Supporting Information

Supporting Information Sub-Picomolar Recognition of Cr 3+ Through Bioinspired Organic-Inorganic Ensemble Utilization Gourab Dey a,, Mangili Venkateswarulu, a, Venkateswaran Vivekananthan, a Avijit Pramanik, b Venkata Krishnan, a * and Rik Rani Koner a * a School of Basic Sciences and Advanced Materials Research Center, Indian Institute of Technology Mandi, Kamand, Mandi-1755, Himachal Pradesh, India. b Department of Chemistry and Biochemistry, Jackson State University, Jackson, Mississippi 39217, USA. E-mail address: rik@iitmandi.ac.in, vkn@iitmandi.ac.in S. No Content No. 1 General information - 2 Comparison of potential of L with other reported Cu 2+ - specific/selective molecular probes Table S1 3 Crystal data and structure refinement for L Cu 2+ complex Table S2 4 5 1 H NMR spectra of L Figure S1 13 C NMR spectra of L Figure S2 6 HRMS spectra of L Figure S3 7 ORTEP and packing diagram of L-Cu 2+ complex Figure S4 8 UV-visible spectra of L Figure S5 9 Fluorescence emission titration spectra of L Figure S6 1 Fluorescence response of L in different ph Figure S7 11 UV-vis spectra of L upon the addition of Cu 2+ Figure S8 12 UV-vis spectra of L upon the addition of Cr 3+ Figure S9 S1

13 Cu 2+ ion selectivity of L Figure S1 14 Fluorescence titration of L with Cu 2+ in 4:1 methanol-buffer system and detection limit calculation Figure S11 15 Fluorescence titration of L with Cu 2+ and binding ratio graph Figure S12 16 UV-vis spectra of L-Cu 2+ complex in the presence of Cr 3+ Figure S13 17 Fluorescence titration of L-Cu 2+ with Cr 3+ in 1:1 methanol-buffer system and detection limit calculation Figure S14 18 Fluorescence life time spectra of L, L-Cu 2+, L+Cu 2+ +Cr 3+ and L- Cr 3+ Figure S15 19 Binding constant calculation for L-Cu 2+ Figure S16 2 Binding constant calculation for L-Cr 3+ Figure S17 21 Cr 3+ ion selectivity bar graph of L-Cu 2+ Figure S18 22 Fluorescence spectra of L upon the addition of Cu 2+ ( to 6.333 pm) in methanol: buffer (4:1) system. Figure S19 23 Job plots for L-Cu 2+ complex Figure S2 24 Job plots for L-Cr 3+ complex Figure S21 25 HRMS spectra of L-Cr 3+ in acetonitrile Figure S22 26 27 28 Fluorescence spectra of L-Cu 2+ upon the addition of Cr 3+ in methanol: drinking water (4:1) system. Fluorescence spectra of L upon the addition of Cu 2+ in methanol: tap water (4:1) system. Comparison of detection limits of L + Cu 2+ + Cr 3+ in different solvent systems Figure S23 Figure S24 Table S3 29 Detection limit of L-Cu 2+ for Cr 3+ in drinking water Figure S25 3 Detection limit of L-Cu 2+ for Cr 3+ in tap water Figure S26 31 Reference S2

