Journal of the American Chemical Society
COMMUNICATION
Scheme 2
Figure 4. (a) Transient absorption spectrum of ref-H2P (1.0 μM).
(b) Transient absorption spectra of Acr+ÀH2PÀAcr+ (1.0 μM) and
Acr•ÀH2PÀAcr• produced by the addition of KO2•ÀÀ18-crown-6
(5.0 μM) in deaerated toluene at 298 K taken 2.0 μs after laser excitation
at λex = 430 nm. (c) Decay time profiles at λ = 450 nm for 3ref-H2P* and
Acr•-3H2P*-Acr•.
In conclusion, we have developed an efficient fluorescence
•À
sensor for detection of O2 using an acridinium ion-linked
porphyrin triad (Acr+ÀH2PÀAcr+) that is responsive to elec-
tron-transfer reduction of the Acr+ moiety. The present study
provides a new strategy for fluorescence sensors that are respon-
product may be different. The spin state of Acr•ÀH2PÀAcr• istwo
independent doublets (see above), whereas the spin state of the
electron-transfer product (Acr+ÀH2P•ÀÀAcr•) is either a singlet
or a triplet because the H2P•À moiety can interact with the Acr•
moiety. Thus, electron transfer from the Acr• moiety to the 1H2P*
moiety in Acr•ÀH2PÀAcr• to produce Acr+ÀH2P•ÀÀAcr• (or
Acr•ÀH2P•ÀÀAcr+) is spin-forbidden. The endergonic electron
•À
sive to one-electron reductants such as O2
.
’ ASSOCIATED CONTENT
S
Supporting Information. Experimental procedures and
b
Figures S1ÀS5. This material is available free of charge via the
1
transfer from the Acr• moiety to the H2P* moiety is also spin-
forbidden. This may be thereason why noquenchingof 1H2P*was
observed in Acr•ÀH2PÀAcr•.
’ AUTHOR INFORMATION
The electron-transfer quenching of the fluorescence of 1H2P*
by the Acr+ moiety was also confirmed by nanosecond laser flash
photolysis measurements. No transient absorption due to the
triplet excited state of the H2P moiety was observed in Ac-
r+ÀH2PÀAcr+ because of electron transfer from 1H2P* to Acr+,
Corresponding Author
m.crossley@chem.usyd.edu.au; fukuzumi@chem.eng.osaka-u.
ac.jp
1
’ ACKNOWLEDGMENT
which is faster than the intersystem crossing from H2P* to
3H2P* (black line in Figure 4). In the case of Acr•ÀH2PÀAcr•
produced by the two-electron reduction of Acr+ÀH2PÀAcr+
with 2 equiv of KO2•ÀÀ18-crown-6, however, the transient
absorption band (λmax = 450 nm) was clearly observed, as in
the case of ref-H2P (blue line in Figure 4b vs the reference
This work at Osaka University was supported by Grants-in-
Aid (Nos. 20108010 and 23750014) and a Global COE Program,
“The Global Education and Research Center for Bio-Environ-
mental Chemistry” from the Ministry of Education, Culture,
Sports, Science and Technology, Japan, and by KOSEF/MEST
through WCU Project R31-2008-000-10010-0, Korea. We also
thank the Australian Research Council for partial funding of this
research (Grant DP1092560).
3
spectrum in Figure 4a). The triplet lifetime of Acr•À H2P*ÀAcr•
is shorter than that of ref-H2P (Figure 4c), probably because of
3
electron transfer from the Acr• moiety to the H2P* moiety
followed by fast back electron transfer.
The energy diagrams for the photodynamics of Acr+ÀH2PÀ
Acr+ and Acr•ÀH2PÀAcr• are summarized in Scheme 2. The
singlet excited state (1H2P*) produced upon photoexcitation of
Acr+ÀH2PÀAcr+ is quenched by spin-allowed electron transfer
’ REFERENCES
(1) (a) de Silva, A. P.; Gunaratne, H. Q. N.; Gunnlaugsson, T.;
Huxley, A. J. M.; McCoy, C. P.; Rademacher, J. T.; Rice, T. E. Chem. Rev.
1997, 97, 1515. (b) Jiang, P.; Guo, Z. Coord. Chem. Rev. 2004, 248, 205.
(c) Que, E. L.; Domaille, D. W.; Chang, C. J. Chem. Rev. 2008, 108, 1517.
(d) Domaille, D. W.; Que, E. L.; Chang, C. J. Nat. Chem. Biol. 2008,
4, 168.
1
from the H2P* moiety to the Acr+ moiety followed by fast back
electron transfer. from the Acr• moiety to the H2P•+ moiety, and
therefore, it exhibits little fluorescence. Once the two Acr+ moieties
are reduced by O2 to produce Acr•ÀH2PÀAcr•, the H2P*
moiety is not quenched in toluene by either endergonic electron
transfer from the 1H2P* moiety to the Acr• moiety or spin-forbidden
electron transfer from the Acr• moiety to the 1H2P* moiety, so it
exhibits much stronger fluorescence than Acr+ÀH2PÀAcr+.
In a polar solvent such as MeCN, the formation of Ac-
r•ÀH2PÀAcr• was also confirmed by EPR measurements
(Figure S5 in the SI). In sharp contrast to the case in toluene,
no fluorescence from the singlet excited state in Acr•ÀH2PÀAcr•
(2) (a) Schmidtchen, F. P.; Berger, M. Chem. Rev. 1997, 97, 1609.
•À
1
(b) Beer, P. D.; Gale, P. A. Angew. Chem., Int. Ed. 2001, 40, 486.
ꢀ
(c) Sessler, J. L.; Davis, J. M. Acc. Chem. Res. 2001, 34, 989. (d) Martinez-
Mꢀanez, R; Sancenꢀon, F. Chem. Rev. 2003, 103, 4419.
(3) (a) Winterbourn, C. C. Nat. Chem. Biol. 2008, 4, 278.
(b) Gomes, A.; Fernandes, E.; Lima, J. L. F. C. J. Biochem. Biophys.
Methods 2005, 65, 45. (c) Degli Esposti, M. Methods 2002, 26, 335.
(4) Rurack, K.; Resch-Genger, U. Chem. Soc. Rev. 2002, 31, 116.
(5) (a) Corneillie, T. M.; Whetstone, P. A.; Fisher, A. J.; Meares,
C. F. J. Am. Chem. Soc. 2003, 125, 3436. (b) Yuasa, J.; Fukuzumi, S. J. Am.
Chem. Soc. 2008, 130, 566. (c) Ojida, A.; Takashima, I.; Kohira, T.;
Nonaka, H.; Hamachi, I. J. Am. Chem. Soc. 2008, 130, 12095.
(Acr•À H2P*ÀAcr•) was observed in MeCN because of fast
1
electron transfer from the Acr• moiety to the 1H2P* moiety.15
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dx.doi.org/10.1021/ja204161j |J. Am. Chem. Soc. 2011, 133, 11092–11095