Supplementary data
Photophysical properties and pH sensing applications of luminescent
salicylaldehyde derivatives
Jiaoyan Liu, Jinghui Cheng, Xiaofeng Ma, Xiangge Zhou, and Haifeng Xiang*
College of Chemistry, Sichuan University, Chengdu, 610041, China
1
Experimental
Materials and instrumentation
All reagents were purchased from commercial suppliers and used without further purification.
UV/visible absorption spectra were recorded using a UV 765 spectrophotometer with quartz
cuvettes of 1 cm pathlength. Fluorescence spectra were obtained using an F-7000 Fluorescence
spectrophotometer (Hitachi) at room temperature. The slit width was 2.5 or 5.0 nm for both
excitation and emission. The photon multiplier voltage was 400 V. Salicylic acid, 2chlorophenol, 2-nitrophenol, Sal, 3-NO2, 3-F, 3-OMe, 4-OMe, 4-NEt2, 5-OMe, 3-Me, 3-Bu, 3Cl, and Naph were purchased from J&K Chemical Company. 5-CO2H was prepared according
to the previous report [37]. All the 5-sulfosalicylaldehyde molecules were prepared according to
our previous report [12].
Synthesis
5-carboxyl-2-hydroxybenzaldehyde (5-COOH) [34]: 4-Hydroxybenzoic acid (15.0 g; 108 mmol) was
suspended in 40 mL of trifluoroacetic acid under nitrogen. A solution of hexamethylenetetramine (15.3
g, 109 mmol) in 45 mL of trifluoroacetic acid was added dropwise. The resulting mixture was refluxed
under nitrogen and monitored by thin-layer chromatography (10 CHCl3 +1.5 CH3OH). The reflux was
maintained until the disappearance of the 4-hydroxybenzoic acid (ca. 2 h). After cooling to room
temperature, the mixture was added to 300 mL 4 mol L1 HCl and stirred for 3 h. The yellow precipitate
was then isolated by filtration and abundantly washed with water. The yellow solid was dried under
vacuum (40 % yield); 1H NMR (DMSO-D6, 400 MHz): δ (ppm) 10.15 (s, 1H), 8.44 (d, 1H), 8.20 (dd,
1H), 7.06 (d, 1H). Calcd (found): C, 57.84 (57.56); H, 3.64 (3.34). ESI-MS: m/z 166.
salicylaldehyde-5-sulfonate sodium (5-S) [12]: The compound salicylaldehyde (6.10 g, 0.05mol) was
poured in a 250 mL round-bottomed flask containing 100 mL ethanol. To the reaction mixture, the
ethanol solution (10 mL) of aniline (4.65 g, 0.05 mol) was added and the mixture was stirred at 80 ◦C for
2 h. After cooling, the solvent was evaporated to give pale yellow liquid N-phenyl-salicylaldimine.
Yield: 9.65 g (98 %); Then concentrated sulphuric acid (30 mL, 98 wt %, δ = 1.84 g/mL) was added
slowly into the above liquid by dropping funnel, and the mixture was stirred at 105℃ for 2 h. After
cooling, the solution was added slowly to ice water with vigorous stirring and a bright yellow solid
precipitated, filtered and washed with cold water. Then the solid was dissolved completely in hot water
and was allowed to cool. The yellow N-phenyl-5-sulfonato-salicylaldimine was filtered off, washed
2
with ethanol, and dried under vacuum. Yield: 8.0 g (60 %); N-Phenyl-5-sulfonato-salicylaldimine (6.0 g,
21.7 mmol) and Na2CO3 (3.2 g, 30.2mmol) were boiled vigorously in an open flask containing 35 mL
distilled water for 2 hours. Glacial acetic acid was then added to the cooled solution to pH=5 followed
by ethanol (50 mL). The mixture was cooled to 0 ℃, the beige white solid salicylaldehyde-5-sulfonate
sodium was filtered off, washed with ethanol, and dried under vacuum. Yield: 5.0 g (83%); 1H NMR
(D2O, 400 MHz): δ (ppm) 9.93 (d, 1H), 8.08 (t, 1H), 7.937.96 (m, 1H), 7.05 (s, 1H). Anal. Calcd
(found): C, 37.51 (37.46); H, 2.25 (2.30); S, 14.30 (14.27). ESI-MS: m/z = 201.