General information: Preparation of the test solution: UV-vis and fluorescence titrations were performed using stock solutions of higher concentration to avoid dilution error. The ligand (L) stock solutions preparation: Ligand (3.9 mg,.1 mmol) was dissolved in 1 ml methanol to get 1. mm stock solution, which was then diluted further using a mixture of methanol:h 2 O (4:1, v/v) buffered with HEPES (1 mm), ph = 7.2 to 1 µm solution to perform relevant experiments. Stock solutions of other metals, including Al 3+, Fe 3+, Cu 2+, Cd 2+, Zn 2+, Na +, Mg 2+, Hg 2+, Co 2+, Pb 2+, Ni 2+, Ag +, Mn 2+ and Cr 3+ were prepared in DI H 2 O to get 1. mm stock solution, which was then diluted to 1 µm solution using DI water to perform relevant experiments. UV-vis and fluorescence titrations: Each time, a freshly prepared 3 ml stock solution of probe L was taken in the quartz cuvette (path length 1 cm), and the desired amount of metal ions was added with a microsyringe. All measurements were taken at room temperature at 289 nm excitation wavelength by keeping 5 nm as excitation and 5 nm as emission slit width respectively. Table S1: Comparison of potential of probe L with other reported Cr 3+ -specific/selective molecular probes. Sensitive dye working range Detection limit Ref 1,8-naphthalimide and rhodamine 1- µm 1 Spirobenzopyran derivative 1. 1 5 M 6.9 µm 2 Ferrocene and pyrene 2.85 1 6 M to 5. 1 4 M, in H 2 O 1 µm 3 2-(5,6-dihydro-benzo- [4,5]imidazo[1,2-c]quinazolin-6-yl)- quinolin-8-ol 3.6 1-7 mol L -1 3.6 x 1-7 mol L -1 4 4,13-diaza-18-crown-6 ether 1.3 x 1 4 M -1.144 µm 5 1,8-naphthalimide and rhodamine moieties 3 nm to.14 nm 6 S3

2-(2'-hydroxyphenyl) benzoxazole (HBO) 8 mm 3 µm.2 µm (Cr 3+ ) and.5 µm (Al 3+ ) 7 (1, 1-(4-cyano-phenyl)-3-(4- dimethylamino-phenyl)-thiourea)) 5.56 x1 4 M -1 8.18 x 1-7 M 8 Cyclometalated Ir(III) complexes 1.93 1 1 M 1 s 1, 9 Table S2. Crystal data and structure refinement for L - Cu +2. 1 Identification code 2 Empirical formula C 8.5 H 19 Cu 2 N 11 O 16.5 3 Formula weight 1621.87 4 Temperature 15.(1) K 5 Crystal system, Space group Monoclinic, C2 6 Unit cell dimension a=31.769(9) Å, α=9. b=8.9771(2) Å, β=11.34(3) c=32.5469(1),å γ=9. 7 Volume/Å 3 873.4(4) 8 Z, Calculated density (ρ) 4, 1.238mg/m 3 9 Absorption coefficient 1.157 m/mm -1 1 F() 3436. 11 Theta range for data collection 5.62 to 133.86 12 Limiting indices -37 h 3, -1 k 1, -38 l 38 13 Reflections collected / unique 21846/ 12234[R(int) =.1167] 14 Absorption correction 15 Data/restraints/parameters 12234/1/119 16 Goodness of fit on F 2 1.49 17 Final R indexes [I>=2σ (I)] R 1 =.1134, wr 2 =.3251 18 R indexes [all data] R 1 =.1272, wr 2 =.3393 19 Largest diff. peak/hole / eå -3 1.69/-.71 2 Flack parameter.7(5) S4

Figure S1. 1 H NMR spectra of Ligand (L) in methanol-d 4. S5

Figure S2. 13 C-NMR spectra of Ligand (L) in methanol-d 4. Figure S3. HRMS spectra of Ligand (L) in acetonitrile. S6

Figure S4. The ORTEP diagram of [CuL 2 (H 2 O)] complex. Figure S5. UV-vis spectra of probe L (1 µm) in methanol: H 2 O (4:1, v/v) buffered with HEPES (1 mm, ph = 7.2). S7

5 4 3 1 3 32 34 Wavelength/nm Figure S6. Fluorescence emission spectra of probe L (2 µm) in Methanol: H 2 O (4:1, v/v) buffered with HEPES (1 mm, ph = 7.2) excitation at 289 nm. Emission intensity(a.u) 1 2 3 4 5 6 7 8 9 1 11 12 13 ph values of L Figure S7. Fluorescence response of L (1 µm) in methanol: H 2 O (4:1, v/v) buffered with HEPES (1 mm) at different ph (λ ex = 289 nm). S8

