Supporting Information

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1 Supporting Information For A Highly Sensitive ESIPT Based Ratiometric Fluorescence Sensor for Selective Detection of Al 3+ Sanghamitra Sinha, Bijit Chowdhury and Pradyut Ghosh* Department of Inorganic Chemistry, Indian Association for the Cultivation of Science, 2A & 2B Raja S. C. Mullick Road, Kolkata , India. icpg@iacs.res.in Contents Page no. 1. Figure S1: 1 H-NMR spectrum of 1H in DMSO-d Figure S2: : 1 H- 1 H COSY-NMR spectrum of 1H in DMSO-d Figure S3: 13 C-NMR spectrum of 1H in DMSO-d Figure S4: : 1 H- DEPT-135 HSQC-NMR spectrum of 1H in DMSO-d Figure S5: ESI-MS of 1H 4 6. Scheme S1. Synthetic scheme of 1 Me 5 7. Figure S6: 1 H-NMR spectrum of 1 Me in DMSO-d Figure S7: ESI-MS of 1 Me 6 9. Figure S8: 3-D crystal packing of 1H (ethyl acetate) Table S1: List of crystallographic parameter details of ligand 1H Figure S9: UV-vis and PL spectra of 1 Me and in presence of Al Chart S1: Schematic representation of ESIPT mechanism Figure S10: Qualitative UV-vis spectra of 1H in acetonitrile Figure S11: Fluorescence titration profile for 1H (2.5 µm) with Cr Figure S12: Plot for quantum yield measurement Figure S13: UV-vis titration data of 1H with Al 3+ in acetonitrile Figure S14: Fluorescence Job s plot for 1H (2.5 µm) with Al 3+ in acetonitrile Figure S15: Selectivity and detection limit of 1H for Al 3+ in acetonitrile Table S2, S3 and Figure S16. Time-resolved luminescence data for 1H Figure S17: UV-vis and fluorescence spectra of 1H in H 2 O/acetonitrile (9:1 v/v) Figure S18, S19: UV-vis titration and Job s plot for 1H with Al Figure S20: Fluorescence equivalent plot for 1H with Al Figure S21: Benesi-Hildebrand plot and detection limit of 1H with Al Figure S22: Fluorescence decay profile of 1H with Al 3+ in H 2 O/acetonitrile (9:1 v/v) Figure S23. 1 H-NMR titration spectra of 1H with Al 3+ in D 2 O/CD 3 CN (1:1 v/v) Figure S24. 1 H-NMR spectrum of [Al(1)(OH)] 2+ 2 in DMSO-d Figure S25 and S26: ESI-MS spectra of the Al 3+ adduct of 1H Figure S27: DFT optimized structures of S 0 and S 1 states of [Al(1)(OH)] Figure S28: Selected MOs of 1H(enol), 1H(keto) and [Al(1)(OH)] Figure S29. Theoretical/experimental UV-vis spectra of 1H and [Al(1)(OH)] Table S4. Main calculated optical transitions for 1H and [Al(1)(OH)] Table S5. Main geometric parameters for S 0 and S 1 states of [Al(1)(OH)] Table S6: Cartesian coordinates of 1H(enol), 1H(keto) and [Al(1)(OH)]

2 Figure S1: 1 H-NMR (300 MHz) spectrum of 1H in DMSO-d 6. 2

3 Figure S2: 1 H- 1 H COSY-NMR (400 MHz) spectrum of 1H in DMSO-d 6. Figure S3: 13 C-NMR (100 MHz) spectrum of 1H in DMSO-d 6. 3

4 Figure S4: 1 H-DEPT-135 HSQC-NMR (400 MHz) spectrum of 1H in DMSOd 6. Figure S5: ESI-MS spectrum of 1H. 4

5 Scheme S1. Synthetic scheme of 1 Me. Figure S6: 1 H-NMR (500 MHz) spectrum of 1 Me in DMSO-d 6. 5

6 Figure S7: ESI-MS spectrum of 1 Me. Figure S8: A slice of three-dimensional (3-D) crystal packing of 1H obtained from ethyl acetate, along the crystallographic c axis. 6

