, Oct - Ph,
An - An, An - Ph, and Vin - An. Among these supra-
molecular interactions, CH–p interactions were the most
important. The backbone of the molecules largely deviated
from a plane, and typical cofacial p–p stacking became
impossible because of the highly twisted conformation as well
as steric hindrance of the bulky aromatic rings in the molecules.
Thus, only DSA8 and DSA9 crystals exhibited weak face-to-face
p-stacking of anthracene rings with small p-overlap areas and
contact distances of about 3.64 A (DSA8) and 3.56 A (DSA9). As
listed in Table S2 (also see Fig. S5, ESIw), DSA7, DSA8, and
DSA9 crystals showed four, five, and four interactions; whereas
DSA10, DSA11, and DSA12 crystals showed only one, two, and
two supramolecular interactions, respectively. This result indi-
cated that the supramolecular interactions in the former three
crystals were stronger than those in the latter three crystals. The
strong supramolecular interactions not only made the molecule
more planar and stable in the lattice, but also induced tight
intermolecular packing (Fig. S6, ESIw). The density d of
DSA7, DSA8, and DSA9 crystals ranged from 1.167 g cmꢀ3
to 1.185 g cmꢀ3; for DSA10, DSA11, and DSA12 crystals, d ranged
from 1.127 g cmꢀ3 to 1.146 g cmꢀ3, respectively. These results
indicated that the more twisted conformation and weaker supra-
molecular interactions in DSA10, DSA11, and DSA12 crystals
relatively loosened the molecular packing and resulted in lower
lattice energies. The two structural features rendered the crystals
easily destructible under external pressure. This is probably the
reason why DSA10, DSA11, and DSA12 exhibited more significant
mechanofluorochromism as compared to others.
Fig. 2 (a) Normalized PL spectra of DSA11 before and after grinding,
and (b) wavelength change versus n after grinding. Inset images: DSA11
cast on a filter paper, with ‘‘AnPC11’’ written using a metal spatula at
room temperature under UV light; images of the compounds before
and after grinding under 365 nm UV illumination.
This phenomenon is often observed in some compounds with
AIE properties, but the reasons remain unclear.7
Mechanofluorochromism: DSA10, DSA11, and DSA12 showed
significant changes in emission when they were ground, i.e., red
shifting by 45, 45, and 52 nm, respectively (Table S1 and Fig. S3,
ESIw). For example, the as-synthesized DSA11 showed a strong
green emission (498 nm) under 365 nm UV light. After grinding,
the sample showed a strong yellow emission (543 nm) with a
45 nm red-shift (Fig. 2a). These results indicated that DSA10,
DSA11, and DSA12 have a color-switchable feature that has
potential use in optical recording and pressure-sensing materials.
However, DSA7, DSA8, and DSA9 exhibited insignificant
mechanofluorochromism. After grinding, their emissions red
shifted by only 4, 10, and 12 nm, respectively (Fig. 2b).
The X-ray structural analysis of the single crystals revealed
%
that the compounds crystallized in the triclinic space group P1.
Powder wide-angle X-ray diffraction measurements revealed
the significantly different molecular packing structures of DSA10,
DSA11, and DSA12 before and after grinding (Fig. S7, ESIw). The
diffraction patterns of the as-synthesized samples displayed some
sharp and intense reflections, which indicated some crystalline
order. After grinding, the reflections remarkably weakened,
indicating decrease in crystalline order. Notably, the three
original samples had a strong reflection peak near 2y = 101,
which almost disappeared after grinding. However, DSA7,
DSA8, and DSA9 had no such strong reflection peaks and
their diffraction patterns changed little from their original
forms after grinding. This finding further confirmed that
the significant mechanofluorochromic properties of DSA10,
DSA11, and DSA12 were caused by the change in crystalline
order.
The selected dihedral angles between two phenyl rings and the
anthryl ring, yA–B and yB–C (defined in Fig. S4, ESIw), are
listed in Table S2 (ESIw). Analysis of the crystal structures of
the compounds demonstrated that they have a nonplanar
conformation in their crystals. The dihedral angle values in the
molecular structures of the compounds optimized at the DFT
B3LYP/6-31G level8 were the same, i.e., yA–B and yB–C are equal
to 601. However, in their single crystals, the dihedral angles
significantly differed. The conformation structures of DSA10,
DSA11, and DSA12 were symmetrical; thus, the yA–B values were
equal to yB–C and the values were 761, 701, and 741, respectively.
These values are greater than 601, considering that the larger
dihedral angles of the molecules were responsible for the shorter
PL wavelengths (from 498 nm to 500 nm) in their original states.