Figure S8. UV-vis spectra of probe L (1 µm) in methanol: H 2 O (4:1, v/v) buffered with HEPES (1 mm), ph = 7.2 upon the addition of increasing quantities of Cu 2+ ( to 4. 1 3 pm). Compound 2 µm + Cr 3+ ( 8 nm) Compound 2 µm Compound 2 µm + Cr 3+ ( 2 nm).4 Compound 2 µm + Cr 3+ ( 4 nm) Compound 2 µm + Cr 3+ ( 1 µm) Absorbance.2. 25 26 27 28 29 3 31 32 Wavelength/nm Figure S9. UV-vis spectra of probe L (2 µm) in methanol: H 2 O (4:1, v/v) buffered with HEPES (1 mm), ph = 7.2 upon the addition of increasing quantities of Cr 3+ ( to 1. µm). S9

L L + Other metal ion L + Other metal ion + Cu 2+ 4 3 1 Fe 3+ Al 3+ Cd 2+ Pb 2+ Na + Mg 2+ Ni 2+ Cr 3+ Co 2+ Hg 2+ Zn 2+ Figure S1. Fluorescence emission intensity of L (2 µm) towards Cu 2+ (1 µm) in methanol: H 2 O (4:1, v/v) buffered with HEPES(1 mm), ph = 7.2 (at λ ex 289 nm) in the presence of Al 3+, Fe 3+, Cd 2+, Zn 2+, Na +, Mg 2+, Hg 2+, Co 2+, Pb 2+, Ni 2+, Ag +, Mn 2+ and Cr 3+ (1 µm). 5 4 3 1 (a) Ligand (2 µm) L +.333 µm Cu 2+ L +.666 µm Cu 2+ L + 1 µm Cu 2+ L + 1.333 µm Cu 2+ L + 1.666 µm Cu 2+ L + 2 µm Cu 2+ 3 31 32 33 34 35 Wavelength/nm 4 3 1 (b) 17.9% 34.1% 48% 56.9%.333.666 1 1.333 Concentration of Cu 2+ ion in µm Figure S11. a) Fluorescence spectra of L (2 µm) in methanol: buffer (4:1, v/v) excitation at 289 nm as a function of the concentration of Cu 2+, b) fluorescence intensity of L (2 µm) in methanol: buffer (4:1, v/v) excitation at 289 nm as a function of the concentration of Cu 2+. S1

5 4 3 1 (a) Ligand (2 µm) L +.333 µm Cu 2+ L +.666 µm Cu 2+ L + 1 µm Cu 2+ L + 1.333 µm Cu 2+ L + 1.666 µm Cu 2+ L + 2 µm Cu 2+ 3 31 32 33 34 35 W avelength/nm 45 4 35 3 25 15 (b) 1.2..4.8 1.2 1.6 2. Concentration of metal in µm Figure S12. (a) Fluorescence spectra of L (2 µm) in methanol: buffer water (4:1, v/v) (at λex 289 nm) upon the addition of increasing quantities of Cu 2+ ( to 2 µm), (b) Change of fluorescence intensity of L upon addition of Cu 2+. Absorbance.3.25.2.15.1.5 Compound 1 µm + Cu 2+ ( 5 µm) Compound 1 µm + Cu 2+ ( 5 µm) + Cr 3+ (5 µm) Compound 1 µm + Cu 2+ ( 5 µm) + Cr 3+ (2.5 µm) Compound 1 µm + Cu 2+ ( 5 µm) + Cr 3+ (1 µm) Compound 1 µm + Cu 2+ ( 5 µm) + Cr 3+ (7.5 µm) Compound 1 µm + Cu 2+ ( 5 µm) + Cr 3+ (12.5 µm). 24 27 3 33 36 Wavelength/nm Figure S13. The UV-vis spectra of L-Cu 2+ (5 µm) in methanol: H 2 O (4:1, v/v) buffered with HEPES (1 mm), ph = 7.2 upon the addition of increasing quantities of Cr 3+ ( to 12.5 µm). S11

