Supporting Information

A squaraine-based sensor for colorimetric detection of CO2

gas in aqueous medium through an unexpected recognition

mechanism

Jianqi Sun‡a,b, Xiangjuan Zheng‡a, Xinjie Wua, Dong Lia, Guomin Xiaa, Shuxian Yu a, Qiming Yu

and Hongming Wanga*

a College of Chemistry and Institute for Advanced Study, Nanchang University, Nanchang, Jiangxi 330031, China

b College of Chemistry and Envioronmental Engineering, Jiujiang University, Jiujiang, Jiangxi 332005, China

Detection Limit [1]. The detection limit was calculated on the basis of the UV-Vis

titration. The UV-Vis spectrum of SQM (7.5 μM) in MeCN-H2O (V : V = 90 : 10)

was measured 12 times, and the standard deviation of blank measurement was

achieved. To gain the slope, the absorbance at 627 nm versus amount of pure CO2 gas

was plotted. The detection limit was calculated using the following equation:

Detection limit = 3σ/k (1)

Where σ is the standard deviation of blank measurement, and k is the slope

between the absorbance versus the volume of pure CO2 gas (VCO2).

References

[1] S. Samanta, S. Goswami, M. N. Hoque, A. Rameshm and G. Das, Chem. Commun.,

2014, 50, 11833.

‡These authors contributed equally to this work.

Electronic Supplementary Material (ESI) for Analytical Methods.This journal is © The Royal Society of Chemistry 2017

Captions:

Fig. S1 UV-Vis spectral changes obtained during the course of titrating sensor SQM

(7.5 μM) with 50-fold weak base EA, DEA, TEA and Py in MeCN respectively.

Fig. S2 UV-Vis spectral changes obtained during the course of titrating sensor SQM

(7.5 μM) with DBU in MeCN. Inset: The corresponding plots of absorbance at

indicated wavelengths versus additional DBU.

Fig. S3 UV-Vis spectral changes obtained during the course of titrating sensor SQM

(7.5 μM) with TMG in MeCN. Inset: The corresponding plots of absorbance at

indicated wavelengths versus additional TMG.

Fig. S4 UV-Vis spectral changes obtained during the course of titrating sensor SQM

(7.5 μM) with [NBu4]F in MeCN. Inset: The corresponding plots of absorbance at

indicated wavelengths versus additional [NBu4]F.

Fig. S5 UV-Vis spectral changes obtained during the course of titrating sensor SQM

(7.5 μM) with (a) 2-fold TBD; (b) 5-fold DBU in MeCN then bubbled with different

volumes of CO2 gas in a sealed cuvette.

Fig. S6 (a) UV-Vis spectral changes obtained during the course of titrating sensor

SQM (7.5 μM) with DBU in MeCN-H2O (V : V = 90 : 10); (b) then bubbled with

different volumes of CO2 gas in a sealed cuvette. Inset: The corresponding plots of

absorbance at indicated wavelengths versus additional DBU or volume of CO2 gas.

Fig. S7 UV-Vis spectrum of precursor SQ (7.5 μM) in MeCN-H2O (V : V = 90 : 10).

Fig. S8 The absorbance of SQM (7.5 μM) at 627 nm in MeCN-H2O with different

volume fractions of H2O after addition of 20 eq TBD (the black bar) followed by

bubbling 5 mL CO2 gas (the green bar) in a sealed cuvette.

Fig. S9 The absorbance of SQM (7.5 μM) at 627 nm with the addition of TBD (20 eq)

versus the volume of pure CO2 gas in MeCN-H2O (V : V = 90 : 10).

Fig. S10 The absorbance of SQM (7.5 μM) at 627 nm with the addition of DBU (20

eq) versus the volume of pure CO2 gas in MeCN-H2O (V : V = 90 : 10).

Fig. S11 The mass spectrometry analysis of SQM in MeCN with addition of TBD in

positive mode.

Fig. S12 The mass spectrometry analysis of SQM in MeCN-H2O (V : V = 90 : 10)

with addition of TBD in positive mode.

Fig. S13 The mass spectrometry analysis of SQM in MeCN-H2O (V : V = 90 : 10)

with addition of TBD followed by CO2 gas in positive mode.

Fig. S14 The mass spectrometry analysis of SQM in MeCN-H2O (V : V = 90 : 10)

with addition of NaOH in positive mode.

Fig. S15 The mass spectrometry analysis of SQM in MeCN-H2O (V : V = 90 : 10)

with addition of NaOH followed by CO2 gas in positive mode.

