Silver Nanoparticles Functionalised with a Luminescent Iridium Complex: Phophorescent

Silver nanoparticles functionalised with a luminescent iridium complex: phophorescent hybrid materials

Andrew J. Hallett, Paul Christian, Matthew Broomfield and Simon J. A. Pope

Experimental

The preparation, purification and reactions of the complexes described were carried out using Schlenk techniques under an atmosphere of dry nitrogen. Reagents were purchased from commercial suppliers and used without further purification. The compounds1-aminohexane-6-thioacetate.CF3CO2H1,[1] 4-methyl-2,2′-bipyridine-4′-carboxylic acid[2]and [(ppy)2Ir(μ-Cl)2Ir(ppy)2][3]were prepared by published methods.

1H and 13C-{1H} NMR spectra and were run on NMR-FT Bruker 400 and 250 MHz or Jeol 300 spectrometers and were recorded in CDCl3. 1H and 13C-{1H} NMR chemical shifts () were determined relative to internal TMS and are given in ppm. Mass spectra were obtained by the staff of the Chemical Analysis Service of Cardiff University on a Waters LCT Premier XE ESI/APCI mass spectrometer. High resolution accurate mass determinations of the ligands and complexes were performed at the EPSRC National Mass Spectrometry Service at Swansea University. Photophysical data were obtained on a JobinYvon-Horiba Fluorolog spectrometer fitted with a JY TBX picosecond photodetection module. Emisson spectra were uncorrected and excitation spectra were instrument corrected. The pulsed source was a Nano-LED configured for 459 nm output operating at 500 kHz. Luminescence lifetimes were obtained using the JobinYvon-Horiba FluoroHub single photon counting module.

Data collection and processing

Diffraction data for Ir-L1 were collected on a Nonius KappaCCD using graphite-monochromated Mo-K radiation (λ = 0.71073 Å) at 150 K. Software package Apex 2 (v2.1) was used for the data integration, scaling and absorption correction.

Structure analysis and refinement

The structure was solved by direct methods using SHELXS-97 and was completed by iterative cycles of F-syntheses and full-matrix least squares refinement. All refinements were against F2 and used SHELX-97.[4]

TEM imaging

TEM images were collected by evaporation of a suspension of the nanomaterial in MeOH onto a carbon coated copper grid. Images were generated using a Philips CM200 TEM fitted with a LaB6 filament working at 200 kV.

Synthesis

L1

4-Methyl-2,2′-bipyridine-4′-carboxylic acid (0.120 g, 0.56 mmol) was refluxed in SOCl2 (5 ml) with 1 drop of dmf as a catalyst for 3 hours. The excess SOCl2 was removed in vacuo and the product dissolved in CH2Cl2 (5 ml). 1 (0.145 g, 0.50 mmol) and EtNiPr2 (2 ml, excess) in CH2Cl2 (5 ml) were added dropwise and the mixture stirred at room temp overnight. The product was washed with water (2 x 20 ml) and brine (20 ml), dried over MgSO4 and filtered. The solvent was removed in vacuo to give a light brown oil. Yield = 0.173 g (93 %). 1H NMR (400 MHz, CDCl3) H = 8.67 (1H, d, 3JHH = 4.9 Hz), 8.54 (1H, s), 8.41 (1H, d, 3JHH = 4.9 Hz), 8.15 (1H, s), 7.68 (1H, d, 3JHH = 4.7 Hz), 7.07 (2H, m), 3.35 (2H, m), 2.50 (2H, m), 2.35 (3H, s), 2.23 (3H, s), 1.42-1.58 (4H, m), 1.18-1.32 (4H, m) ppm. 13C-{1H} NMR (101 MHz, CDCl3) C = 195.2, 164.7, 155.8, 154.1, 148.9, 147.8, 147.4, 141.9, 124.2, 121.1, 120.7, 116.7, 39.1, 29.6, 28.3, 28.2, 27.9, 27.3, 25.4, 20.2 ppm.IR: (KBr, cm-1) υ = 1670(s). ES MS found m/z = 372.2 and 394.2, calculated m/z372.2and 394.2 for [M+H]+and [M+Na]+ respectively. HR MS found m/z372.1739, calculated m/z372.1740 for [C20H26O2N3S]+.

