Barun Kumar Datta, Chirantan Kar, Gopal Das*

Supporting information

A fluorescent naphthalene based benzene tripod for the selective recognition of fluoride in physiological condition

Barun Kumar Datta, Chirantan Kar, Gopal Das*

Department of Chemistry, Indian Institute of Technology Guwahati, Assam 781 039, India.

Experimental

Materials and methods

All reagents were obtained from commercial sources and used as received. Solvents were distilled freshly following standard procedures.

Instrumentation

Fluorescence measurements were conducted on a Horiba Fluoromax-4 spectrofluorometer using 10 mm path length quartz cuvettes with a slit width of 5 nm at 298 K. All the mass spectra were obtained using Agilent Technologies 6520 Accurate mass spectrometer. NMR spectra were recorded on a Varian FT-400 MHz instrument. The chemical shifts were recorded in parts per million (ppm) on the scale. The following abbreviations are used to describe spin multiplicities in 1H NMR spectra: s = singlet; d = doublet; t = triplet; m = multiplet. Elemental analyses were performed with a Perkin-Elmer 2400 elemental analyzer.

Synthesis of 1,3,5-Tris(bromomethyl)-2,4,6-trimethylbenzene (1):

The compound was prepared by literature method. To a mixture of paraformaldehyde (2 g; 0.066 mol), and trimethylbenzene(1.0 g; 0.01 mol) in 100 mL of HBr/AcOH (30 wt %) zinc bromide (2.25 g; 0.01mol) was slowly added at room temperature. The mixture was heated to 90 °C for 16.5 h, during which time white crystals were formed. The reaction was cooled to room temperature, and the white solid was filtered off, washed with water, and dried under vacuum overnight to give 1 as a white solid. Yield 3.9 g (97%). Mp =185-187oC; 1H NMR (400 MHz, CDCl3): δ 2.46 (s, 9H, -CH3), 4.57(s, 6H, -CH2Br).

Synthesis of compound 2:

To a mixture of p-nitrophenol (1.04g 7.48mmol) and K2CO3 (1.05 g, 7.6mmol) in acetone (130mL) was added 1,3,5-tris(bromomethyl)-2,4,6-trimethylbenzene (1g, 2.5mmol) at room temperature. The reaction mixture was stirred at room temperature for 17 h. The solvent was removed under reduced pressure, and the residue was washed with water several times to give 2 as an off white solid, dried in vacuum. Yield 1.35g (95%).Mp 212–214 oC; 1H NMR (400 MHz, CDCl3) 2.45 (s, 9H), 5.22 (s, 6H), 7.09 (d,J=9.2 Hz, 6H), 8.26 (d, J=9.6Hz, 6H), 13C NMR (100 MHz, CDCl3) 16.2, 65.8, 102.0, 114.7, 126.2, 131.2, 140.1,166.6; IR KBr (cm-1) 2920, 2860, 1730, 1590, 1510, 1340, 1250; HRMS (positive mode, ESI, [M+H+]+) calcd for C30H28N3O9: 574.1826 found 574.1342.

Synthesis of compound 3:

Hydrazine monohydrate (4.0 mL) was added drop wise to the mixture of compound 2 (1.35 g) and Pd/C 10 % (.15g, cat ) in methanol (50 ml).After refluxing for 12 hours, the solution was filtered through celite to remove Pd/C. Evaporation of the solvent gave 3 as a white crystalline solid,dried under vaccum. Yield1g (88%).Mp170-172oC; 1H NMR (400 MHz, CDCl3) 2.42 (s,9H), 3.42(s,6H), 4.98 (s, 6H), 6.64 (d, J=8.8 Hz,6H), 6.84 (d, J=8.8 Hz, 6H), 13C NMR (100 MHz, CDCl3) d 15.9, 65.9, 116.0, 116.5, 132.2, 139.1,140.4, 152.5; IR KBr (cm-1) 3444, 3350, 2930, 1630, 1510, 1370,1230; HRMS (positive mode, ESI, [M+H+]+) calcd for C30H34N3O3:484.2600, found: 484.2555.

Synthesis of compound L1:

Compound 3 (1g) and 2-hydroxy-naphthaldehyde (1.1 g) were dissolved in 50 ml methanol and refluxed overnight. During this time a yellow precipitate formed. The solution was cooled to room temperature .The precipitate was filtered out, washed with methanol several times and dried over vacuum to gave L1 as a yellow powder. Yield 1.5 g (77%) Mp180-182oC; 1H NMR (400 MHz, DMSO-d6) 2.37 (s, 9H), 5.15 (s, 6H), 7.02 (d, J=9.2 Hz, 6H), 7.19 (d, J=8.4 Hz, 6H), 7.34(t, J=7.2Hz, 3H), 7.54 (t,J=7.6 Hz, 3H), 7.65 (d, J=8.8 Hz, 3H), 7.79 (d, J=8 Hz, 3H), 7.90 (d, J=8 Hz,6H ), 8.48 (d, J=8.4 Hz, 3H), 9.64(s, 3H);13C NMR (100 MHz, DMSO-d6) d 15.5,65.2,96.7,108.6,115.5,120.3,122.0,123.3,126.7,128.0,129.0,131.3,133.0,136.1,137.6,138.8,154.5,157.8,169.2; HRMS (positive mode, ESI, [M+H+]+) calcd for C63H52N3O6:946.3811, found: 946.3995.

General method for measurements of photophysical properties

For fluorescence titrations stock solution of ligands L1was prepared (c = 2 mM) in DMSO. For checking the relative, but qualitative, binding affinity of individual cations towards the reagent L1, the effective anion concentration in Acetonitrile/ aqueous HEPPES buffer (2:3, v/v) was maintained at 25.0 × 10-6 M, while that for the receptor L1 was maintained at 1.0 × 10-6 M. The solution pH was found to be 7.4.The solutions of guest anions were prepared in H2O in the order of 10-3 M. Working solutions of the ligandsand metal ions were prepared from the stock solutions. Excitation was carried out at 360 nm for boththe ligandswith 5 nm excitation and 5 nm emissions slit widths.

Figure S1: 1HNMR spectra of compound 2 in CDCl3.

Figure S2: 1HNMR spectra of compound 3 in CDCl3.

Figure S3: 1HNMR spectra of L1 in DMSO-d6.

Figure S4: 13C NMR spectra of compound 2 in CDCl3.

Figure S5: 13C NMR spectra of compound 3 in CDCl3.

Figure S6: 13C NMR spectra of L1 in DMSO-d6.

Figure S7: 13C NMR spectra of compound L2 in CDCl3.

Figure S8: Mass spectrum of L1; m/zcalcd. for [L1+H]+ is 946.3811 found 946.3995.

Figure S9: Mass spectrum of L1-Al3+; m/zcalcd. for[L1-2H++Al3+]+ calcd = 970.3437 found 970.3619.

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