DOI: 10.1002/chem.201402152
Communication
&
Aggregation-Induced Emission
An Efficient AIE-Active Blue-Emitting Molecule by Incorporating
Multifunctional Groups into Tetraphenylsilane**
Xiangyang Tang, Liang Yao, He Liu, Fangzhong Shen, Shitong Zhang, Huanhuan Zhang,
Ping Lu,* and Yuguang Ma[a]
been carried out to enhance the performance of TPE deriva-
Abstract: A multifunctional AIE-active molecule, CzPy-
SiTPE, in which carbazole (Cz) and pyridine (Py) were at-
tives.[8] However, most of the resultant compounds demon-
strated high device efficiency at the expense of red shifting
tached to tetraphenylsilane to facilitate carrier injection
the emission to light green, or an even longer wavelength, as
has been designed and synthesized. Tetraphenylethene
a result of prolonged electronic conjugation or strong charge-
(TPE) was adopted to maintain efficient blue emission.
transfer effects. Thus, it is quite challenging to improve TPE-
Blue electroluminescent (EL) emission of CzPySiTPE was
device performance without sacrificing its blue emission. First-
obtained with CIE coordinates of (0.16, 0.17) and an exter-
ly, to enhance the device performance, it is pivotal to lower
nal quantum efficiency of 1.12%.
the charge injection barriers and balance the carriers transport.
An effective way to fulfill this goal is to introduce hole/elec-
tron-transport groups simultaneously.[9] Secondly, to gain real
Design and synthesis of highly efficient solid-state organic ma-
terials is of fundamental importance, and has technical implica-
tions because most of the materials are applied as thin films,
or in aggregate states, in optoelectronic devices.[1] Particularly,
with the development of organic light-emitting diodes (OLEDs)
in the past years, red- and green-emitters have shown out-
standing performances in terms of luminance and efficiency[2]
However, the development of blue emitters remains to be
a challenge.[3] Although traditional blue fluorophores, such as
anthracene,[4a] fluorene,[4b] and triphenylamine[4c] derivatives,
are highly emissive in dilute solutions, they suffer from the no-
torious effect of aggregation-caused quenching (ACQ). A
number of methods, such as the spiro approach, have been
applied to overcome the ACQ problem and some positive re-
sults have been reported.[5] Particularly, a chromophore called
tetraphenylethene (TPE),[6a] reported by Tang et al.,[6] can natu-
rally overcome the problem of ACQ and possesses the aggre-
gation-induced-emission (AIE) feature. This chromophore is
non-luminescent in dilute solution, but exhibits strong blue
emission in aggregate states. The AIE effect was interpreted as
the restriction of intramolecular rotation (RIR) in the solid
state.[6b] Both the blue emission and extremely high solid-state
luminous efficiency make TPE an ideal candidate for blue-OLED
applications.
blue emission of the TPE unit, it is critical to restrict the conju-
gation of TPE, that is to say, the effective conjugation length
should be the same as that of TPE, even the conjugation of an
extra phenyl group can generate light-green emission. Howev-
er, an issue arises regarding how to connect the hole/electron-
transport groups and the emitter, TPE, into one molecule, with-
out extending the conjugation of the TPE moiety. A medium
that can work as a bridge, linking hole/electron transport
groups and TPE, and as an insulator to efficiently interrupt con-
jugation length is needed. Recently, some intriguing properties
of tetraphenylsilane have been reported by our group and
may shed light on the above issue.[10] Tetraphenylsilane pos-
sesses a tetrahedral configuration, resulting from the sp3 hy-
bridization of the Si atom, and occupies a relatively large
space.[11] With these characteristics, tetraphenylsilane can effi-
caciously interrupt the conjugation and avoid intramolecular
charge transfer. Thus, tetraphenylsilane can act as an appropri-
ate insulator. On the other hand, tetraphenylsilane is also
a multidirectional bridge. Through the chemical reaction be-
tween 1,4-dibromobenzene and Ph(4Àx)SiClx (x=1, 2, 3, or 4),
any phenyl group of tetraphenylsilane can be provided with
active reaction sites. From the point of synthetic chemistry, it is
possible to add three different functional groups to the tetra-
phenylsilane core by classical coupling reactions. Inspired by
these ideas, we designed and synthesized an AIE-active mole-
cule, CzPySiTPE, in which carbazole (Cz), pyridine (Py), and TPE
groups are linked by a tetraphenylsilane core. The design strat-
egy aims to afford adducts with the combined merits of the
carbazole, pyridine, and TPE unit,[6,12] facilitating the carrier in-
jection and transport and keeping the blue emission of TPE
intact. For a more comprehensive study, SiTPE, CzSiTPE, and
PySiTPE were also synthesized (Scheme 1).
TPE alone shows very poor device performance with a cur-
rent efficiency of only 0.45 cdAÀ1 (corresponding to an external
quantum efficiency of 0.4%).[7] Intense investigations have
[a] Dr. X. Tang, Dr. L. Yao, Dr. H. Liu, Dr. F. Shen, Dr. S. Zhang, Dr. H. Zhang,
Prof. P. Lu, Prof. Y. Ma
State Key Laboratory of Supramolecular Structure and Materials
Jilin University, Changchun, 130012 (P. R. China)
The four compounds were synthesized in a stepwise manner
by Suzuki and Ullmann coupling reactions (see the Supporting
Information for details). The structures were fully characterized
[**] AIE=aggregation-induced emission.
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201402152.
Chem. Eur. J. 2014, 20, 7589 – 7592
7589
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