3-methyl-salicylaldehyde-5-sulfonate sodium (5-S-3-Me) [12]: 5-S-3-Me was prepared by a similar
procedure as that used for 5-S, but with 3-methylsalicylaldehyde (6.8 g, 0.05 mol) to give pale grey
solid (82 % yield); 1H NMR (D2O, 400 MHz): δ (ppm) 9.849.87 (m, 1H), 7.767.79 (m, 2H),
2.112.13 (m, 3H). Anal. Calcd (found): C, 40.34 (40.26); H, 2.96 (2.31); S, 13.46 (13.37). ESI-MS:
m/z = 215.
3-tertbutyl-salicylaldehyde-5-sulfonate sodium (5-S-3-Bu) [12]: 5-S-3-Bu was prepared by a similar
procedure as that used for 5-S, but with 3-tert-butylsalicylaldehyde (8.8 g, 0.05 mol) to give pale red
solid (80 % yield); 1H NMR (D2O, 400 MHz): δ (ppm) 9.799.82 (m, 1H), 7.877.91 (m, 2H),
1.311.33 (m, 9H). Anal. Calcd (found): C, 47.14 (47.06); H, 4.68 (4.76); S, 11.44 (11.37). ESI-MS:
m/z = 257.
3-chloro-salicylaldehyde-5-sulfonate sodium (5-S-3-Cl) [12]: 5-S-3-Cl was prepared by a similar
procedure as that used for 5-S, but with 3-chloro-salicylaldehyde (7.8 g, 0.05 mol) to give pale yellow
solid (76 % yield); 1H NMR (D2O, 400 MHz): δ (ppm) 9.789.82 (m, 1H), 7.657.69 (m, 2H) Anal.
Calcd (found): C, 32.51 (32.46); H, 1.56 (1.59); S, 12.40 (12.31). ESI-MS: m/z = 235.
3-methoxyl-salicylaldehyde-5-sulfonate sodium (5-S-3-OMe) [12]: 5-S-3-OMe was prepared by a
similar procedure as that used for 5-S, but with 3-methoxyl-salicylaldehyde (7.6 g, 0.05 mol) to give
earthy yellow solid (70 % yield); 1HNMR (D2O, 400 MHz): δ (ppm) 10.04 (s, 1H, CHO), 7.457.55 (m,
1H), 7.117.16 (m, 1H), 3.763.80 (s, 3H). Anal. Calcd (found): C, 37.80 (37.72); H, 2.78 (2.93); S,
12.61 (12.56). ESI-MS: m/z = 231.
2-hydroxy-1-naphthaldehyd-6-sulfonate sodium (6-S-Naph) [12]: 6-S-Naph was prepared by a similar
procedure as that used for 5-S, but with 2-hydroxy-1-naphthaldehyde (8.60 g, 0.05mol) to give light
3
pink solid (52% yield); 1H NMR (D2O, 400 MHz): δ (ppm) 10.14 (s, 1H), 8.008.06 (d, 1H), 7.897.93
(d, 1H), 7.667.71 (m, 2H), 6.376.78 (d, 1H). Anal. Calcd(found): C, 48.18 (48.10); H, 2.57 (2.73); S,
11.69 (11.56). ESI-MS: m/z = 251.
4
Fig. S1 1H NMR spectra of 3-Me (top) and deprotonated 3-Me (bottom) (adding 2 equiv. of NaOH in
D2O) in CD3CN.
5
Fig. S2 Resonance structures of deprotonated Sal. Phenolic O and quinine have the same frontier
molecular orbitals calculated at B3LYP 6-31G(d,p) level of theory.
Fig. S3 Optimized structures and frontier molecular orbitals for the selected protonated (a) and
deprotonated (b) salicylaldehyde molecules calculated at B3LYP 6-31G(d,p) level of theory.
6
Fig. S4 HOMO and LUMO levels of 3-substituted protonated (a) and deprotonated (b) salicylaldehyde
molecules.
Fig. S5 HOMO and LUMO levels of other substituted protonated (a) and deprotonated (b)
salicylaldehyde molecules.
7
Fig. S6 HOMO and LUMO levels of protonated (a) and deprotonated (b) 5-sulfosalicylaldehyde
molecules.
Fig. S7 Optimized structures and frontier molecular orbitals for 5-S (SO3H) calculated at B3LYP 631G(d,p) level of theory.
0.140
4000
0.093
2000
0.047
f
3
1
 / dm mol cm
1
6000
0
0.000
200
250
300
350
400
Wavelength / nm
8
Fig. S8 Optimized structures, frontier molecular orbitals and absorption spectrum of salicylic acid
calculated at B3LYP 6-31G(d,p) level of theory.
