RESEARCH FRONT
Tetraphenylethene Luminogens
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internalized by the cell. Inside the cell, the aggregates can be
further processed in endosomes and lysosomes and are eventu-
ally released from the cellular organelles. The hydrophobic
nature of the aggregates prevents them from entering the
nucleus. When the nanoaggregates are bound to the biomacro-
molecules in the cytoplasm, they emit more intensely owing
to the additional physical restriction to their intramolecular
rotations.
References
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Close inspection of the cell image reveals some highly
emissive particles in the cytoplasm. These fluorescent spots
may correspond to vesicles (endosomes, lysosomes, etc.) with
large amounts of TPE nanoaggregates. To prove that the dye
aggregates enter the cell through endocytosis, we performed the
cell staining at different time intervals. The fluorescence images
were taken with an inverted fluorescence microscope to have a
better comparison of their brightness. Photographs were
obtained in black and white and pseudocoloured green, which
was the same colour emitted by 2 in the aggregate state.
The HeLa cells were first incubated with 2 for 30 min. As
shown in Fig. 5b, the nanoaggregates of 2 light up the whole
cytoplasm of the cell uniformly. Many dark spots are also
observed. The nanoaggregates of 2 may have entered the cell
membrane but not yet accumulated in the vesicles because of
insufficient incubation time. As expected, the vesicles become
emissive when the incubation time is prolonged to 3 h.
The nanoaggregates of 2 can selectively stain the cytoplasm
of the cells, endowing them with a unique advantage over
commercial CellTracker, which stains the entire cells. In most
cases, it is necessary to use two different fluorogenic dyes to
stain a cell: one to stain DNA in the nucleus, with the other to
stain the cytoplasm surrounding the nucleus. The fluorescent
dyes we developed here are therefore useful staining agents
when combined with a DNA-staining fluorogen. The nano-
aggregates of 2 can specifically accumulate in the vesicles of
the living cells, making them promising for the tracing of the
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In this work, a series of tetraphenylethene derivatives (1–4) with
variedemission colours were designed and synthesized. Whereas
they are practically non-emissive in dilute solutions, they are
induced to emit intensely by aggregate formation, demonstrating
a novel phenomenon of AIE. Restriction of intramolecular
motions is responsible for this effect. A multilayer EL device
using 2 as emitter was fabricated, which emits green light with a
maximum luminance and current efficiency of 12930 cd mꢀ2 and
3.04 cd Aꢀ1 respectively. The nanoaggregates of 1–4 are highly
emissive and cytocompatible, enabling their use for sensitive and
selective imaging the cytoplasm of living cells. Further synthesis
of red-emitting AIE luminogens and investigation of their
biological application are under way in our laboratories.
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Acknowledgement
(e) Q. Zeng, Z. Li, Y. Dong, 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.
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(f) Y. Dong, J. W. Y. Lam, A. Qin, J. Sun, J. Liu, Z. Li, J. Sun, H. H. Y.
Sung, I. D. Williams, H. S. Kwok, B. Z. Tang, Chem. Commun. 2007,
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(g) H. Tong, Y. Hong, Y. Dong, M. Haussler, J. W. Y. Lam, Z. Li,
Z. Guo, Z. Guo, B. Z. Tang, Chem. Commun. 2006, 3705. doi:10.1039/
B608425G
This work was partially supported by the Research Grants Council of Hong
Kong (Project numbers 603509, HKUST13/CRF/08 and HKUST2/CRF/10),
the Innovation and Technology Commission (ITP/008/09NP), the Univer-
sity Grants Committee of Hong Kong (AoE/P-03/08) and the National
Science Foundation of China (20974028). B.Z.T. acknowledges the support
of the Cao Guangbiao Foundation of Zhejiang University and Dr Jiaxin Sun
and Professor Hoi Sing Kwok in the Department of Electronic and Computer
Engineering in Hong Kong University of Science and Technology for the
electroluminescence measurement.