S1

Supporting Information

Surface Motifs Regulated Aggregation Induced Emission in Gold-

Silver Nanoclusters

Dipankar Baina,Subarna Maitya, and Amitava Patraa,b*

a,bSchool of Materials Sciences, Indian Association for the Cultivation of Science,

Kolkata 700 032, India

bInstitute of Nano Science and Technology, Habitat Centre, Sector 64, Phase 10,

Mohali 160062, India

*Author to whom correspondence should be addressed. Electronic mail: msap@iacs.res.in

Telephone: (91)-33-2473-4971. Fax: (91)-33-2473-2805

Electronic Supplementary Material (ESI) for ChemComm.This journal is © The Royal Society of Chemistry 2020

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Experimental Section

Chemicals and methods:

Chemicals: Tetrachloroauric acid trihydrate (HAuCl4·3H2O), silver nitrate (AgNO3), N-(2-

Mercaptopropionyl)glycine, glutathione reduced (GSH), were purchased from Sigma-Aldrich.

Other chemicals such as sodium borohydride (NaBH4), sodium hydroxide granules (NaOH),

methanol, and ethanol were purchased from Merck. High purity water (∼18.2 MΩ) was used

throughout the experiment. All the chemicals of highest purity grade were used without further

purification.

Methods:

Synthesis of mono-metallic and bi-metallic nanoclusters:

Luminescent gold and gold-silver alloy nanoclusters were synthesized by two step synthesis. In

the first, polydisperse non luminescent Au nanoclusters were synthesized using N-(2-

mercaptopropionyl)glycine (MPGH) as capping agent. Then, glutathione (GSH) assisted ligand

exchange process was employed to prepare fluorescent Au and AuAg alloy cluster.

MPG-protected non luminescent Au NCs:

In a typical synthesis, 4 mL of 25mM HAuCl3.3H2O was added to a 100 mL MeOH in 200 mL

conical flask at 0°C (ice bath). Then, 160 mg of MPGH ligand was added to the reaction mixture

and the reaction was allowed to stirrer for 30 minutes. After that, freshly prepared ice cold NaBH4

(200 mg, in 20 mL water) was rapidly injected in to the reaction mixture under vigorous stirring,

and a black particles were formed immediately. The reaction was further allowed to stirring for

another 30 minutes for complete reduction. Finally, the black precipitate was collected by

centrifugation at 10000 rpm for 10 minutes. The particles washed at least two times with

methanol/water (3:1) mixture to remove the excess salts, precursor. Then, the particles was kept

overnight at room temperature to obtain dry polydisperse nanoclusters. The as prepared non

luminescent Au NCs were dissolved in water for further experiment.

Glutathione directed synthesis of Au and AuAg alloy nanoclusters:

Red emitting Au NCs were prepared from as-prepared polydisperse Au NCs; typically 1.25 mL

MPG capped Au NCs added to 8.75 mL deionized water. Then excess glutathione (307 mg) was

added to the reaction mixture and stirred at 55°C. The reaction was monitored using absorption

and photoluminescence (PL) spectroscopy, the reaction is completed within 18 hours. The as-

prepared Au NCs emits red color under the exposures of UV lamp (365 nm). For bi-metallic AuAg

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NCs synthesis different amount of AgNO3 (25 mM) was added during the ligand exchange process.

The emission maxima of AuAg NCs are changed with varying the concentration of Ag+ ion.

Typically, strong red emitting NCs (r-AuAg) is obtained when 100 µL Ag+ was added and yellow

emitting NCs (y-AuAg) was obtained upon addition of 200 µL of Ag+. The synthesis scheme of

mono-metallic Au NCs and bi-metallic AuAg NCs is illustrated in scheme 1.

Scheme 1. Schematic representation of the synthesis of Au and AuAg nanoclusters with tunable

emission

Instrumentation

The optical absorption spectra were taken with a UV-vis spectrophotometer (Shimadzu) using a

cuvette with a path length of 1 cm at room temperature. The PL spectra of all of the samples were

taken with a Fluoro Max-P (HORIBA JobinYvon) luminescence spectrophotometer. The

transmission electron microscopy (TEM) was performed on a JEOL-JEM-2100F transmission

electron microscopy system at an accelerating voltage of 200 kV. The samples for TEM analysis

were prepared by drop casting of NCs solution onto a copper grid covered by a carbon film. The

X-ray photoelectron spectroscopy (XPS) (Omicron Nanotechnology instrument) study was carried

out to determine the binding energy. Raman spectra were recorded by using Horiba JobinYvon,

(T64000 model) instrument by exciting the samples at 632 nm laser beam. Fourier-transform

infrared (FTIR) spectroscopy analyses were performed on a SHIMADZU made FTIR-8300

