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Assembly of Coordination Nanostructures via Ligand Derivatization of Oxide Surfaces Meni Wanunu, Sivan Livne, Alexander Vaskevich, and Israel Rubinstein* Department of Materials and Interfaces, Weizmann Institute of Science, RehoVot 76100, Israel ReceiVed October 14, 2005. In Final Form: December 18, 2005 A scheme is presented for the construction of coordination nanostructures on oxide surfaces (glass, Si/SiO2, quartz), based on application of epoxy-terminated monolayers as anchors for covalent grafting of ligands. Two ligands bearing amine groups were reacted with epoxysilane monolayers on oxide surfaces, providing ligand-terminated substrates. The ligands employed were (i) a pyridine moiety, used for subsequent binding of cobalt tetraphenylporphine (CoTPP), and (ii) deferoxamine (DFX), which contains hydroxamic acid moieties, used for subsequent construction of various Zr4+-based coordination layers. The results suggest that a dense ligand layer was obtained in both cases, allowing the formation of coordination overlayers on the oxide surfaces. The growth of coordinated layers was similar to analogous overlayers assembled on Au substrates, indicating that high ligand coverage is achieved by the epoxyamine surface reaction. Epoxy-based functionalization of oxide substrates is a mild and efficient method for preparing high-quality coordination overlayers. Moreover, the method makes use of commercially available silane and amine reactants, providing the basis for wide application.
Introduction The bottom-up approach for the construction of nanoscale devices on solid substrates is based on stepwise surface modification, generating functional 3D structures with various properties. A key issue in this emerging technology is the functionalization of various inorganic materials (metals, semiconductors, insulators) with organic molecules. Methods allowing the formation of self-assembled monolayers (SAMs) on both metal and oxide-terminated surfaces have been developed,1-5 allowing molecular chemistry and materials technology to merge at the interface. SAMs have been studied predominantly on metal surfaces, due to the availability of sulfur-bearing compounds (mercaptans, sulfides, and disulfides) with a variety of functional groups (carboxylate, amino, hydroxyl, etc.). On the other hand, the common binding groups used for SAMs on oxide surfaces (trihalo- and trialkoxyorganosilanes) are not compatible with the hydroxyl groups of some chemical functionalities (e.g., alcohols, carboxylic acids, hydroxamic acids), due to reactivity with the oxophilic silane. Therefore, the generation of functional SAMs on oxide surfaces [glass, quartz, Si/SiO2, indium-tin oxide (ITO)] proceeds in multiple steps, usually by conversion (chemical, photochemical, or electrochemical) of a preformed silane monolayer.6-8 The ability to apply the same chemistry for bottom-up construction of multilayer films on different substrates may be important for the integration of nanoscale architectures, as discussed by Major and Blanchard9 for covalent multilayer growth. Coordination self-assembly through metal-ion/ligand binding is particularly suited for this purpose, offering mild conditions and versatility. Despite the ubiquitous application of * Corresponding author: tel +972-8-9342678; fax +972-8-9344137; e-mail
[email protected]. (1) Bigelow, W. C.; Pickett, D. L.; W. A. Z. J. Colloid Sci. 1946, 1, 513-538. (2) Polymeropoulos, E. E.; Sagiv, J. J. Chem. Phys. 1978, 69, 1836-1847. (3) Allara, D. L.; Nuzzo, R. G. Langmuir 1985, 1, 45-52. (4) Ulman, A. Chem. ReV. 1996, 96, 1533-1554. (5) Onclin, S.; Ravoo, B. J.; Reinhoudt, D. N. Angew. Chem., Int. Ed. 2005, 44, 6282-6304. (6) Maoz, R.; Cohen, S. R.; Sagiv, J. AdV. Mater. 1999, 11, 55-61. (7) Chechik, V.; Crooks, R. M.; Stirling, C. J. M. AdV. Mater. 2000, 12, 11611171. (8) Flink, S.; van Veggel, F.; Reinhoudt, D. N. J. Phys. Org. Chem. 2001, 14, 407-415. (9) Major, J. S.; Blanchard, G. J. Chem. Mater. 2002, 14, 2574-2581.
