The luminescence responses of Pt-1 and Pt-2 toward varia-
tion of O concentration were studied (Fig. 4). For Pt-1, with
Notes and references
2
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increase in the O concentration, the emission at 683 nm was
2
quenched, and this emission band disappeared completely at
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5
0% O (v/v, mixture with N ). Interestingly, the fluorescence
2 2
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band at 502 nm is intact. This is consistent with the fluores-
cence feature of this emission band and indicates that there is
no significant equilibrium between the triplet emissive state
and the singlet emissive state, which is in agreement with the
6
7
7
7 K emission spectra (see ESIw).
It should be pointed out that the fluorescence/phosphores-
cence bands of Pt-1 or Pt-2 are well-separated, the energy gaps of
8 E. J. Park, K. R. Reid, W. Tang, R. T. Kennedy and R. Kopelman,
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À1
À1
the singlet and triplet emission are 5279 cm and 4743 cm for
Pt-1 and Pt-2, respectively. Previously a complex was used for
ratiometric O sensing, i.e. [(dppe)Pt{S C (CH CH -N-2-pyridi-
9
P. J. Cywinski, A. J. Moro, S. E. Stanca, C. Biskup and
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14c,19b
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nium)}][BPh ] (dppe = 1,2-bis(diphenylphosphino)ethane],
4
1
1
1
1
1 R. C. Evans, P. Douglas, J. A. Gareth Williams and
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which shows less separated fluorescence/phosphorescence bands
À1
(energy gap of the two emission bands is 2838 cm ). A large
separation between the fluorescence/phosphorescence bands of
Pt-1 or Pt-2 is beneficial for ratiometric sensing.
2
006, 45, 10922.
The quenching of phosphorescence of Pt-1 and Pt-2 can be
quantitatively studied by Stern–Volmer equation (Fig. 4c), with
the ratiometric response (intensity ratio at 503 nm and 683 nm).
4 (a) C. Qin, W.-Y. Wong and L. Wang, Macromolecules, 2011,
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Good linearity was found in the range of 0.0%–20% bar of O
À1
2
.
The fitting results give a KSV value of 45.1 Æ 1.4 bar , which is
much higher than that for a recent ratiometric O sensor based
2
15 G. Zhang, J. Chen, S. J. Payne, S. E. Kooi, J. N. Demas and
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16 G. Q. Zhang, G. M. Palmer, M. W. Dewhirst and C. S. Fraser,
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À1
7
on quantum dots and pyrene (0.4 bar ). Pt-2 shows higher
À1
sensitivity (136.0 Æ 3.7 bar ), due to its longer phosphorescence
11,30–33
lifetime (3.75 ms).
1
1
1
7 J. Hu, J. H. K. Yip, D. L. Ma, K. Y. Wong and W. H. Chung,
We investigated the luminescence lifetime variation in O
sensing (Fig. 4d). Phosphorescence lifetimes decrease sharply
at higher O concentration, for example, the phosphorescence
lifetime of Pt-2 changed from 3.75 ms to 0.46 ms by changing
from 0.0 to 0.1 bar O , but the lifetimes of fluorescence do not
change (see ESIw). Thus multi-mode ratiometric (intensity and
2
Organometallics, 2009, 28, 51.
8 H. Hochreiner, I. Sanchez-Barragan, J. M. Costa-Fernandez and
´ ´ ´
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2
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0 (a) H. J. Kim, S. Y. Park, S. Yoon and J. S. Kim, Tetrahedron,
2
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lifetime) O sensing with Pt-1 and Pt-2 is feasible. Furthermore,
2
we demonstrated that the O sensing dynamic range can be easily
2
2
1 D. N. Kozhevnikov, V. N. Kozhevnikov, M. M. Ustinova,
A. Santoro, D. W. Bruce, B. Koenig, R. Czerwieniec, T. Fischer,
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tuned by changing the phosphorescence lifetime of the complexes.
This is feasible since the lifetime can be tuned by changing the
structure of the C^N ligands.
2
In summary, we have prepared cyclometalated C^N Pt(II)
acac complexes that show balanced fluorescence and phos-
phorescence dual emission at room temperature, the singlet
and triplet features of the two emission bands were proved by
luminescence lifetimes, emission spectra at 77 K, as well as
2
009, 19, 4457; (c) G. Zhou, Q. Wang, X. Wang, C.-L. Ho,
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2
2
4 G. Zhou, Q. Wang, W.-Y. Wong, D. Ma, L. Wang and Z. Lin,
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2
sensitivity to O . We found that the phosphorescence band of
the complexes can be significantly quenched by O , whereas the
2
25 J. Brooks, Y. Babayan, S. Lamansky, P. I. Djurovich, I. Tsyba,
R. Bau and M. E. Thompson, Inorg. Chem., 2002, 41, 3055.
fluorescence bands are intact. The O sensing can be monitored
2
2
2
6 Q. Zhao, F. Li and C. Huang, Chem. Soc. Rev., 2010, 39, 3007.
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by both intensity and lifetime modes. Furthermore, the O2
sensing dynamic range can be readily tuned by changing the
phosphorescence lifetime of the complexes. Our work will be
2
2
useful for ratiometric O sensing with uni-luminophore molecules
2
3
that show fluorescence–phosphorescence dual emission.
We thank the NSFC (20972024 and 21073028), Royal
Society (UK) and NSFC (China–UK Cost-Share program,
31 W. Wu, W. Wu, S. Ji, H. Guo, P. Song, K. Han, L. Chi, J. Shao
and J. Zhang, J. Mater. Chem., 2010, 20, 9775.
3
2
1011130154), Fundamental Research Funds for the Central
2 H. Guo, S. Ji, W. Wu, W. Wu, J. Shao and J. Zhao, Analyst, 2010,
35, 2832.
Universities (DUT10ZD212 and DUT11LK19) and Ministry
of Education (SRFDP-200801410004 and NCET-08-0077) for
financial support.
1
3 W. Wu, W. Wu, S. Ji, H. Guo and J. Zhao, Dalton Trans., 2011,
5953.
3
This journal is c The Royal Society of Chemistry 2011
Chem. Commun., 2011, 47, 11471–11473 11473