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spectrometer using KBr pellets. The zeta potential and dynamic light scattering (DLS) sizes were

measured with a Malveron Zetasizer instrument. For the time correlated single photon counting

(TCSPC) analysis, the samples were excited at 415 nm using a Spectra LED light source for the

measurement of phosphorescence lifetimes. The typical full width at half-maximum (FWHM) of

the system response using a liquid scatter was about 90 ps. The fluorescence decays were collected

on a Hamamatsu MCP photomultiplier. Equation (1) is used to analyze the experimental time-

resolved fluorescence decays, P(t):

n

iii tbtP )/(exp)( (1)

Here, n is the number of emissive species, b is the baseline correction (“DC” offset), and αi and τi

are, respectively, the pre-exponential factor and the excited-state fluorescence decay time

associated with the ith component. The average decay time, < τ >, is calculated from following

equation.24

(2)

n

iii

1

Where and is contribution of the decay component. iii / i

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(B)(A)

200 300 400 500 600 700 8000.0

0.3

0.6

0.9

1.2

Abso

rpba

nce

Wavelength (nm)

(C)

Fig. S1. TEM images of MPG-capped Au NCs with scale bar (A) 50 nm, (B) 20 nm and (C)

absorption spectra Au NCs and inset shows the digital picture of NCs powder.

4000 3500 3000 2500 2000 1500 1000 500

-S-H bond

Wavenumber (cm-1)

Tran

smitt

ance

(%)

GSH (A)

4000 3500 3000 2500 2000 1500 1000 500

No -S-H bond

Wavenumber (cm-1)

(B)

Tran

smitt

ance

(%)

Au-GSH

Fig. S2. FTIR spectrum of (A) glutathione (GSH), and (B) bimetallic AuAg NCs capped by GSH.

S6

Increasing Ag ratio in Au Ag NCs (Au:Ag)

(B)AuNC r-AuAg y-AuAg

a b c d e f

500 550 600 650 700 7500.0

2.0x105

4.0x105

6.0x105

8.0x105

1.0x106

1.2x106

1.4x106

a b c d e fPL

Inte

nsity

(a.u

)

Wavelength (nm)

(A)

Ag ratio in

AuAg NCs increases

Fig. S3. (A)Tuning of emission wavelength of Au NCs with different Au/Ag molar ratio (a) 1:0,

(b) 1:0.14, (c) 1:0.71, (d) 1:0.98, (e) 1:1.36 and (d) 1:1.51 and (B) Digital picture of corresponding

NCs under UV-light excitation (365 nm).

0 5 10 15 20 25 3005

101520253035

Num

ber

(%)

Size (nm)

Size = 11.7 nm

r-AuAg NCs(B)

0 5 10 15 20 25 300

5

10

15

20

25

30

35

Num

ber

(%)

Size (nm)

(C) y-AuAg NCs

Size = 11.1 nm

0 5 10 15 20 25 30

0

5

10

15

20

25

Num

ber

(%)

Size (nm)

(A) Au NCs

Size= 13.7 nm

Fig. S4. DLS size distribution plot of (A) Au NCs, (B) r-AuAg NCs and (C) y-AuAg NCs.

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500 550 600 650 700 750 8000.0

2.0x105

4.0x105

6.0x105

8.0x105

1.0x106

PL In

tens

ity (a

.u)

Wavelength (nm)

pH=1 pH=3 pH=5 pH=7r-AuAg NCs

Fig. S5. Absorption spectra of (a) Au NCs, (b) r-AuAg NCs and (c) y-AuAg NCs and inset shows

the zoomed view.

Fig. S6. PL spectra of r-AuAg NCs at different pHs under 400 nm excitation wavelength.

300 400 500 600 7000.0

0.2

0.4

0.6

c

b

Abs

orba

nce

Wavelength (nm)

a300 400 500 600 700 800 900

0.00

0.01

0.02

0.03

0.04

0.05

c

b

Abs

orba

nce

Wavelength (nm)

a

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600 700 8000.0

3.0x105

6.0x105

9.0x105

1.2x106

PL In

tens

ity (a

.u)

Wavelength (nm)

340 nm 360 nm 380 nm 400 nm 420 nm 440 nm

(A)

500 600 700 8000.0

2.0x105

4.0x105

6.0x105

8.0x105

PL In

tens

ity (a

.u)

Wavelength (nm)

340 nm 360 nm 380 nm 400 nm 420 nm 440 nm

(B)

Fig.S7. Excitation wavelength dependent emission spectra of (A) r-AuAg NCs and (B) y-AuAg

NCs

550 600 650 700 750 8000.0

2.0x105

4.0x105

6.0x105

8.0x105

1.0x106

PL In

tens

ity (a

.u)

Wavelength (nm)

GSH AuAg NCs

(A) (B)

AuAg NCs GSH

Fig. S8. Emission spectra of (A) AuAg NCs and control experiment without metal precursor, and

(B) digital picture of control reaction and AuAg NCs under UV-light excitation (365 nm)

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500 600 700 8000.0

2.0x105

4.0x105

6.0x105

8.0x105

1.0x106

PL In

tens

ity (a

.u)

Wavelength (nm)

Ag-GSH complex AuAg NCs

Fig. 9. Emission spectra of AuAg NCs and Ag-GSH complex.

