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X. Zhang, Y. Chen / Journal of Photochemistry and Photobiology A: Chemistry 335 (2017) 119–123
powder. (b) To the solution of 8-formyl-7-hydroxy-4-methylcou-
marin (102 mg, 0.5 mmol) in ethanol absolute (10 ml) was added 2-
aminobenzothiol (69 mg, 0.55 mmol). The solution mixture was
stirred at ambient temperature for 3 h till the starting material was
disappeared. A colourless solid was produced. The crude product
was washed with EtOH (5 ml  3) and petroleum ether (5 ml  3),
respectively, to afford ligand 1 (140 mg, 90%) without further
purification. (c) Zinc acetate dihydrate (44 mg, 0.2 mmol) was
dissolved in methanol (5 ml). After zinc acetate dihydrate was
dissolved completely in methanl, to the solution was added ligand
1 (62 mg, 0.2 mmol). The mixture solution was stirred at ambient
temperature for 2 h till the starting material was disappeared. A
yellow solid was produced. The crude product was washed with
ether (5 ml  2) and methanol (5 ml  2), respectively, and pure
complex 2 (70 mg, 90%) was obtained after vacuum-dried without
Scheme 1. Outline of photo-release of Zn2+ in solution.
reference. HRMS spectra were recorded with GC-TOF MS
spectrometer (Thermo Fisher, Q-Exactive MS). UV absorption
spectra and fluorescence spectra were measured with an absorp-
tion spectrophotometer (Hitachi U-3010) and a fluorescence
spectrophotometer (Hitachi F-2500), respectively. Transient ab-
sorption spectrum was measured by nanosecond laser flash
photolysis spectrometer (LF900) with a Nd: YAG laser (Continuum,
Surelite I-10, 4–6 ns fwhm) with a power of 10–15 mJ/pulse. The
photochemical reactions were monitored by continuous exposure
to a Xe-920 lamp (150 W) as a probe light and a photomultiplier
tube (Hamamatsu R 928) as a detector. All chemicals for synthesis
were purchased from commercial suppliers, and solvents were
purified according to standard procedures. Reaction monitored by
TLC silica gel plates (60F-254). Column chromatography was
performed on silica gel (Merck, 70–230 mesh). A 365 nm lamp
(36 W) was used as light sources for photo-triggered release. A high
pressure Hg lamp (500 W) was used as light source for the
preparation of sample 3.
further purification. M.p. >300 ꢀC. 1H NMR (400 MHz, DMSO-d6):
d
(ppm) 9.17 (s,1H), 7.58 (d, J = 9.2 Hz,1H), 7.39 (dd, J = 6.1, 3.1 Hz,1H),
7.33 (dd, J = 6.1, 3.2 Hz, 1H), 6.98 (d, J = 6.0 Hz, 2H), 6.65 (d, J = 9.1 Hz,
1H), 6.01 (s, 1H), 2.37 (s, 3H). 13C NMR (100 MHz, DMSO):
d (ppm)
173.23,159.96,156.54,154.40,153.87,145.25,144.00,132.21,129.14,
126.62, 122.15, 120.09, 116.00, 107.49, 106.79, 106.62, 18.45. HRMS
(m/z) calcd for C17H13NO4SZn (M+ÀH2O): 372.9751. Found:
372.9756 (100%). Anal. Calcd for C17H13NO4SZn: C, 51.99; H,
3.34. Found: C, 52.14; H, 3.29.
Sample 3, which is prepared for control experiment, was
obtained from the photo-conversion of ligand 1 (Scheme 3). 1
(311 mg, 1.0 mmol) was dissolved in DMSO (10 ml), the solution
was stirred at ambient temperature with the light irradiation (high
pressure mercury lamp, exposure 39.5 mW/cm2) till no starting
material was detected by TLC plate. After evaporation of the
solvent, the crude product was purified by flash column
chromatography (petroleum ether/ethyl acetate = 2: 1, v/v) to
afford sample 3 (224 mg, 72%). M.p. = 242–243 ꢀC (Ref. [25]: 241–
2.2. Chemical
242 ꢀC). 1H NMR (400 MHz, CDCl3):
J = 15.4, 8.0 Hz, 2H), 7.48 (d, J = 8.7, 1H), 7.46 (t, J = 7.8 Hz, 1H), 7.37 (t,
J = 7.3 Hz, 1H), 6.93 (d, J = 8.9 Hz, 1H), 6.07 (s, 1H), 2.34 (s, 3H). 13
NMR (100 MHz, CDCl3): (ppm) 162.29, 161.72, 158.52, 152.26,
d (ppm) 14.66 (s, 1H), 7.91 (dd,
Complex 2 was prepared according to the literature [24] using
the synthetic routes described in Scheme 2. The detailed procedure
for preparation is presented as follows: (a) 7-hydroxy-4-methyl-
coumarin (5.28 g, 30 mmol) and hexamine (9.8 g, 70 mmol) in
glacial acetic acid (50 ml) were heated for 6 h at 95 ꢀC. Then 20%
HCl (75 ml, conc. HCl/H2O = 84/100, v/v) was added in and the
mixture was further hearted for 30 min at 70 ꢀC, after which the
mixture was cooled and extracted with ether twice (50 ml  2). The
combined organic layer was concentrated under reduced pressure,
and pure 8-formyl-7-hydroxy-4-methylcoumarin (612 mg, 10%)
was obtained by recrystallization from ethanol as light yellow
C
d
151.28, 147.78, 132.64, 126.60, 125.73, 124.67, 120.6493, 120.4589,
113.61, 110.64, 109.81, 104.70, 18.06. TOF-MS (EI) calcd for
C
17H11NO3S (M+): 309.0460. Found: 309.0468 (100%). Anal. Calcd
for C17H11NO3S: C, 66.01; H, 3.58. Found: C, 66.06; H, 3.54.
3. Results and discussion
3.1. Absorption and fluorescence of complex 2
Dilute solution of 2 (20
was prepared by the addition of 20
m
M) in phosphate buffer (PBS, pH = 7.2)
l of 2 in DMSO (2 mM) to 2 ml
m
of Tween-20 (10 mM) in PBS buffer. Absorption and fluorescence of
2 in micelle solution are presented in Fig. 1. It was found that the
absorption maximum of 2 in aqueous Tween-20 solution was
around at 315 nm (
420 nm. Upon excitation with 320 nm light, a blue fluorescence
e
= 1.75 Â104 l molÀ1 cmÀ1) with a shoulder at
Scheme 2. Synthesis of complex 2. Reagents and conditions: (a) hexamine, glacial
acetic acid, 95 ꢀC, 6 h, 10%; (b) 2-aminobenzothiol, dry ethanol, rt, 3 h, 90%; (c) Zinc
acetate dehydrate, methanol, rt, 2 h, 90%.
Scheme 3. Synthesis of sample 3.