Emission intensity / a.u.
800
add OH

600
400
200
Sal
0
add H
0
1
2
3
4
5
6

7
8
9 10 11 12 13
Cycle times
Fig. S9 Emission intensity (em = 485 nm) for protonated and deprotonated Sal in MeCN.
9
Fig. S10 X-ray single crystal structure of Sal (a and b) and 3-OMe (c).
10
(a)
(b)
0.75
0.8
14
0.6
0.50
2
Absorbance
Absorbance
pH
0.25
0.4
0.2
0.0
0.00
300
350
400
450
3
500
4
5
6
7
8
Wavelength / nm
(c)
12 13 14
10
12
(d)
pH
2
500
10 11
Emission intensity / a.u.
Emission intensity / a.u.
14
450
9
pH
550
Wavelength / nm
600
3
4
5
6
7
8
9
11
13
14
pH
Fig. S11 Absorption (a) and emission (c) spectra (excited at 378 nm) and plots of A378 (b) and emission
intensity (d) (em = 497 nm) of Sal (5.0  105 mol dm3) versus pH value in the pure aqueous B-R
buffer solution.
11
(a)
0.6
(b)
0.5
0.6
14
Absorbance
Absorbance
0.5
pH
0.4
1
0.3
0.2
0.4
0.3
0.2
0.1
0.1
0.0
300
0.0
350
400
450
500
4
5
6
7
8
9
Wavelength / nm
(c)
14
Emission intensity / a.u.
10 11 12 13 14
pH
(d)
Emission intensity / a.u.
pH
1
450
500
550
Wavelength / nm
600
4
5
6
7
8
9
10
11
12
13
14
pH
Fig. S12 Absorption (a) and emission (c) spectra (excited at 380 nm) and plots of A378 (b) and emission
intensity (d) (em = 508 nm) of 3-Me (1.0  104 mol dm3) versus pH value in the mixed solvents of
aqueous B-R buffer solution/DMSO (9:1).
12
(c)
Emission intensity / a.u.
14
pH
3
450
500
550
600
650
Wavelength / nm
Emission intensity / nm
(d)
4
5
6
7
8
9
10
11
12
13
14
pH
Fig. S13 Emission (a) spectra (excited at 390 nm) and plot emission intensity (d) (em = 510 nm) of 3Bu (1.0  104 mol dm3) versus pH value in the mixed solvents of aqueous B-R buffer solution/DMSO
(9:1).
13
(a)
Emission intensity / a.u.
12
pH
1
450
500
550
600
Wavelength / nm
Emission intensity / nm
(b)
1
2
3
4
5
6
7
8
9
10
11
12
pH
Fig. S14 Emission spectra (a) (excited at 370 nm) and plot of emission intensity (b) (em = 500 nm) of
3-F (1.0  104 mol dm3) versus pH value in the mixed solvents of aqueous B-R buffer solution/DMSO
(9:1).
14
Emission intensity / a.u.
(a)
14
pH
2
450
500
550
600
Wavelength / nm
Emission intensity / a.u.
(b)
3
4
5
6
7
8
9
10
11
12
13
14
pH
Fig. S15 Emission spectra (a) (excited at 360 nm) and plots of emission intensity (b) (em = 490 nm) of
4-NEt2 (1.0  104 mol dm3) versus pH value in the mixed solvents of aqueous B-R buffer
solution/DMSO (9:1).
15
(a)
1.2
12
pH
Absorbance
1.0
1
0.8
0.6
0.4
0.2
300
350
400
450
500
Wavelength / nm
(b)
1.2
Absorbance
1.0
0.8
0.6
0.4
0.2
0.0
1
2
3
4
5
6
7
8
9
10 11 12
pH
Fig. S16 Absorption (a) and plot of A426 (b) of 3-NO2 (1.0  104 mol dm3) versus pH value in the
mixed solvents of aqueous B-R buffer solution/DMSO (9:1).
16
(a)
Emissiojn intensity /a.u.
13
pH
1
450
500
550
600
Emission intensity / a.u.
Wavelength / nm
2
3
4
5
6
7
8
9
10 11 12 13 14
pH
Fig. S17 Emission spectra (a) (excited at 370 nm) and plots of emission intensity (b) (em = 490 nm) of
5-CO2H (1.0  104 mol dm3) versus pH value in the mixed solvents of aqueous B-R buffer
solution/DMSO (9:1).
17
(a)
Emission intensity / a.u.
