S. Li et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 137 (2015) 581–588
583
3.22–3.26 (q, 4H, NCH2CH3), 5.32 (s, NHCH2CH3), 6.03 (s, 1H,
ArAH), 6.11 (d, 1H, ArAH), 6.17 (s, 2H, xanthene-H), 6.44 (s, 2H,
xanthene-H), 7.17 (dd, 1H, ArAH), 7.32 (d, 1H, ArAH), 7.58 (dd,
2H, ArAH), 8.26 (dd, 1H, ArAH), 8.41 (s, 1H, CH@N), 9.12 (s,
ArAOH). 13C NMR (CDCl3), d (ppm): 13.33, 14.49, 16.86, 35.24,
46.37, 75.87, 98.32, 99.94, 103.37, 106.39, 113.45, 118.35, 127.39,
127.78, 129.01, 129.64, 131.54, 132.74, 132.80, 138.87, 143.26,
143.35, 148.69, 153.34, 164.32, 171.12. MS m/z: [m + 1]+ calc. for
photophysical measurements were recorded using sample suspen-
sions in NaAc–HAc buffer (pH = 7)/CH3CN (V:V = 1:1). A tunable
laser was used as the excitation source (Continuum Sunlite OPO)
(k = 980 nm).
Results and discussion
Characterization on up-conversion host
C
37H41N5O3, 603.8; found, 604.8. Melting point: 212–215 °C.
2-((4-(diethylamino)-2-hydroxybenzylidene) amino)-30,60-bis
To minimize background light interference and probe photoble-
aching, an up-conversion host is selected as the excitation source,
as above mentioned. NaYF4 lattice has been proved as a promising
one owing to its high up-conversion efficiency [11]. During host
preparation procedure, to allow a fast growth along [001] crystal-
lographic direction and obtain hexagonal prism-liked crystals, con-
centrated rare earth and NaF solutions were used to facilitate the
dissolution–reconstruction process, where oleic acid served as a
stabilizing reagent. Considering that the resulting nanocrystals
were covered by hydrophobic oleic acid chains, they were later
treated by an amphiphilic surfactant of Triton X-100 so that the
crystals became hydrophilic and dispersible in aqueous solutions.
A hexagonal prism-liked morphology with mean diameter of
20 nm can be identified by the SEM and TEM images of the nano-
crystals (Triton X-100 processed), as shown in Fig. S1 (see Support-
ing information). Their composition can be firstly revealed by the
EDX data shown in Fig. 1. There are C, F, Na, Er, Yb and Y elements
in the nanocrystals, which is consistent with our proposed compo-
sition. The existence of C element suggests that there may be some
remaining X-100 or oleic acid attached to the nanocrystals. As
shown in Fig. 2, the powder XRD pattern of the nanocrystals (Triton
X-100 processed) is nearly identical to that of pure hexagonal
NaYF4 nanocrystals (JCPDS card No. 28-1192). There can be found
no other diffraction peaks, suggesting that the NaYF4 lattice has
been preserved well after the incorporation of Yb(III) and Er(III)
ions. Considering above results, it can be concluded that the up-
conversion host b-NaYF4:Yb3+/Er3+ has been successfully
constructed.
(ethylamino)-20,70-dimethylspiro[isoindoline-1,90-xanthene]-3-thi-
one (denoted as 5).
5 was synthesized following a similar
procedure for 4, except that 2 was replaced by 3. 1H NMR (CDCl3),
d (ppm): 1.15–1.19 (t, 6H, NCH2CH3), 1.28–1.33 (t, 6H, NCH2CH3),
1.93 (s, 6H, xanthene-CH3), 3.11–3.16 (q, 4H, NCH2CH3), 3.20–
3.25 (q, 4H, NCH2CH3), 5.32 (s, NHCH2CH3), 6.05 (s, 1H, ArAH),
6.13 (d, 1H, ArAH), 6.19 (s, 2H, xanthene-H), 6.45 (s, 2H, xan-
thene-H), 7.18 (dd, 1H, ArAH), 7.31 (d, 1H, ArAH), 7.59 (dd, 2H,
ArAH), 8.27 (dd, 1H, ArAH), 8.44 (s, 1H, CH@N), 9.14 (s, ArAOH).
13C NMR (CDCl3), d (ppm): 13.78, 14.61, 16.93, 36.12, 46.52,
79.95, 98.14, 99.18, 104.65, 106.62, 113.27, 118.47, 124.67,
126.32, 129.78, 130.25, 131.17, 132.84, 141.56, 141.69, 143.12,
143.31, 148.79, 153.41, 161.92, 169.31. MS m/z: [m + 1]+ calc. for
C37H41N5O2S, 619.8; found, 620.8. Melting point: 216–219 °C.
Up-conversion host
The up-conversion host b-NaYF4:Yb3+/Er3+ was synthesized by
the following procedure [8]. The solution of NaOH (17 mmol),
NaF solution (0.8 M, 10 mL), oleic acid (7 g) and ethanol (12 mL)
was stirred and aged at room temperature for 30 min. After the
addition of Yb(NO3)3 solution (0.2 M, 1 mL), Y(NO3)3 solution
(0.4 M, 2 mL) and Er(NO3)3 solution (0.01 M, 2 mL), the mixture
was held still for 30 min and then sealed into a Teflon bottle. The
mixture was heated to 200 °C and kept for 10 h (heating
rate = 10 °C/min). After being cooled naturally, the solid product
was collected and dispersed in Triton X-100 (30 mL). The mixture
was processed with ultrasonic bath for 20 min. The solid product
was collected by centrifugation, washed and dried to give the up-
conversion host b-NaYF4:Yb3+/Er3+
.
Photophysical measurement on the host and the two chemosensors
Emission and absorption spectra
Sensing system
Since b-NaYF4:Yb3+/Er3+ nanocrystals are designed as the excita-
tion host, the possibility of energy transfer between b-NaYF4:Yb3+
/
A typical sensing system was constructed as follows. A con-
trolled amount of b-NaYF4:Yb3+/Er3+ was added into 1 L of NaAc–
HAc buffer solution (pH = 7)/CH3CN (V:V = 1:1) to form a 5 wt%
solution. Then chemosensor (0.01 mmol) was added. The solution
was treated with ultrasonic bath for 10 min for further
measurements.
Er3+ and the two chemosensors should be considered. First, their
absorption and emission spectra are shown in Fig. 3 for comparison.
The up-conversion host owns three major bands peaking at 522 nm,
541 nm and 653 nm, respectively. Those bands can be assigned to
Equipments
The equipments and measuring methods used in this work are
listed as follows. NMR and mass spectra were taken by a Varian
INOVA 300 spectrometer and a Agilent 1100 MS spectrometer
(COMPACT), respectively. Melting point measurement as finished
on a MPA100 (SRS) melting-pint apparatus. Scanning and trans-
mission electron microscopy (SEM and TEM) images were shot
by a Hitachi S-4800 microscope and a JEM-2010 transmission elec-
tion microscope (Japanese JEOL Company), respectively. Energy-
dispersive X-ray (EDX) data were taken simultaneously by the
JEM-2010. UV–Vis absorption and fluorescence emission spectra
were recorded by a Hitachi UV-3110PC UV–VIS-NIR scanning spec-
trophotometer and a Hitachi F-4500 fluorescence spectrophotom-
eter, respectively. The excited state lifetimes were recorded by a
two-channel
TEKTRONIX
TDS-3052
oscilloscope.
Above
Fig. 1. The EDX data of the host nanocrystals (Triton X-100 processed).