coordination chemistry for supramolecular structures in solution,10-12 few groups have described coordination-based assembly on solid substrates primed with ligand groups.13-22 The versatility of constructing coordination multilayers on different types of materials was demonstrated by Mallouk and co-workers,23 who prepared Zr(IV)/alkanebisphosphonate multilayer structures on both Si/SiO2 and Au surfaces. Coordination self-assembly has been a major thrust in our group for a number of years. Our model systems have been prepared on Au surfaces, starting with, for example, a disulfide ligand anchor monolayer, followed by controlled layer-by-layer (LbL) assembly of multilayers through metal-organic coordination.24-27 We have recently shown that our LbL coordination self-assembly scheme can be extended to nanoparticle (NP) multilayers, by using Au NPs functionalized with a bishydrox(10) Ward, M. D.; McCleverty, J. A.; Jeffery, J. C. Coord. Chem. ReV. 2001, 222, 251-272. (11) Ruben, M.; Rojo, J.; Romero-Salguero, F. J.; Uppadine, L. H.; Lehn, J. M. Angew. Chem., Int. Ed. 2004, 43, 3644-3662. (12) Schmittel, M.; Kalsani, V. Top. Curr. Chem. 2005, 245, 1-53. (13) Lee, H.; Kepley, L. J.; Hong, H. G.; Mallouk, T. E. J. Am. Chem. Soc. 1988, 110, 618-620. (14) Evans, S. D.; Ulman, A.; Goppertberarducci, K. E.; Gerenser, L. J. J. Am. Chem. Soc. 1991, 113, 5866-5868. (15) Watanabe, S.; Regen, S. L. J. Am. Chem. Soc. 1994, 116, 8855-8856. (16) Ansell, M. A.; Cogan, E. B.; Neff, G. A.; von Roeschlaub, R.; Page, C. J. Supramol. Sci. 1997, 4, 21-26. (17) Thomsen, D. L.; Phely-Bobin, T.; Papadimitrakopoulos, F. J. Am. Chem. Soc. 1998, 120, 6177-6178. (18) Byrd, H.; Holloway, C. E.; Pogue, J.; Kircus, S.; Advincula, R. C.; Knoll, W. Langmuir 2000, 16, 10322-10328. (19) van Manen, H. J.; Auletta, T.; Dordi, B.; Schonherr, H.; Vancso, G. J.; van Veggel, F.; Reinhoudt, D. N. AdV. Funct. Mater. 2002, 12, 811-818. (20) Abe, M.; Michi, T.; Sato, A.; Kondo, T.; Zhou, W.; Ye, S.; Uosaki, K.; Sasaki, Y. Angew. Chem., Int. Ed. 2003, 42, 2912-2915. (21) Krass, H.; Papastavrou, G.; Kurth, D. G. Chem. Mater. 2003, 15, 196203. (22) Menozzi, E.; Pinalli, R.; Speets, E. A.; Ravoo, B. J.; Dalcanale, E.; Reinhoudt, D. N. Chem.sEur. J. 2004, 10, 2199-2206. (23) Kepley, L. J.; Sackett, D. D.; Bell, C. M.; Mallouk, T. E. Thin Solid Films 1992, 208, 132-136. (24) Moav, T.; Hatzor, A.; Cohen, H.; Libman, J.; Rubinstein, I.; Shanzer, A. Chem.sEur. J. 1998, 4, 502-507. (25) Hatzor, A.; Moav, T.; Cohen, H.; Matlis, S.; Libman, J.; Vaskevich, A.; Shanzer, A.; Rubinstein, I. J. Am. Chem. Soc. 1998, 120, 13469-13477. (26) Hatzor, A.; van der Boom-Moav, T.; Yochelis, S.; Vaskevich, A.; Shanzer, A.; Rubinstein, I. Langmuir 2000, 16, 4420-4423. (27) Doron-Mor, H.; Hatzor, A.; Vaskevich, A.; van der Boom-Moav, T.; Shanzer, A.; Rubinstein, I.; Cohen, H. Nature 2000, 406, 382-385.