[Ir(L1)(ppy)2][PF6][Ir-L1]+

[(ppy)2Ir(μ-Cl)2Ir(ppy)2] (0.080 g, 0.07 mmol) and L1 (0.059 g, 0.16 mmol) in 2-methoxyethanol (10 ml) were heated at 80 °C for 16 hours. The solvent was then removed in vacuo and the crude product dissolved in MeCN (3 ml). NH4PF6 (0.2 g) in water (1 ml) was then added and stirred for 5 mins. The product extracted into CH2Cl2 (20 ml) and washed with water (2 x 20 ml) and brine (20 ml). The organic phase was then dried over MgSO4, filtered and the solvent lowered in volume in vacuo. The product was precipitated as an orange powder by the slow addition of Et2O. Yield = 0.138 g (91 %).1H NMR (250 MHz, CDCl3) H = 8.70 (1H, s), 8.57 (1H, s), 7.94 (1H, d, 3JHH = 5.7 Hz), 7.81-7.87 (2H, m), 7.78 (1H, d, 3JHH = 5.7 Hz), 7.52-7.64 (5H, m), 7.47 (1H, d, 3JHH = 5.8 Hz), 7.39 (1H, d, 3JHH = 5.6 Hz), 7.14 (1H, d, 3JHH = 5.6 Hz), 6.85-7.01 (5H, m), 6.22 (2H, d, 3JHH = 7.5 Hz), 3.41 (2H, m), 2.79 (2H, m), 2.56 (3H, s), 2.24 (3H, s), 1.25-1.66 (8H, m) ppm.IR: (KBr, cm-1) υ = 1672(s). EI MS found m/z = 872.3; calculated m/z872.1 for [M-PF6]+. HR MS found m/z872.2589, calculated m/z872.2605 for [C42H41O2N5191IrS]+.

Silver nanoparticle synthesis

Silver nanoparticles were prepared by reducing AgNO3 with NaBH4 in the presence of the capping agent MPEGSH in MeOH. The particles were found to have an average diameter of 4.7 nm. The solid contained approximately 49 % silver by mass, the rest being the capping agent.[5]

Silver nanoparticle conjugates

Ir-L1-SNP

In a flask protected from sunlight Ir-L1 (0.023 g, 0.02 mmol) and silver nanoparticles (0.008 g, 4.7 nm, 49 % Ag by weight) were stirred in MeOH (2 ml) for 24 hours. The solvent was removed in vacuo at room temp. The product was purified by column chromatography (silica CH2Cl2/MeOH 9:1). The crude mixture was added in CH2Cl2/MeOH 9:1 and eluted with the same mixture to give unreacted Ir-L1 (as confirmed by 1H NMR and luminescence spectroscopy). The Ir-L1-SNP conjugate was eluted with CH2Cl2/MeOH (1:1) to give a dark brown-red product.

Crystallagraphic data

Table 1 Crystal and refinement data for [Ir(ppy)2(L1)][PF6]Ir-L1.a,b

[Ir(ppy)2L1][PF6]
Formula / C42H41F6IrN5O2PS
Formula weight / 1017.03
Temperature / K / 150(2)
Wavelength / Å / 0.71073
Crystal system / Triclinic
Space group / P-1
a/Å / 8.9730(2)
b/Å / 19.6290(4)
c/Å / 24.5830(6)
/ / 71.5020(10)
/ / 83.2510(10)
/ / 88.3390(10)
Volume/Å3 / 4077.52(16)
Z / 4
F000 / 2024
/mm-1 / 3.436
Reflections collected / 21565
Independent reflections (Rint) / 13386(0.0572)
Final R1 [I>2σ(I)]: R1, wR2 / 0.0622, 0.1272

aH atoms were positioned geometrically and refined using a riding model with U(iso) = 1.2 or 1.5 times U(eq) for the atom they are bonded to.bThere are to independent hexafluorophosphate anions which, together with the flexible chains of the complex, are disordered. Refinement of the disorder has been performed with geometrical restraints using PART and SAME instructions in
SHELX. Atoms in close proximity have been refined with identical or similar displacement parameters using SIMU and ISOR instructions.

Table 2 Selected bond lengths (Å) and angles (°) for [Ir(ppy)2(L1)][PF6]Ir-L1.

Bond length / Å / Bond angle / °
Ir(1)-N(1) / 2.141(7) / N(1)-Ir(1)-N(2) / 76.3(3)
Ir(1)-N(2) / 2.135(8) / N(4)-Ir(1)-N(5) / 172.5(3)
Ir(1)-N(4) / 2.038(8) / N(1)-Ir(1)-C(31) / 172.3(3)
Ir(1)-N(5) / 2.030(8) / N(2)-Ir(1)-C(42) / 174.6(3)
Ir(1)-C(31) / 2.011(9)
Ir(1)-C(42) / 2.024(10)

[1]A. J. Hallett, P. Christian, J. E. Jones and S. J. A. Pope, Chem. Commun.(2009)4278-4280.

[2]D.G. McCafferty, B. M. Bishop, C. G. Wall, S. G. Hughes, S. L. Mecklenberg, T. J. Meyer and Bruce W. Erickson, Tetrahedron 51(1995) 1093-1106.

[3]M. Nonoyama, Bull. Chem. Soc. Jpn. 47(1974)767-768.

[4]SHELXL-PC Package. Bruker Analytical X-ray Systems: Madison, WI (1998).

[5]P. Christian, M. Bromfield. J. Mater. Chem. 20 (2010) 1135-1139.