Fig. S16 The absorbance of SQM (7.5 μM) at 627 nm with the addition of NaOH

(300 eq) versus the volume of pure CO2 gas in MeCN-H2O (V : V = 90 : 10).

Fig. S17 The mass spectrometry analysis of SQM in MeCN-H2O (V : V = 90 : 10)

with addition of TBD followed by CO2 gas in negative mode.

Fig. S18 Partial 1H-NMR spectra obtained during the course of titrating sensor SQM

(5.0 mM) with NaOH followed by CO2 in DMSO-d6.

Fig. S19 1H NMR spectrum of SQM

Fig. S20 13C NMR spectrum of SQM

Fig. S21 The mass spectrometry analysis of SQM in MeCN in positive mode.

300 400 500 600 7000.0

0.5

1.0

1.5

2.0

2.5

3.0Ab

sorb

ance

Wavelength/nm

SQM SQM+50eq EA SQM+50eq DEA SQM+50eq TEA SQM+50eq Py

Fig. S1 UV-Vis spectral changes obtained during the course of titrating sensor SQM

(7.5 μM) with 50-fold weak base EA, DEA, TEA and Py in MeCN respectively.

300 400 500 600 7000.0

0.5

1.0

1.5

2.0

2.5

3.0Ab

sorb

ance

Wavelength/nm

SQM Current SQM+5eq DBU

0 1 2 3 4 50.0

0.5

1.0

1.5

2.0

2.5

3.0

At 627nm

Abso

rban

ce

Equiv.DBU

Fig. S2 UV-Vis spectral changes obtained during the course of titrating sensor SQM

(7.5 μM) with DBU in MeCN. Inset: The corresponding plots of absorbance at

indicated wavelengths versus additional DBU.

300 400 500 600 7000.0

0.5

1.0

1.5

2.0

2.5

3.0Ab

sorb

ance

Wavelength/nm

SQM Current SQM+20eq TMG

0 5 10 15 200.0

0.5

1.0

1.5

2.0

2.5

3.0

At 627Ab

sorb

ance

Equiv.TMG

Fig. S3 UV-Vis spectral changes obtained during the course of titrating sensor SQM

(7.5 μM) with TMG in MeCN. Inset: The corresponding plots of absorbance at

indicated wavelengths versus additional TMG.

300 400 500 600 7000.0

0.5

1.0

1.5

2.0

2.5

3.0Ab

sorb

ance

Wavelength/nm

SQM Current SQM+50eq F-

0 10 20 30 40 500.0

0.5

1.0

1.5

2.0

2.5

3.0

At 627nmAb

sorb

ance

Equiv.[NBu4]F

Fig. S4 UV-Vis spectral changes obtained during the course of titrating sensor SQM

(7.5 μM) with [NBu4]F in MeCN. Inset: The corresponding plots of absorbance at

indicated wavelengths versus additional [NBu4]F.

300 400 500 600 7000.0

0.5

1.0

1.5

2.0

2.5

3.0Ab

sorb

ance

Wavelength/nm

SQM SQM+2eq TBD Current SQM+2eq TBD+5ml CO2

(a)

300 400 500 600 7000.0

0.5

1.0

1.5

2.0

2.5

3.0

Abso

rban

ce

Wavelength/nm

SQM SQM+5eq DBU Current SQM+5eq DBU+5ml CO2

(b)

Fig. S5 UV-Vis spectral changes obtained during the course of titrating sensor SQM

(7.5 μM) with (a) 2-fold TBD; (b) 5-fold DBU in MeCN then bubbled with different

volumes of CO2 gas in a sealed cuvette.

300 400 500 600 7000.0

0.5

1.0

1.5

2.0

2.5

3.0Ab

sorb

ance

Wavelength/nm

SQM Current SQM+50eq DBU

0 10 20 30 40 500.0

0.5

1.0

1.5

2.0

2.5

3.0

At 627nmAb

sorb

ance

Equiv.DBU

(a)

300 400 500 600 7000.0

0.5

1.0

1.5

2.0

2.5

3.0

Abso

rban

ce

Wavelength/nm

SQM SQM+50eq DBU Current SQM+50eq DBU+10ml CO2

0 1 2 3 4 5 6 7 8 9 100.0

0.5

1.0

1.5

2.0

2.5

3.0

At 627nm

Abso

rban

ce

VCO2(ml)

(b)

Fig. S6 (a) UV-Vis spectral changes obtained during the course of titrating sensor

SQM (7.5 μM) with DBU in MeCN-H2O (V : V = 90 : 10); (b) then bubbled with

different volumes of CO2 gas in a sealed cuvette. Inset: The corresponding plots of

absorbance at indicated wavelengths versus additional DBU or volume of CO2 gas.