80 82 84 86 88 90 92

Au0

AuI

AuI

Au0

4f5/2

Inte

nsity

(a.u

)

Binding Energy (eV)

(A) 4f7/2

80 82 84 86 88 90 92

4f5/2

4f7/2

AuI

AuI

Au0

Au0

Inte

nsity

(a.u

)

Binding Energy (eV)

(B)

80 82 84 86 88 90 92

4f7/2

4f5/2

AuI

Au0

AuI

Au0

Inte

nsity

(a.u

)

Binding Energy (eV)

(C)

364 368 372 3761.0x104

1.5x104

2.0x104

2.5x104

3.0x104

3d3/2

Inte

nsity

(a.u

)

Binding Energy (eV)

3d5/2(D)

Fig. S10. X-ray photoelectron spectra of Au-4f of (A) Au NCs, (B) r-AuAg NCs and (C) y-AuAg

NC. (D) XPS spectrum of Ag-3d in y-AuAg NCs, dotted line indicates position of Ag(0).

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KCl

AuAg NC AuAg NC

Fig. S11. No Ag+ ion is present in AuAg NCs as there is no precipitation of AgCl after addition of

KCl solution.

(B)(A)

Fig. S12. AFM images of (A) r-AuAg NCs and (B) y-AuAg NCs

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Fig. S13. UV-Vis absorption spectra of (A) r-AuAg and (B) y-AuAg NC with (a) fv=0%, (b)

fv=60% and (c) fv=90% ethanol/water mixture.

500 550 600 650 700 7500

1x105

2x105

3x105

4x105

5x105

Inte

nsity

(a.u

)

Wavelength (nm)

0 10 20 30 40 50 60 70 80 90

(C)

0

90

X 12

600 700 8000

1x105

2x105

3x105

PL In

tens

ity

Wavelength (nm)

0 10 20 30 40 50 60 70 80 90

(B)

0

90

X 4

500 600 7000

1x105

2x105

3x105

No ProminentChangePL

Inte

nsity

(a.u

.)

Wavelength (nm)

0 10 20 30 40 50 60 70 80 90

(A)

Fig. S14. PL spectra of (A) Au NCs, (B) r-AuAg NCs and (C) y-AuAg NCs in water-EtOH mixture

with volume fraction (fv) = 0-90%.

300 400 500 6000.0

0.2

0.4

0.6

0.8

1.0 a b c

Abs

orba

nce

Wavelength (nm)

(B)

300 400 500 6000.00

0.25

0.50

0.75

1.00

Abs

orba

nce

Wavelength (nm)

a b c

(A)

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200 300 400 500 600 700 8000.0

0.3

0.6

0.9

1.2

Nor

mal

ized

Inte

nsity

Wavelength (nm)

195 nm(B)

400 500 600 700 8000.0

0.3

0.6

0.9

1.2N

orm

aliz

ed In

tens

ity

Wavelength (nm)

307 nm(A)

Fig. S15. Stokes shift of (A) r-AuAg NCs and (B) y-AuAg, respectively.

10 20 30 40100

101

102

103

b

Cou

nts (

log)

Time (s)

a

(B)

10 20 30 40

100

101

102

103

Cou

nts (

in lo

g)

Time (s)

(A)

Fig. S16. Time resolved decay curves of (A) Au NCs and (B) r-AuAg NCs (a) fv=0% and (b) fv=

60 % ethanol (λex=415 nm).

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Table 1: Time-resolved fluorescence data of Au NCs, AuAg NCs at different emission

wavelengths

Systems Excitation(Wavelength)

Emission(Wavelength)

s) s) s) <>s)

Au NCs 400 7351.34

(0.52)2.69

(0.32)5.39

(0.16)2.42

Red-AuAg NCs400

674 1.23(0.48)

2.47(0.36)

4.95(0.16)

2.27

Red-AuAg NCs(in 60% Ethanol)

400620 1.36

(0.48)2.78

(0.33)5.57

(0.19) 2.62

Yellow-AuAgNCs

400 574 0.53(0.60)

2.14(0.40)

----- 1.17

Yellow-AuAgNCs

(in 60% Ethanol)

400564 1.15

(0.55)2.31

(0.10)4.62

(0.35)2.48