TFA/chloroform, methanol, ethanol, or acetone mixtures,
ABPX01+ were well dispersed and displayed AIEE. The
emission spectrum of 500 mM of ABPX01+ in THF was
nonemissive. In contrast, ABPX02+–04+ similarly showed
AIEE and a slightly continuous red shift was observed with
an increase in the N,N0-dialkyl chain length (Fig. S9, ESIw).
Marked aggregation and enhanced emission were observed in
ABPX+ as the N-alkyl chain length was increased. These
results suggested that ABPX+ exhibited unique AIEE and
the AIEE of ABPX+ was driven by hydrophobic forces.
ABPX+ showed long-wavelength emission over the near-
infrared region compared with representative AIEE-active
silole, anthracene, and other derivatives.7,8 The emission
spectra by a conventional photometric method showed a
random shift of the maximum wavelength, which was caused
by the internal shielding effect when ABPX01+ was measured
at a high concentration. The problem was solved by using the
surface photometric method (Fig. S10, ESIw).
In conclusion, we have succeeded in synthesizing a new class
of rhodamine luminophores (ABPX). ABPX have been
feasibly synthesized by the condensation of individual
benzophenone derivative with resorcinol. The emission
behavior of ABPX was directly opposite to the concentration
quenching of conventional rhodamine dyes. These results
indicated that ABPX exhibited unique AIEE. Now, we are
currently devoting our effort to the investigation of the
structure–AIEE relationships to prove the design concepts.
The success of ABPX series is expected to accelerate organic
photomaterial discovery and lead to further technological
applications in the fields of nanobiotechnology, photonics, and
optoelectronics, and potential uses in photodynamic therapy.
The authors would like to express their sincere gratitude to
The High Technology Research of Japan. This research was
supported by the Kyoto-Advanced Nanotechnology Network.
We would also like to thank Ms Mihoyo Fujitake for MS
measurement; Prof. Dr Yuji Kobayashi, Masaki Mifune,
Hiroki Kakuta and Isao Takahashi, Messrs Takahiro
Maruno and Sadaharu Maeda, and Ms Keiko Watanabe for
helpful discussion. We also thank Otsuka Electronics, Co.,
Ltd. for the dynamic laser scattering measurement.
The aggregation phenomena of ABPX01+ were confirmed
by spectrophotometric analysis. Level-off tails in the visible
region of the absorption spectra in methanol or water/THF
mixtures clearly suggested the formation of suspended
particles owing to the Mie scattering effect (Fig. S11(a),
ESIw). The tails in chloroform could not be observed
although AIEE was the most active in this case. The result
indicated that the particle size of ABPX01+ might be different
in response to solvent changes.
Notes and references
1 (a) M. Sameiro and T. Goncalves, Chem. Rev., 2009, 109, 190;
(b) M. C. Gutierrez, M. J. Hortiguela, M. L. Ferrer and F. del
Monte, Langmuir, 2007, 23, 2175; (c) F. Stracke, M. Heupel and
E. Thiel, J. Photochem. Photobiol., A, 1999, 126, 51.
We used dynamic laser scattering (DLS) to elucidate the
particle size of ABPX01+ in 90% water/THF mixtures
(containing 1% TFA) at 25 1C. Fig. S11(b), ESIw shows the
time dependence of the particle size distribution of 500 mM
of ABPX01+. The particle size of ABPX01+ aggregates was
500 nm immediately after the preparation of ABPX01+.
The ABPX01+ aggregates then grew to a size of more than
1200 nm after 30 min. The particle size of ABPX01+ in
methanol and chloroform (respectively, containing 1% TFA)
could not be calculated because the fluctuation of the scattered
photons was not sufficiently observed owing to the
subnanometre size. These results indicated that the particle
size might be dependent on the dispersion of ABPX01+ in
various solvents. In order to further visualize the aggregates
with emission measurements, aggregates of ABPX01+ in 90%
water/THF mixtures (containing 1% TFA) were collected after
30 min using a membrane of 500 nm pore size and emission was
noted under 365 nm irradiation (Fig. S12, ESIw). Evidence
showing that ABPX+ possess the property of AIEE can be
found in the above-mentioned results.