10.1021/la0527745 CCC: $33.50 © 2006 American Chemical Society Published on Web 01/24/2006
Assembly of Coordination Nanostructures on Oxides
amate ligand (Scheme 1),28 as well as to branched multilayers, by using the C3-symmetrical hexahydroxamate ligand HH (Scheme 1).29 The objective of the present work is to apply coordination self-assembly schemes, previously developed by us for Au surfaces, to oxide surfaces, accomplished by covalent functionalization of the oxide surface with a ligand monolayer. To this end, SAMs of (3-glycidylpropoxy)trimethoxysilane (GPTMS, Scheme 1) were prepared and characterized on oxide surfaces, and their reactivity toward two ligand-bearing amines was investigated: (i) The epoxy-terminated SAM was converted to a pyridine-terminated surface by reaction with 4-aminomethylpyridine (4-AMP, Scheme 1). (ii) The epoxy group was reacted with deferoxamine (DFX, Scheme 1), providing a hydroxamatefunctionalized surface. The ligand-functionalized surfaces served as anchors for self-assembly of coordinated monolayers and multilayers, that is, (i) binding of cobalt tetraphenylporphyrin (CoTPP) to the pyridine-terminated SAM30-36 and (ii) binding of Zr4+-coordinated layers of the branched hydroxamate ligand HH (Scheme 1) as well as ligand-functionalized Au NPs (Scheme 1) to the hydroxamate-terminated SAM.24,25,27-29,37 The systems were characterized by ellipsometry, water contact angles, atomic force microscopy (AFM), Fourier transform infrared (FTIR) spectroscopy, and transmission UV-vis spectroscopy and compared to analogous structures prepared on Au surfaces. Experimental Section Chemicals and Materials. Methanol (AR, Mallinckrodt), ethanol (AR, Baker), H2SO4 (95-98%, Palacid, Israel; and 98% extra pure, Merck), NH3 (25%, Frutarom, Israel), H2O2 (30%, Frutarom), dimethyl sulfoxide (DMSO; AR, Merck), deferoxamine mesylate salt (DFX; 95%, Aldrich), zirconium(IV) acetylacetonate [Zr(acac)4; 99%, Strem), 4-aminomethylpyridine (4-AMP; 98%, Aldrich), and 5,10,15,20-tetraphenyl-21H,23H-porphine cobalt(II) (CoTPP; Aldrich), were used as received. 3-(Glycidyloxy)propyltrimethoxysilane (GPTMS) (>97%, Aldrich) was distilled under vacuum and stored under N2 at 4 °C prior to use. Toluene (AR, Frutarom, Israel) was distilled over CaH2 (following reflux for several hours) under dry atmosphere and stored over activated molecular sieves (activation at 350 °C, 4 h) under N2. Water was triply distilled. Samples were dried with dry household N2 (>99%). Atomic Force Microscopy. Dynamic-mode AFM measurements were carried out in air, by use of a PicoSPM instrument (Molecular Imaging). The tips used in all measurements (dynamic and contact modes) were CSC12 (MikroMasch, Estonia). Transmission UV-Vis Spectroscopy. Transmission spectra were obtained with a Varian Cary 50 UV-vis spectrophotometer. All measurements were carried out in air, by use of a homemade holder designed for reproducibility of the sampled spot. Spectra were recorded with a bare glass substrate as baseline. (28) Wanunu, M.; Popovitz-Biro, R.; Cohen, H.; Vaskevich, A.; Rubinstein, I. J. Am. Chem. Soc. 2005, 127, 