7 Table S1: List of crystallographic parameter details of ligand 1H. Compound reference 1H Chemical formula C 29 H 31 N 3 O 3 Formula Mass Crystal system Orthorhombic a/å 20.07(3) b/å (16) c/å 20.36(3) α/ β/ γ/ Unit cell volume/å (12) Temperature/K 150(2) Space group Pbca No. of formula units per unit cell, Z 8 Radiation type MoKα Absorption coefficient, μ/mm No. of reflections measured No. of independent reflections 2661 R int Final R 1 values (I > 2σ(I)) Final wr(f 2 ) values (I > 2σ(I)) Final R 1 values (all data) Final wr(f 2 ) values (all data) Goodness of fit on F CCDC number

8 Figure S9: (a) UV-vis and PL spectra of 1 Me and (b) emission spectral changes of 1 Me in presence of Al 3+ in acetonitrile at room temperature. Chart S1: Schematic representation of ESIPT mechanism. Figure S10: Changes in absorption spectrum of 1H (20 µm) upon addition of various metal ions (10 equiv) in acetonitrile at room temperature. 8

9 Figure S11: Fluorescence titration profile for 1H (2.5 µm) with Cr 3+ acetonitrile at room temperature. in Figure S12: Plot of integrated emission intensity versus absorbance for calculation of quantum yield (ɸ f ) of 1H and its Al 3+ adduct in acetonitrile using quinine sulphate as standard (Considering the ɸ f of quinine sulphate in 0.1M H 2 SO 4 as 0.55 when the excitation wavelength is 366 nm). 9

10 Figure S13: (a) An equivalent plot from UV-vis titration data and (b) Jobs plot of 1H (20 µm) with Al 3+ (20 µm) in acetonitrile at room temperature. Figure S14. Fluorescence Jobs plot for 1H (2.5 µm) with Al 3+ (2.5 µm) in acetonitrile at room temperature. 10

11 Figure S15: (a) Selectivity graph of 1H with Al 3+ in presence of other metal ions in acetonitrile (λ em = 412 nm for Al 3+, Cr 3+, In 3+ and 445 nm for other metal ions). Orange bars represent the fluorescence intensities of 1H in presence of all metal ions (10 equiv) and green bars correspond to the same in presence of all metal ions and Al 3+. Codes used: (1) Only 1H (2) Mg 2+ (3) Ni 2+ (4) Mn 2+ (5) Cd 2+ (6) Pb 2+ (7) Zn 2+ (8) Co 2+ (9) Fe 3+ (10) Cu + (11) Ag + (12) Hg 2+ (13) In 3+ (14) Cr 3+ (15) Al 3+ and (b) the calibration curve for Al 3+ over the concentration range between 0 and 1.6 μm derived from the PL titration with 1H (2.5 μm) in acetonitrile at room temperature. Table S2: List of lifetimes of 1H (2.5 µm, λ em = 445 nm) and in presence of various metal ions (1 equiv) in acetonitrile. Entry Life Time (ns) Entry Life Time (ns) 1H H + 1 equiv Cd H + 1 equiv Al H + 1 equiv Cr H + 1 equiv Cu H + 1 equiv Fe H + 1 equiv Zn H + 1 equiv Mg H + 1 equiv Co H + 1 equiv Hg H + 1 equiv Ni H + 1 equiv Ag H + 1 equiv Pb

12 Figure S16: Time-resolved luminescence decays of 1H (2.5 µm) (a) at λ em = 412 nm and (b) at λ em = 525 nm, upon addition of increasing amount of Al 3+ in acetonitrile at room temperature. Table S3: List of lifetimes of 1H with increasing amount Al 3+. Equiv of Al 3+ λ em A 1 (%) t 1 (ns) A 2 (%) t 2 (ns) Ʈ avg (ns) χ equiv Al equiv Al equiv Al equiv Al equiv Al

13 Figure S17: UV-vis and fluorescence spectra of 1H, measured in H 2 O/acetonitrile (9:1 v/v) solvent at room temperature (concentrations: 20 µm and 2.5 µm respectively). Figure S18: UV-vis (a) titration profile and (b) corresponding equivalent plot for 1H (20 µm) with Al 3+ in H 2 O/acetonitrile (9:1 v/v) solvent at room temperature. 13