5 4 3 1 (a) Compound (2 µm) Compound (2 µm) + Cu 2+ (1 µm) + Cr 3+ (-1 µm) Compound (2 µm) + Cu 2+ (1µM) 3 32 34 36 Wavelength/nm % Increment of Fluorescence Intensity 1 8 6 4 2 (b) 1.3% 9.42% 9% 7.9% 6.5% 4 pm 5 pm 9 pm 4 pm 6 pm Concentration of Cr 3+ Figure S14. a) Fluorescence spectra of probe L-Cu 2+ (1 µm) in methanol: buffer (1:1, v/v) (at λ ex 289 nm) upon the addition of increasing quantities of Cr 3+ ( to 1 µm), b) % increment of fluorescence intensity of L-Cu 2+ (1 µm) in methanol: buffer (1:1, v/v) excitation at 289 nm as a function of the concentration of Cr 3+. S12

Figure S15. Fluorescence life time spectra of L, L-Cu 2+, L+Cu 2+ +Cr 3+ and L-Cr 3+ in methanol: H 2 O (4:1, v/v) buffered with HEPES (1 mm), ph = 7.2. Binding constant calculation Methods for association or stability constant calculation: Binding properties of L- Cu 2+ /Cr 3+ complexes were determined by fluorescence titrations. All the measurements were performed by titrating L with Cu 2+ and Cr 3+ metal ions in H 2 O (HEPES buffered, ph ~7.2) / MeOH (1:4) at 25 C. Initial concentrations of the L and metals were 2 1-6 M and 1-6 M, respectively. Each titration was performed by several measurements with varying metal ion concentrations in order to avoid dilution error, and the association constants were calculated using Benesi-Hildebrand method. 2 15 Equation y = a + b*x.98821 Adj. R-Square Value Standard Error B Intercept -21.26249 1.63313 B Slope 32.1237 1.7599 (F α - F /F x -F ) 1 5.7.8.9 1. 1.1 1.2 1.3 (1/C) 1/2 Figure S16. Benesi-Hildebrand method for the calculation of binding constant for L+Cu 2+ upon gradual addition of Cu 2+ solution to a L solution, Excitation at 289 nm in methanol: H 2 O (4:1, v/v) buffered with HEPES (1 mm), ph = 7.2. S13

22 2 18 Equation y = a + b Adj. R-Squa.97952 Value Standard Err B Intercept 1.95823.557 B Slope 14.5267.69931 (F α - F /F x -F ) 16 14 12 1 8 6.4.6.8 1. 1.2 (1/C) 1/2 Figure S17: Benesi-Hildebrand method for the calculation of binding constant for L+Cr 3+ upon gradual addition of Cr 3+ solution to a L-Cu 2+ solution, Excitation at 289 nm in methanol: H 2 O (4:1, v/v) buffered with HEPES (1 mm), ph = 7.2. Fluorescence Itensity(a.u.) 24 22 18 16 X = L + Cu 2+ Y = L + other metal ion + Cu 2+ Z = L + other metal ion + Cu 2+ + Cr 3+ Na + Mg 2+ Cd 2+ Pb 2+ Ni 2+ Hg 2+ Fe 3+ Co 2+ Al 3+ Zn 2+ Mn 2+ Ag + Cr 3+ Figure S18. Fluorescence emission intensity of L-Cu 2+ (1 µm) towards Cr +3 (1 nm) in methanol: H 2 O (4:1, v/v) buffered with HEPES(1 mm), ph = 7.2 (at λ ex 289 nm) in the presence of Al 3+, Fe 3+, Cd 2+, Zn 2+, Na +, Mg +2, Hg 2+, Co 2+, Pb 2+, Mn 2+, Ni + and Ag + (1 nm). S14

16 12 8 4 3 31 32 33 34 Wavelength/nm Ligand (L) with Cu 2+ L+ Cu 2+ +.333 pm Cr 3+ L+ Cu 2+ +.666 pm Cr 3+ L+ Cu 2+ + 1 pm Cr 3+ L+ Cu 2+ + 1.333 pm Cr 3+ L+ Cu 2+ + 2.333 pm Cr 3+ L+ Cu 2+ + 3.333 pm Cr 3+ L+ Cu 2+ + 4.333 pm Cr 3+ L+ Cu 2+ + 5.333 pm Cr 3+ L+ Cu 2+ + 6.333 pm Cr 3+ Figure S19. Fluorescence titration spectra of L-Cu 2+ (1 µm) in methanol: water (4:1, v/v) buffered with HEPES (1 mm), ph = 7.2 (at λ ex 289 nm) in the presence of Cr 3+ ( to 6.333 pm). Figure S2. Job plots for L-Cu +2 complex (λ ex =289 nm). S15

