麻烦翻译下Figure 1 displays the emission spectra

麻烦翻译下Figure 1 displays the emission spectra
Figure 1 displays the emission spectra changes of QB upon
the addition of an increasing amount of Zn2+ and Cd2+. Free
QB showed weak fluorescence emission at 405 nm upon
excitation at 295 nm (ε ) 0.87 × 104 M-1 cm-1, Φ0 ) 0.057)
in buffer solution because of the efficient PET quenching
from the DPA moiety to the quinoline fluorophore. Remarkable
fluorescence enhancements were detected upon the
addition of Zn2+ and Cd2+, respectively. Upon binding Zn2+,
QB showed a larger emission red-shift of 53 nm from 405
to 458 nm with an isoemissive point at 400 nm (Figure 1a),
indicating that a promoted ICT process occurred with
consequent ratiometric fluorescent signals. The ratio of
emission intensities (F458 nm/F380 nm) varies from 0.6 to 12
and is saturated up to a molar ratio (QB/Zn2+) of 1:1 (Figure
1b). In contrast, upon binding Cd2+, only enhanced fluorescent
intensity (ΦCd ) 0.22) with a smaller wavelength shift
(20 nm), but without an isoemissive point, were observed
(Figure 1c), suggesting that sensor QB recognizes Cd2+
principally based on the CHEF mechanism. The titration
curves as shown in Figure 1b,d demonstrate the high binding
affinities12 and 1:1 complexes between Zn2+, Cd2+, and QB.
To obtain an insight into the sensing properties of QB
toward metal ions, we investigated the fluorescence titration
of different ions in CH3CN/H2O buffer solution (Figure 2).
Quenching effects were observed when heavy metal ions of
Co2+, Ni2+, Cu2+, Hg2+, and Pb2+ were added, as observed
in other quinoline-DPA-based sensors. Addition of Mg2+,
Ca2+, and Na+ exerted no or little effect on the emission of
QB, even at high concentration (1 mM). As expected,
remarkable fluorescence changes were detected upon the
addition of either Zn2+ or Cd2+. The Zn2+-selective ratiometric
response (F458nm/F380nm up to 12) of QB was clearly
observed (Figure 2b) and was not interfered by the presence
of Mn2+, Fe3+, Mg2+, Ca2+, K+, and Na+ (Figures S4 and
S5, Supporting Information). Considering the distinct fluorescent
enhancement upon binding Cd2+, QB can also be
used as a CHEF Cd2+-selective sensor. In this case, other
metals behave similarly as in the case of Zn2+ (Figure S3,
Supporting Information). These results suggest that QB had
good selectivity for Zn2+ and Cd2+