12
pH
2
450
500
550
600
Wavelength / nm
Emission intensity / nm
(b)
2
3
4
5
6
7
8
9
10
11
12
pH
Fig. S18 Emission spectra (a) (excited at 380 nm) and plots of emission intensity (b) (em = 505 nm) of
3-Cl (1.0  104 mol dm3) versus pH value in the mixed solvents of aqueous B-R buffer
solution/DMSO (9:1).
18
(a)
(b)
13
0.3
Absorbance
0.3
Absorbance
0.4
0.4
pH
2
0.2
0.1
0.1
0.0
300
0.2
350
400
450
500
0.0
2
Wavelength / nm
6
7
8
9
10
11
8
9
10
11
12
13
Emission intensity / a.u.
Emission intensity / a.u.
5
(d)
12
pH
2
500
4
pH
(c)
450
3
550
600
Wavelength / nm
650
2
3
4
5
6
7
12
13
pH
Fig. S19 Absorption (a) and emission (c) spectra (excited at 390 nm) and plots of A390 (b) and emission
intensity (d) (em = 540 nm) of 3-OMe (1.0  104 mol dm3) versus pH value in the mixed solvents of
aqueous B-R buffer solution/DMSO (9:1).
19
Emission intensity / a.u.
(a)
13
pH
2
450
500
550
600
Emission intensity / a.u.
Wavelength / nm
2
3
4
5
6
7
8
9
10 11 12 13 14
pH
Fig. S20 Emission spectra (a) (excited at 360 nm) and plots of emission intensity (b) (em = 487 nm) of
4-OMe (1.0  104 mol dm3) versus pH value in the mixed solvents of aqueous B-R buffer
solution/DMSO (9:1).
20
(a)
0.4
14
Absorbance
0.3
pH
0.2
2
0.1
0.0
300
350
400
450
500
pH
(b)
0.4
Absorbance
0.3
0.2
0.1
0.0
2
3
4
5
6
7
8
9
10 11 12 13 14
pH
Fig. S21 Absorption spectra (a) and plot of A405 (b) of 5-OMe (1.0  104 mol dm3) versus pH value in
the mixed solvents of aqueous B-R buffer solution/DMSO (9:1).
21
(a)
1.2
Absorbance
1.0
12
pH
0.7
1
0.5
0.2
0.0
300
350
400
450
Wavelength / nm
1.0
Absorbance
0.8
0.6
0.4
0.2
0.0
1
2
3
4
5
6
7
8
9
10
11
12
pH
Fig. S22 Absorption spectra (a) and plot of A395 (b) of Naph (1.0  104 mol dm3) versus pH value in
the mixed solvents of aqueous B-R buffer solution/DMSO (9:1).
22
(a)
Emission intensity / a.u.
11
pH
1
450
500
550
600
Wavelength / nm
Emission intensity / a.u.
(b)
2
3
4
5
6
7
8
9
10
11
pH
Fig. S23 Emission spectra (a) (excited 370 nm) and plot of emission intensity (b) (em = 490 nm) of 5-S
(1.0  104 mol dm3) versus pH value in the in pure aqueous B-R buffer solution.
23
(a)
Emission intesity / a.u.
12
pH
2
450
500
550
600
Wavelength / nm
Emission intensity / a.u.
(b)
2
3
4
5
6
7
8
9
10
11
12
pH
Fig. S24 Emission spectra (a) (excited 370 nm) and plot of emission intensity (b) (em = 503 nm) of 5-S3-Me (1.0  104 mol dm3) versus pH value in the in pure aqueous B-R buffer solution.
24
(a)
Emission intensity / a.u.
12
pH
2
450
500
550
600
Wavelength / nm
Emission intensity / a.u.
(b)
2
3
4
5
6
7 8
pH
9 10 11 12
Fig. S25 Emission spectra (a) (excited 370 nm) and plot of emission intensity (b) (em = 502 nm) of 5-S3-Bu (1.0  104 mol dm3) versus pH value in the in pure aqueous B-R buffer solution.
25
(a)
(b) 0.3
0.3
12
Absorbance
Absorbance
pH
0.2
1
0.1
0.0
300
350
400
450
0.2
0.1
0.0
500
1
2
3
4
5
6
Wavelength / nm
7
8
9
10
11
12
pH
(c)
Emission intensity / a.u.
Emission intensity / a.u.