However, DSA7 and DSA8 crystals had two distinct conforma-
tion structures, namely, symmetric and asymmetric. In DSA7
crystals, yA–B and yB–C were 581 in the symmetric conformation
structure, and 281 and 661 in the asymmetric conformation
structure. In DSA8 crystals, yA–B and yB–C were 561 in the
symmetric conformation structure, and 281 and 741 in the
asymmetric conformation structure. DSA9 crystals had only
an asymmetric conformation structure with yA–B = 401 and
yB–C = 501. In general, the dihedral angles of DSA7, DSA8,
and DSA9 were smaller than those of DSA10, DSA11, and
DSA12. Consequently, the former three compounds in their
original states exhibited longer PL wavelengths (from 515 nm
to 531 nm). The analysis of the crystal structures showed that
the above mentioned difference among the molecular confor-
mation structures of the crystals was caused by supramolecular
All the original compounds exhibited two marked exo-
thermic transition peaks in heating differential scanning
calorimetry (DSC) curves. One peak at the lower temperature
was ascribed to the phase transition from solid crystalline to
liquid crystal, TS-LC, and the other peak at the higher temperature
was ascribed to the phase transition from liquid crystal to
isotropic melt, Ti. Grinding markedly affected the TS-LC values
of DSA10, DSA11, and DSA12, including the position and
shape of the transition peak, but hardly affected the Ti
transition. For DSA7, DSA8, and DSA9, almost no change
in the two peaks was observed after grinding (Fig. S8, ESIw).
The DSC results also indicated that grinding did significantly
change the morphologies of DSA10, DSA11, and DSA12.
The weighted mean lifetimes hti are listed in Table S1
(ESIw). The hti values of DSA7, DSA8, and DSA9 before
c
Chem. Commun.
This journal is The Royal Society of Chemistry 2012

View Online
In summary, a series of remarkable multifunctional 9,10-
distyrylanthracene derivatives (DSAn, n = 7–12) was success-
fully synthesized. All the derivatives are AIE compounds.
When n Z 10, the derivatives exhibit significant mechano-
fluorochromism. Supramolecular interaction was found to play
an important role in determining the mechanofluorochromism.
All the derivatives also exhibit vapochromism, thermochromism,
and mesomorphism. These attributes may enable the application
of these novel compounds in a wide range of fields, including
optical displays, chemosensors, rewritable optical media,
stress sensors, thermal sensors, among others.
Fig. 3 Reversible color changes of DSA11 upon heating and cooling.
and after grinding were similar, and their time-resolved
fluorescence curves almost coincided with one another (Fig. S9,
ESIw). By contrast, the hti values of the original and ground
DSA10, DSA11, and DSA12 samples significantly differed: 1.22,
1.35, and 1.22 ns for the original samples; 3.42, 3.75, and
3.57 ns for the ground samples, respectively. These results
showed that the time-resolved emission-decay behaviors of
the original and ground compounds were distinctly changed
when the materials showed significant mechanofluorochromic
properties.
The authors gratefully acknowledge the financial support
from the National Natural Science Foundation of China
(51173210, 51073177), the Science and Technology Planning
Project of Guangdong Province, China (Grant numbers:
2007A010500001-2), Construction Project for University-
Industry cooperation platform for Flat Panel Display from The
Commission of Economy and Informatization of Guangdong
Province (Grant number: 20081203), the Fundamental Research
Funds for the Central Universities and Natural Science Foun-
dation of Guangdong (S2011020001190).
Thermochromism: all the compounds were found to possess
thermochromic properties. As an example, a star-like pattern
was stamped on a filter paper soaked in DSA11 solution in
CH2Cl2. After drying, the pattern emitted green light (514 nm)
under 365 nm UV illumination. As the pattern was heated to
the Ti transition of DSA11 using a hot air gun, its emission
quickly changed to dark yellow (566 nm) and the variation in
the emission wavelength reached 52 nm. As soon as the hot air
gun was removed, the green emission pattern was immediately
recovered, showing the excellent reversibility of the phenomenon
(Fig. 3 and Video S1, ESIw). The temperature-dependent PL
results of DSA11 are shown in Fig. S10 (ESIw).
Notes and references
1 (a) R. H. Friend, R. W. Gymer, A. B. Holmes, J. H. Burroughes,
R. N. Marks, C. Taliani, D. D. C. Bradley, D. A. Dos Santos,
J. L. Bredas, M. Logdlund and W. R. Salaneck, Nature, 1999,
397, 121; (b) S. A. Jenekhe and J. A. Osaheni, Science, 1994,
265, 765; (c) C. T. Chen, Chem. Mater., 2004, 16, 4389.
2 J. D. Luo, Z. L. Xie, J. W. Y. Lam, L. Cheng, H. Y. Chen,
C. F. Qiu, H. S. Kwok, X. W. Zhan, Y. Q. Liu, D. B. Zhu and
B. Z. Tang, Chem. Commun., 2001, 1740.
Vapochromism: all the compounds exhibited vapochromism
in their solid states. For example, under UV illumination
(wavelength = 365 nm) at room temperature, a spot of
DSA11 on the thin-layer chromatography (TLC) plate showed
bright green fluorescence, which was reversibly switched off in
an atmosphere of CH2Cl2 (Fig. S11, ESIw) or other viable
solvent vapors. One probable explanation was that the solva-
tion of the vapor of the appropriate solvent disrupted the
interaction of solid molecules to a significant extent, resulting
in the free rotation of the single bonds of the AIE molecules,
which led to non-emission. The compounds possessed a
reversible on–off fluorescence switching property in some
organic vapors. Therefore, these compounds may be used as
chemical vapor sensors in the photoswitch field, which may be
one of their most important potential applications.
