Photo-Induced Structural Changes in Titanium Alkoxides for Directing Molecular Assembly
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0960-N05-03
Photo-Induced Structural Changes in Titanium Alkoxides for Directing Molecular Assembly J. David Musgraves1, B.G. Potter, Jr. 1, Robin M. Sewell2, and Timothy J. Boyle2 1 Materials Science and Engineering Department, University of Arizona, Tucson, AZ, 85721 2 Advanced Materials Laboratory, Sandia National Laboratories, 1001 University Boulevard, Southeast, Albuquerque, NM, 87106 ABSTRACT The effects of ultraviolet irradiation on a heteroleptic titanium alkoxide ((OPy)2Ti(4MP)2) have been investigated. The molecule has been studied in solution and in thin film form using FTIR and Raman spectroscopies. Quantum computational modeling was used to associate vibrational modes with structural moieties present in the molecule. In all cases examined, a preferential photoinduced modification in vibrational resonances linked to the 4-mercaptophenol (4MP) ligand was observed. In contrast, little or no change was exhibited in the vibrational structure of the OPy ligands. INTRODUCTION Control over materials assembly on the molecular level, and the resultant nanostructure, during the creation of oxide materials from solution has been elusive. One approach to attain this goal is the use of ultraviolet light to directly photocatalyze the formation of intermolecular bonds [1-3]. Other efforts involve the modification of conventional alkoxide precursors with photosensitive chelating agents allowing the photopatterning of areas with completed network connectivity subsequent to conventional sol-gel synthesis [4,5]. The present study is concerned with the preferential modification of local molecular structure, and the ensuing formation of intermolecular bonds, through the photoexcitation of engineered heteroleptic alkoxide molecules. Such an approach would enable the manipulation of reaction kinetics at specific points within the molecular structure and could serve as a tool to bias the formation of bonding topology. The molecule under study is the previously disseminated [6] mononuclear, heteroleptic titanium alkoxide: (OPy)2Ti(4MP)2 [see Figure 1 below where OPy = pyridine carbinol (NC5H4(CH2O)) and 4MP = 4 mercaptophenol (OC6H4(SH))]. Ultraviolet induced changes in vibrational structure have been observed using Fourier Transform Infrared (FTIR) and Raman spectroscopies. Spectra are interpreted in the context of normal mode analyses of energy-minimized molecular structures obtained via density functional theory (DFT) computations.. EXPERIMENTAL DETAILS The (OPy)2Ti(4MP)2 was prepared according to literature procedures [6]. Solution samples for study by FTIR spectroscopy were prepared under glove box conditions in an
atmosphere of dry argon. Powdered (OPy)2Ti(4MP)2 precursor (0.034 g) was dissolved in 5 mL of anhydrous pyridine, to produce a 13 mM solution, and set to stir for 30 min prior to use. A sample of the solution was transferred, while within the glove box, to an FTIR solution cell with a 0.2 mm Teflon spacer. The remainder of the solution was sealed in a scintillation vial to serve as a control specimen and was
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