(d)
13
pH
2
450
500
550
Wavelength / nm
600
650
1
2
3
4
5
6
7
8
9
10
11
12
pH
Fig. S26 Absorption (a) and emission (c) spectra (excited at 380 nm) and plots of A380 (b) and emission
intensity (d) (em = 520 nm) of 5-S-3-OMe (1.0  104 mol dm3) versus pH value in the in pure
aqueous B-R buffer solution.
26
(a)
0.6
Absorbance
12
pH
0.4
1
0.2
0.0
350
400
450
500
Wavelength / nm
(b)
Absorbance
0.6
0.4
0.2
0.0
1
2
3
4
5
6
7
8
9
10
11
12
pH
Fig. S27 Absorption spectra (a) and plot of A391 (b) of 6-S-Naph (1.0  104 mol dm3) versus pH value
in the pure aqueous B-R buffer solution.
27
Emission intensity / a.u.
(a)
5-S-3-Cl
+
Ag
3+
Al
(b)
450
3+
Fe
+
Li
2+
Mn
500
550
2+
Cd
3+
Ce
2+
Co
3+
Cr
2+
Cu
2+
Ni
2+
Pb
2+
Sr
2+
Zn
600
Wavelength / nm
Fig. S28 Emission spectra (excited at 380 nm) of 5-S-3-Cl (1.0  104 mol dm3) upon adding 2.0 equiv.
of metal ions at pH = 4.6 (a) and 7.0 (b) value in the pure aqueous B-R buffer solution.
28
Table S1 The energy gap (HOMOLUMO) and energy (eV) of frontier molecular orbitals for all the
protonated salicylaldehyde molecules.
Sal
3-NO2
3-F
3-Cl
3-Me
3-Bu
3-OMe
LUMO+1
0.121
2.136
0.189
0.425
0.030
0.074
0.144
LUMO
1.926
2.784
2.117
2.216
1.837
1.862
1.782
HOMO
6.396
7.191
6.468
6.546
6.231
6.239
5.846
HOMO-1
7.402
7.745
7.423
7.405
7.155
7.164
6.935
Energy gap
4.47
4.41
4.35
4.33
4.39
4.38
4.06
4-OMe
5-OMe
4-NEt2
5-CO2H
Naph
LUMO+1
0.041
0.074
0.252
1.386
0.653
LUMO
1.632
1.889
1.270
2.212
2.065
HOMO
6.317
5.752
5.568
6.789
6.092
HOMO-1
6.570
7.355
6.089
7.665
6.652
Energy gap
4.69
3.86
4.30
4.58
4.03
5-S
5-S-3-Cl
5-S-3-Me
5-S-3-tBu
5-S-3-OMe
6-S-Naph
LUMO+1
3.0145
2.671
3.039
2.923
3.022
2.300
LUMO
0.962
0.647
1.002
0.924
0.885
0.732
HOMO
2.016
2.242
1.984
2.032
2.042
2.059
HOMO-1
2.688
2.949
2.639
2.698
2.718
2.779
energy gap
2.98
2.89
2.99
2.96
2.93
2.79
29
Table S2 The energy gap (HOMOLUMO) and energy (eV) of frontier molecular orbitals for all the
deprotonated salicylaldehyde molecules.
Sal
3-NO2
3-F
3-Cl
3-Me
3-tBu
3-OMe
LUMO+1
5.307
3.115
5.155
4.867
5.210
4.938
5.238
LUMO
3.462
1.827
3.331
3.026
3.465
3.274
3.574
HOMO
0.421
1.555
0.565
0.848
0.436
0.655
0.300
HOMO1
0.848
1.698
1.145
1.384
0.955
1.146
0.982
Energy gap
3.88
3.38
3.90
3.87
3.90
3.93
3.87
4-OMe
5-OMe
4-NEt2
5-CO2H
Naph
LUMO+1
5.238
5.156
4.801
3.246
3.629
LUMO
3.492
3.274
3.383
2.837
2.786
HOMO
0.518
0.491
0.546
1.282
0.813
HOMO1
0.900
0.982
0.928
1.582
1.098
Energy gap
4.01
3.77
3.93
4.12
3.60
5-S
5-S-3-Cl
5-S-3-Me
5-S-3-tBu
5-S-3-OMe
6-S-Naph
LUMO+1
7.969
7.424
7.856
7.516
7.721
6.217
LUMO
6.132
5.682
6.103
5.859
5.957
5.208
HOMO
2.343
1.913
2.297
2.042
2.174
1.600
HOMO1
1.695
1.180
1.577
1.345
1.418
1.091
energy gap
3.79
3.77
3.81
3.82
3.78
3.61
30