3 B. K. An, S. K. Kwon, S. D. Jung and S. Y. Park, J. Am. Chem.
Soc., 2002, 124, 14410.
4 (a) Y. N. Hong, J. W. Y. Lam and B. Z. Tang, Chem. Commun.,
2009, 4332; (b) Y. S. Zhao, H. B. Fu, A. D. Peng, Y. Ma, D. B. Xiao
and J. N. Yao, Adv. Mater., 2008, 20, 2859; (c) B. J. Xu, Z. G. Chi,
Z. Y. Yang, J. B. Chen, S. Z. Deng, H. Y. Li, X. F. Li, Y. Zhang,
N. S. Xu and J. R. Xu, J. Mater. Chem., 2010, 20, 4135; (d) H. Y. Li,
Z. G. Chi, B. J. Xu, X. Q. Zhang, Z. Y. Yang, X. F. Li, S. W. Liu,
Y. Zhang and J. R. Xu, J. Mater. Chem., 2010, 20, 6103; (e) Z. Y. Yang,
Z. G. Chi, B. J. Xu, H. Y. Li, X. Q. Zhang, X. F. Li, S. W. Liu,
Y. Zhang and J. R. Xu, J. Mater. Chem., 2010, 20, 7352.
5 (a) B. J. Xu, Z. G. Chi, X. Q. Zhang, H. Y. Li, C. J. Chen, S. W. Liu,
Y. Zhang and J. R. Xu, Chem. Commun., 2011, 47, 11080; (b) H. Y. Li,
X. Q. Zhang, Z. G. Chi, B. J. Xu, W. Zhou, S. W. Liu, Y. Zhang and
J. R. Xu, Org. Lett., 2011, 13, 556; (c) X. Q. Zhang, Z. G. Chi,
H. Y. Li, B. J. Xu, X. F. Li, W. Zhou, S. W. Liu, Y. Zhang and
J. R. Xu, Chem.–Asian J., 2011, 6, 808; (d) X. Q. Zhang, Z. G. Chi,
J. Y. Zhang, H. Y. Li, B. J. Xu, X. F. Li, S. W. Liu, Y. Zhang and
J. R. Xu, J. Phys. Chem. B, 2011, 115, 7606; (e) S. J. Yoon,
J. W. Chung, J. Gierschner, K. S. Kim, M. G. Choi, D. Kim and
S. Y. Park, J. Am. Chem. Soc., 2010, 132, 13675; (f) X. L. Luo, J. N. Li,
C. H. Li, L. P. Heng, Y. Q. Dong, Z. P. Liu, Z. S. Bo and B. Z. Tang,
Adv. Mater., 2011, 23, 3261; (g) C. D. Dou, L. Han, S. S. Zhao,
H. Y. Zhang and Y. Wang, J. Phys. Chem. Lett., 2011, 2, 666;
(h) X. Q. Zhang, Z. G. Chi, B. J. Xu, C. J. Chen, X. Zhou,
Y. Zhang, S. W. Liu and J. R. Xu, J. Mater. Chem., 2012, 22, 18505.
Mesomorphism: the DSC results showed that all the original
samples had two endothermic peaks in the first heating process
(Fig. S12, ESIw), indicating that two phases were present
before isotropic melting. The peak at the higher temperature
corresponding to Ti ranged from 166 1C to 129 1C. When
n o 10, Ti decreased with increased n. When n Z 10,
Ti became independent of the chain length. However, the peak
at the lower temperature (TS-LC) strongly depended on the
chain length and exhibited a zigzag pattern, showing a signi-
ficant odd–even effect (Fig. S13, ESIw). This finding suggested
that the direction of the chain-end can affect the molecular
packing in the solid state and the thermal transition behavior.
A colored birefringence-like thermotropic liquid crystalline
texture appeared when the isotropic melt was cooled to below
130 1C (Fig. S14, ESIw).
6 H. Tong, Y. Q. Dong, M. Haubler, J. W. Y. Lam, H. H. Y. Sung,
¨
I. D. Williams, J. Z. Sun and B. Z. Tang, Chem. Commun., 2006,
1133.
7 (a) S. C. Dong, Z. Li and J. G. Qin, J. Phys. Chem. B, 2009,
113, 434; (b) Z. Y. Yang, Z. G. Chi, T. Yu, X. Q. Zhang,
M. N. Chen, B. J. Xu, S. W. Liu, Y. Zhang and J. R. Xu,
J. Mater. Chem., 2009, 19, 5541; (c) X. Q. Zhang, Z. G. Chi,
B. J. Xu, H. Y. Li, Z. Y. Yang, X. F. Li, S. W. Liu, Y. Zhang
and J. R. Xu, Dyes Pigm., 2011, 89, 56.
8 M. J. Frisch, G. W. Trucks and H. B. Schlegel, et al., Gaussian 03,
Revision D.01, Gaussian, Inc., Wallingford, CT, 2004.
c
This journal is The Royal Society of Chemistry 2012
Chem. Commun.