2 (a) L. Antonov, G. Gergov, V. Petrov, M. Kubista and J. Nygren,
Talanta, 1999, 49, 99; (b) K. Igarashi, M. Maeda, T. Takao, Y. Oki
and H. Kusama, Bull. Chem. Soc. Jpn., 1999, 72, 1197;
(c) O. Valdes-Aguilera and D. C. Neckers, Acc. Chem. Res.,
1989, 22, 171; (d) M. Faraggi, P. Peretz, I. Rosenthal and
D. Weinraub, Chem. Phys. Lett., 1984, 103, 310.
3 J. Bujdak and N. Iyi, J. Phys. Chem. B, 2006, 110, 2180.
4 (a) R. Sasai, N. Iyi, T. Fujita, F. L. Arbeloa, V. M. Martinez,
K. Takagi and H. Itoh, Langmuir, 2004, 20, 4715; (b) S. Dare-
Doyen, D. Doizi, P. Guilbaud, F. Djedaini-Pilard, B. Perly and
P. Millie, J. Phys. Chem. B, 2003, 107, 13803.
5 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.
6 (a) Z. J. Zhao, S. M. Chen, X. Y. Shen, F. Mahtab, Y. Yu, P. Lu, J.
W. Y. Lam, H. S. Kwok and B. Z. Tang, Chem. Commun., 2010, 46,
686; (b) J. W. Chung, S. J. Yoon, S. J. Lim, B. K. An and
S. Y. Park, Angew. Chem., Int. Ed., 2009, 48, 7030;
(c) W. X. Tang, Y. Xiang and A. J. Tong, J. Org. Chem., 2009,
74, 2163; (d) 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; (e) M. Shimizu, H. Tatsumi,
K. Mochida, K. Shimono and T. Hiyama, Chem.–Asian J., 2009, 4,
1289.
7 Y. N. Hong, J. W. Y. Lam and B. Z. Tang, Chem. Commun., 2009,
4332.
In order to check whether or not RIR is involved in AIEE of
ABPX01+, we studied viscochromism and thermochromism
of the ABPX01+ emission. RIR was affected by the viscosity
and temperature of the solvent. As the viscosity of the solvent
(glycerol/methanol) increased or the temperature of methanol
decreased, the emission exhibited by ABPX01+ increased (Fig.
S13, ESIw). ABPX01+ inhibited intramolecular rotation and
induced AIEE at high viscosity and low temperature. These
results indicate that RIR in ABPX01+ plays a crucial role in
the emission enhancement in the aggregates states.
8 (a) J. T. He, B. Xu, F. P. Chen, H. J. Xia, K. P. Li, L. Ye and
W. J. Tian, J. Phys. Chem. C, 2009, 113, 9892; (b) S. Kim, Q. Zheng,
G. S. He, D. J. Bharali, H. E. Pudavar, A. Baev and P. N. Prasad,
Adv. Funct. Mater., 2006, 16, 2317.
9 S. Kamino, H. Ichikawa, S. I. Wada, Y. Horio, Y. Usami,
T. Yamaguchi, T. Koda, A. Harada, K. Shimanuki, M. Arimoto,
M. Doi and Y. Fujita, Bioorg. Med. Chem. Lett., 2008, 18, 4380.
10 T. Nguyen and M. B. Francis, Org. Lett., 2003, 5, 3245.
11 N. O. McHedlov-Petrossyan, N. A. Vodolazkaya and
A. O. Doroshenko, J. Fluoresc., 2003, 13, 235.
12 B. K. An, S. K. Kwon, S.-D. Jung and S. Y. Park, J. Am. Chem.
Soc., 2002, 124, 14410.
c
This journal is The Royal Society of Chemistry 2010
Chem. Commun., 2010, 46, 9013–9015 9015