300 400 500 600 7000.0

0.5

1.0

1.5

2.0

2.5

Abso

rban

ce

Wavelength/nm

Fig. S7 UV-Vis spectrum of precursor SQ (7.5 μM) in MeCN-H2O (V : V = 90 : 10).

0 10 20 30 40 500.0

0.5

1.0

1.5

2.0

2.5

Abso

rban

ce

Water Volume Fraction (%) Fig. S8 The absorbance of SQM (7.5 μM) at 627 nm in MeCN-H2O with different volume fractions of H2O after addition of 20 eq TBD (the black bar) followed by bubbling 5 mL CO2 gas (the green bar) in a sealed cuvette.

0.00 0.05 0.10 0.15 0.200.4

0.5

0.6

0.7

0.8

0.9Ab

sorb

ance

(a.u

.)

VCO2 (ml)

At 627 nm Y=0.44747+2.12145X,

R=0.99738

Fig. S9 The absorbance of SQM (7.5 μM) at 627 nm with the addition of DBT (20 eq)

versus the volume of pure CO2 gas in MeCN-H2O (V : V = 90 : 10).

The detection limit in MeCN-H2O (V : V = 90 : 10) (3.0 ml) was calculated to be

about 1.59*10-6 M (ca. 39.0 ppm, 1atm, 25°C)

0.0 0.1 0.2 0.3

0.2

0.4

0.6

0.8

VCO2 (ml)

Abso

rban

ce (a

.u.)

At 627 nm Y=0.26298 + 1.68529X,

R=0.99447

Fig. S10 The absorbance of SQM (7.5 μM) at 627 nm with the addition of DBU (20

eq) versus the volume of pure CO2 gas in MeCN-H2O (V : V = 90 : 10).

The detection limit in MeCN-H2O (V : V = 90 : 10) (3.0 ml) was calculated to be

about 2.0*10-6 M (ca. 49.1 ppm, 1atm, 25°C)

SQ-OCH3+TBD #23-76 RT: 0.09-0.24 AV: 54 NL: 4.69E3T: ITMS + c ESI Full ms [100.00-1000.00]

100 150 200 250 300 350 400 450 500 550 600 650 700 750 800 850 900 950 1000m/z

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

95

100

Rel

ativ

e A

bund

ance

749.09610.24

594.31140.06750.11

592.27

611.24

338.34

439.33 578.28

717.14 751.12612.26210.20 815.51564.44 683.55 859.62339.36 810.32 903.57624.29440.38 854.27 947.48498.45 546.41 772.66 860.65 976.00652.43141.10 539.39315.07242.35 369.19 457.39167.02 534.50424.38281.14139.13

Fig. S11 The mass spectrometry analysis of SQM with addition of TBD in MeCN in

positive mode.

SQ-OCH3+TBD+CH3CN-H2O #187-266 RT: 0.57-0.80 AV: 80 NL: 2.06E4T: ITMS + c ESI Full ms [100.00-1000.00]

100 150 200 250 300 350 400 450 500 550 600 650 700 750 800 850 900 950 1000m/z

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

95

100

Rel

ativ

e A

bund

ance

140.03

564.40

565.39428.88

141.08439.30

515.89 749.01566.41376.98210.21 771.62440.34 859.55739.20341.31 605.10 815.56 903.55652.34 683.53516.96 947.55 991.79378.06315.04142.07 211.23 498.57112.04 278.86

Fig. S12 The mass spectrometry analysis of SQM in MeCN-H2O (V : V = 90 : 10)

with addition of TBD in positive mode.

SQ-OCH3+TBD+CO2+CH3CN+H2O #75-180 RT: 0.25-0.55 AV: 106 NL: 2.91E4T: ITMS + c ESI Full ms [100.00-1000.00]

100 150 200 250 300 350 400 450 500 550 600 650 700 750 800 850 900 950 1000m/z

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

95

100R

elat

ive

Abu

ndan

ce140.02

564.38

428.87565.37

141.07749.03210.20 515.86376.98 750.06566.39429.92341.28 605.11 739.18315.02 687.83516.92 887.83 976.03865.25211.21 915.96378.03 768.07675.02439.25278.81142.09112.04 498.41

Fig. S13 The mass spectrometry analysis of SQM in MeCN-H2O (V : V = 90 : 10)

with addition of TBD followed by CO2 gas in positive mode.