9207-9215. (29) Wanunu, M.; Vaskevich, A.; Cohen, S. R.; Cohen, H.; Arad-Yellin, R.; Shanzer, A.; Rubinstein, I. J. Am. Chem. Soc. 2005, 127, 17877-17887. (30) Offord, D. A.; Sachs, S. B.; Ennis, M. S.; Eberspacher, T. A.; Griffin, J. H.; Chidsey, C. E. D.; Collman, J. P. J. Am. Chem. Soc. 1998, 120, 4478-4487. (31) Kalyuzhny, G.; Vaskevich, A.; Matlis, S.; Rubinstein, I. ReV. Anal. Chem. 1999, 18, 237-242. (32) Ashkenasy, G.; Kalyuzhny, G.; Libman, J.; Rubinstein, I.; Shanzer, A. Angew. Chem., Int. Ed. 1999, 38, 1257-1261. (33) Da Cruz, F.; Driaf, K.; Berthier, C.; Lameille, J. M.; Armand, F. Thin Solid Films 1999, 349, 155-161. (34) Kalyuzhny, G.; Vaskevich, A.; Ashkenasy, G.; Shanzer, A.; Rubinstein, I. J. Phys. Chem. B 2000, 104, 8238-8244. (35) Kalyuzhny, G.; Vaskevich, A.; Schneeweiss, M. A.; Rubinstein, I. Chem.s Eur. J. 2002, 8, 3850-3857. (36) Arima, V.; Fabiano, E.; Blyth, R. I. R.; Delia Sala, F.; Matino, F.; Thompson, J.; Cingolani, R.; Rinaldi, R. J. Am. Chem. Soc. 2004, 126, 1695116958. (37) Doron-Mor, I.; Cohen, H.; Cohen, S. R.; Popovitz-Biro, R.; Shanzer, A.; Vaskevich, A.; Rubinstein, I. Langmuir 2004, 20, 10727-10733.
Langmuir, Vol. 22, No. 5, 2006 2131 Ellipsometry. Ellipsometric measurements were carried out with a Rudolph Research Auto-EL IV null ellipsometer, at an angle of incidence φ ) 70° and a wavelength λ ) 632.8 nm. The same four points on the Si substrates were measured on each sample before and after self-assembly. A 2-nm-thick native SiO2 layer, as determined by ellipsometry, was taken into account in the calculations. Contact-Angle Measurements. Advancing and receding water contact angles (CAs) were measured by use of a computerized CAM100 instrument and software (KSV Instruments, Finland). Three drops (ca. 5 µL) were analyzed for each sample. CAs were measured in three different spots on each sample. Reflection-Absorption FTIR Spectroscopy. FTIR spectra were recorded with a N2-purged Bruker Equinox 55 spectrometer operating in the reflection mode (80° incidence angle), equipped with a liquid N2-cooled mercury-cadmium-telluride (MCT) detector. Data were collected at a resolution of 2 cm-1, and 1024 consecutive scans were taken for both background and sample. The background was a clean, bare Si/SiO2 substrate. Monolayers of GPTMS. Si wafers (boron-doped, polished, 〈111〉 orientation, F ) 20-30 Ω‚cm, International Wafer Service), glass (0.3 mm thick, microscope cover slips no. 3, Marienfield, Germany) and quartz slides were cut into 1.0 × 2.0 cm pieces, cleaned with piranha solution (1:3 H2O2 30%/H2SO4 95-98%) for 30 min, followed by NH3:H2O2:H2O (1:1:2) solution at 70 °C for 30 min. (Caution: Piranha solution reacts Violently with organic materials and should be handled with extreme care.) The slides were then thoroughly rinsed with water and stored in water before use. A cleaned, wet substrate was dried thoroughly under a N2 stream and placed in a 1% (v/v) solution of GPTMS in dry toluene for 5 min. Following adsorption, the substrate was thoroughly rinsed with toluene, sonicated in toluene for 5 min, and dried under N2. Only fresh GPTMS deposition solutions were used (