Figure S21. Job plots for L-Cr +3 complex (λ ex =289 nm). 2L+Cr +3 +2CH 3OH+2DMF+ Li+LiOH+H + 2L+Cr +3 2L+Cr +3 +CH 3OH+DMF+Li +H 2O+H + Figure S22. HRMS spectra of L-Cr 3+ in acetonitrile. S16

Detection of Cr 3+ ion in real samples: Drinking water, river water and tap water were used as real samples for analysis of Cr 3+ ion. These real samples used as solvents to record the fluorescence spectra. The detection procedure for drinking water, river water and tap water is the same as that used above. We are in the process of collecting various real-world samples which contain Cr 3+ ion and would like to apply our probe in future to detect the presence of those metal ions. 3 25 15 3 35 31 315 32 325 33 Wavelength/nm L + Cu 2+ L+ Cu 2+ +.333 pm Cr 3+ L+ Cu 2+ +.666 pm Cr 3+ L+ Cu 2+ + 1 pm Cr 3+ L+ Cu 2+ + 1.333 pm Cr 3+ L+ Cu 2+ + 2 pm Cr 3+ L+ Cu 2+ + 2.666 pm Cr 3+ L+ Cu 2+ + 3 pm Cr 3+ L+ Cu 2+ + 4 pm Cr 3+ L+ Cu 2+ + 5 pm Cr 3+ L+ Cu 2+ + 6 pm Cr 3+ L+ Cu 2+ + 7 pm Cr 3+ Figure S23. Fluorescence titration of L-Cu 2+ (1 µm) in methanol: drinking water (4:1, v/v) buffered with HEPES (1 mm), ph = 7.2 (at λ ex 289 nm) in the presence of Cr 3+ ( to 7 pm). S17

25 15 1 5 L + Cu 2+ L+ Cu 2+ +.333 pm Cr 3+ L+ Cu 2+ +.666 pm Cr 3+ L+ Cu 2+ + 1 pm Cr 3+ L+ Cu 2+ + 1.666 pm Cr 3+ L+ Cu 2+ + 2.666 pm Cr 3+ L+ Cu 2+ + 3.666 pm Cr 3+ L+ Cu 2+ + 4.666 pm Cr 3+ L+ Cu 2+ + 6.666 pm Cr 3+ 3 32 34 36 Wavelength/nm Figure S24. Fluorescence titration of L-Cu 2+ (1 µm) in methanol: tap water (4:1, v/v) (at λ ex 289 nm) buffered with HEPES (1 mm), ph = 7.2 in the presence of Cr 3+ ( to 6.666 pm). Table S3. Comparison of detection limits of L + Cu 2+ + Cr 3+ in different solvent systems. c Types of water Detection Limit 1 Buffer.666 pm 2 Drinking Water.666 pm 3 Tap Water 2.666 pm 4 River Water 2 pm S18

3 25 15 1 5 1.77% 13.33% 15.75% 18.29% 2.12%.333.666 1 1.333 2 Concentration of Cr 3+ ion in pm Figure S25. Fluorescence intensity of L-Cu 2+ (1 µm) in methanol: drinking water (4:1, v/v) buffered with HEPES (1 mm), ph = 7.2 excitation at 289 nm as a function of the concentration of Cr 3+. 25 15 1 5 4.1% 5.6% 6.6% 9.17% 1% 11.3%.333.666 1 1.666 2.666 3.666 Concentration of Cr 3+ ion in pm Figure S26. Fluorescence intensity of L-Cu 2+ (1 µm) in methanol: tap water (4:1, v/v) buffered with HEPES (1 mm), ph = 7.2 excitation at 289 nm as a function of the concentration of Cr 3+. S19

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