SO-OCH3+NaOH+CH3CN-H2O #33-231 RT: 0.12-0.66 AV: 199 NL: 6.49E3T: ITMS + c ESI Full ms [100.00-1000.00]

100 150 200 250 300 350 400 450 500 550 600 650 700 750 800 850 900 950 1000m/z

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

95

100

Rel

ativ

e A

bund

ance

871.03

872.06

140.07

727.60683.58 771.58 815.59

639.56

859.60 903.48

595.55369.14

986.69942.99793.34855.06

728.65 985.56551.52 705.41904.67 947.68640.65

447.28926.64 948.71661.42507.53 596.61

969.21428.90 552.57 617.38370.20 479.17141.09 508.58 586.21313.19 362.69 419.44202.20 294.74226.98180.15138.18

Fig. S14 The mass spectrometry analysis of SQM in MeCN-H2O (V : V = 90 : 10)

with addition of NaOH in positive mode.

SQ-OCH3+NaOH+CO2+CH3CN+H2O #50-225 RT: 0.17-0.65 AV: 176 NL: 1.56E4T: ITMS + c ESI Full ms [100.00-1000.00]

100 150 200 250 300 350 400 450 500 550 600 650 700 750 800 850 900 950 1000m/z

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

95

100R

elat

ive

Abu

ndan

ce871.02

872.03

873.02140.06 815.60771.59727.59683.57 859.58447.31

639.58 903.55369.15 816.63595.55 772.61728.65425.27 947.60684.62551.55452.37 640.62 735.69 991.65596.61 930.54817.64424.39 507.58293.36 487.47253.30 657.72 685.65141.10 332.76180.11128.94

Fig. S15 The mass spectrometry analysis of SQM in MeCN-H2O (V : V = 90 : 10)

with addition of NaOH followed by bubbling CO2 gas in positive mode.

0.00 0.05 0.10 0.15 0.20 0.25

0.2

0.4

0.6

0.8

1.0

At 627 nm Y=0.25472 + 2.81449X

R=0.99871

VCO2(ml)

Abso

rban

ce (a

.u.)

Fig. S16 The absorbance of SQM (7.5 μM) at 627 nm with the addition of NaOH

(300 eq) versus the volume of pure CO2 gas in MeCN-H2O (V : V = 90 : 10).

The detection limit in MeCN-H2O (V : V = 90 : 10) (3.0 ml) was calculated to be

about 1.20*10-6 M (ca. 29.4 ppm, 1atm, 25°C)

SQ-OCH3+TBD+CH3CN+H2O- #16 RT: 0.09 AV: 1 NL: 1.23E1T: ITMS - c ESI Full ms [100.00-1000.00]

100 150 200 250 300 350 400 450 500 550 600 650 700 750 800 850 900 950 1000m/z

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

95

100

Rel

ativ

e A

bund

ance

809.17

863.04690.82598.37864.55

766.11 893.10

943.79

778.45499.15 946.33

695.97

902.22844.23637.16

610.36 663.53310.83 913.75591.46 955.55

710.72

524.07 558.26 997.10

417.40

985.41

Fig. S17 The mass spectrometry analysis of SQM in MeCN-H2O (V : V = 90 : 10)

with addition of TBD followed by CO2 gas in negative mode.

N O

O Na

b

cd

e

N O

ON

a′b′

c′d′

e′OH-

e′′

ae

bd

d′′

b′′a′

OH

Fig. S18 Partial 1H-NMR spectra obtained during the course of titrating sensor SQM

(5.0 mM) with NaOH followed by CO2 in DMSO-d6.

Fig. S19 1H NMR spectrum of SQM

N O

O N

SQM

Fig. 20 13C NMR spectrum of SQM

N O

O N

SQM

CF3SO3

SQ-OCH3 #85-161 RT: 0.25-0.44 AV: 77 NL: 1.27E5T: ITMS + c ESI Full ms [200.00-1000.00]

200 250 300 350 400 450 500 550 600 650 700 750 800 850 900 950 1000m/z

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

95

100R

elat

ive

Abu

ndan

ce

439.31

440.26

441.30727.55 771.56683.54 815.57639.53595.52 859.56551.51 903.56507.50 947.56463.50424.40 741.39 785.40 991.60697.44641.58252.21 369.26339.38222.22 277.30

Fig. 21 The mass spectrometry analysis of SQM in MeCN in positive mode.