14 Figure S19: UV-vis Job s plot for 1H (20 µm) with Al 3+ H 2 O/acetonitrile (9:1 v/v) solvent at room temperature. (20 µm) in Figure S20: An equivalent plot from fluorescence titration data of 1H (2.5 µm) with Al 3+ in H 2 O/acetonitrile (9:1 v/v) solvent at room temperature. 14

15 Figure S21: (a) Benesi-Hildebrand Plot and (b) calibration curve for fluorescence titration of 1H with Al 3+ in H 2 O/acetonitrile (9:1 v/v) solvent at room temperature. Figure S22: Time-resolved luminescence decays of 1H (λ em = 465 nm) upon addition of increasing amount of Al 3+ in H 2 O/acetonitrile (9:1 v/v) at room temperature. 15

16 Figure S23: Changes in 1 H-NMR spectra (300 MHz) of 1H (8 mm) upon addition of increasing amounts of Al 3+ in D 2 O/CD 3 CN (1:1 v/v) solvent at room temperature. Figure S24: 1 H-NMR spectrum of [Al(1)(OH)] 2 2+ in DMSO-d 6 (300 MHz). 16

17 Figure S25: ESI-MS spectra of the Al 3+ adduct of 1H. Figure S26: Isotopic distribution pattern of (a) [Al(1)O] 2 K + and (b) [Al(1)(OH)] 2 2+ species (in the ESI-MS spectra of the isolated Al 3+ adduct of 1H) with its corresponding simulated pattern. 17

18 Figure S27. Theoretically (DFT B3LYP/6-311G(d); CPCM for acetonitrile) optimized structures of the ground state (S 0 ) and first excited state (S 1 ) of [Al(1)(OH)]

19 Figure S28. Selected MOs of 1H(enol), 1H(keto) and [Al(1)(OH)] 2+ 2 as obtained from the DFT B3LYP/6-311G(d) level of computation using CPCM model to encounter the solvent effect of acetonitrile [isovalue = 0.02]. 19

20 Figure S29: Theoretical (energy calculation by TD-DFT B3LYP/6-311G(d) level of computation (no of states = 26) using CPCM model for acetonitrile) and experimental UV-vis (20 µm) spectra of 1H and [Al(1)(OH)] Table S4. Main calculated optical transitions for 1H and [Al(1)(OH)] Entry Computed vertical excitation Experimentally observed transition Corresponding MOs Oscillator strength (f) Energy (ev) λ ex (nm) Energy (ev) λ ex (nm) 1H (enol) HOMO LUMO HOMO LUMO HOMO LUMO [Al(1)(OH)] HOMO LUMO HOMO-1 LUMO HOMO-1 LUMO

21 Table S5. The main geometric parameters for ground state (S 0 ) and first excited state (S 1 ) of [Al(1)(OH)] Entry Bond angles (degree) Bond lengths (Å) Entry S 0 S 1 S 0 S 1 Al1-O1-Al Al1-O Al1-O3-Al Al1-O O1-Al1-O Al1-O O1-Al2-O Al2-O H1-O1-Al Al2-O H2-O3-Al Al2-O O2-Al1-N O1-H O4-Al2-N O3-H O2-Al1-O N2-H O2-Al1-O N4-H O4-Al2-O N1-Al O4-Al2-O N3-Al N1-Al1-O N1-Al1-O N3-Al2-O N3-Al2-O

22 Table S6: The (x,y,z) Cartesian coordinates of 1H(enol), 1H(keto) and 2+ [Al(1)(OH)] 2 calculated from Gaussian-09 at B3LYP/6-311G(d) computational level using CPCM for acetonitrile. 1H (enol) Atom Coordinates (Angstroms) Coordinates (Angstroms) Atom x y z x y z C C C C C C C H C H C H N H C H C H C H C H O H C H N H C H C H N H C H C H C H C H C H C H C H C H C H

23 1H (keto) Atom Coordinates (Angstroms) Coordinates (Angstroms) Atom x y z x y z C C C C C C C H C H C H O H N H C H C H C H C H C H N H C H C H N H C H C H C H C H C H C H C H C H C H

24 2+ [Al(1)(OH)] 2 Atom Coordinates (Angstroms) Coordinates (Angstroms) Atom x y z x y z C C C C C Al C O C O C Al N C C C C C C C C C O C C N N C C C C C N C C O C C C N C C C C C N C C C C C C C C

25 C H C H C H C H C H C H C H C H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H