AVS2001 Session OF+SS-ThP: Molecular Aspects of Organic Films Poster Session

Thursday, November 1, 2001 5:30 PM in Room 134/135
Thursday Afternoon

Time Period ThP Sessions | Topic OF Sessions | Time Periods | Topics | AVS2001 Schedule

OF+SS-ThP-1 In-situ Characterization of Photoisomerization Process and Thermal Stability of Highly Photoreactive SAMs on Gold with PM-IRRAS
T. Wei (National Institute of Advanced Industrial Science and Technology (AIST), Japan); K. Tamada (AIST and Frontier Research System, RIKEN, Japan); H. Akiyama, K. Yase (AIST, Japan); S. Kim (Hanyang University, Korea)
In this paper, we discuss conformational change of photoreactive azobenzene SAMs composed of unsymmetrical disulfides on Au(111)/mica under UV/Vis photoirradiation, by use of polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS). Two different azobenzene dyes are utilized in this study; One is a conventional azobenzene unit, and another is a "CH3-attached azobenzene" unit, in which methyl group is introduced to the azobenzene ring to avoid dye aggregation sterically. The "CH3-attached azobenzene" SAM exhibited the stronger nas-CH2 peak at higher frequency position compared with the conventional azobenzene SAM, sugesting more disordered film structures due to the methyl group. For in situ observation of photoisomerization reaction, we performed PM-IRRAS measurements under irradiation of 365nm UV light for cis, and 440nm Vis light for trans. For both unsymmetrical disulfide SAMs, with conventional azobenzene unit (C6AzSSC12) and with "CH3-attached azobenzene" unit (C6Az(Me)SSC12), the intensities of n(benzene ring) and nas (c-o-ph) vibration modes clearly decreased after UV irradiation, as a evidence of photo-isomerization reaction taking place. These IR spectrum changes by photoirradiation were not detected for azobenzene thiol SAMs. After annealing in oven at 100°C for three hours, the IR spectra of both disulfides (C6AzSSC12, C6Az(Me)SSC12) changed to the direction of more disordered or tilted chains, however, the change of C6Az(Me)SSC12 is rather larger than that of C6AzSSC12. These results were compared with our SPR and AFM data for thermal stability.
OF+SS-ThP-3 Scanning Tunneling Microscopy Investigation of the Self-Assembly of Photochromic Molecules on Au(111)
T. Fritz, S. Mannsfeld, T.W. Canzler (TU Dresden, Institut fuer Angewandte Photophysik, Germany); S. Stumpf, K. Gloe (TU Dresden, Institut fuer Anorganische Chemie, Germany); K. Leo (TU Dresden, Institut fuer Angewandte Photophysik, Germany)
The self-organization of photochromic molecules on Au(111) surfaces has been investigated by Scanning Tunneling Microscopy (STM). Self-assembly films of the organic molecule 6-[4-(phenylazo)phenoxy]hexane-1-thiol (AzoC6) have been prepared by immersion of epitaxial gold films on mica in ethanolic solutions (1mmol) for 24 h up to 72 h. High-resolution STM images, using a NanoScope III in air, reveal the ordered growth of AzoC6 in several domains, typically 20 nm in size. A detailed structural analysis was performed on drift-corrected images. In contrast to literature results where a so-called bundle model was suggested which can hardly explain the growth of rather extended domains, we will show evidence that a molecular lattice is formed which is commensurate with the Au(111) surface lattice. The two-dimensional unit cell contains two AzoC6 molecules. All experimental findings are compared to theoretical calculations, based on a geometric lattice match algorithm.
OF+SS-ThP-4 On the Relation between Experimental Vibrational Spectra and Spectra Determined from Ab Initio Calculations: Small Organic Molecules on Single Crystal Metal Surfaces
P. Uvdal, M.P. Andersson (Lund University, Sweden); A.D. MacKerell, Jr. (University of Maryland)
Using small organic molecules, alkoxies and pyridine, adsorbed on single crystal metal surfaces we show that a detailed understanding of the vibrational spectra is possible with the aide of ab initio electronic structure calculations. Specifically we investigate on an ab initio level the surface induced alteration of (a) isotopic shifts (b) intramolecular coupling and (c) Fermi resonance coupling between binary modes and fundamentals. The experimental data is obtained in UHV using a FTIR spectrometer.
OF+SS-ThP-5 Surface Plasmon Resonance Techniques for In Situ Detection of LCST Behavior on Surface-Grafted Polymer Films
S. Mendez, S. Balamurugan, L.K. Ista, G.P. Lopez (University of New Mexico)
Thin films of the temperature responsive polymer, poly(N-isopropylacrylamide) (PNIPAAM), were polymerized in situ on azo-initiator derivatized self-assembled monolayers (SAMs). Carboxylic acid and methyl-terminated alkanethiols were used to form mixed component SAMs on gold substrates. Reaction of the COOH moieties with Woodwards reagent K and an amine containing azo-initiator resulted in immobilization of the initiator on the surface. PNIPAAM was then grown from the surface upon exposure of the surfaces to heat and monomer solution. Varying the concentration of COOH-thiolate within the original SAM allowed us to control the surface coverage of the polymer. Surface plasmon resonance (SPR) was used to detect the lower critical solubility temperature (LCST) transition of these surface-grafted polymers by taking advantage of a difference in both thickness and refractive index of the polymers in their relaxed (low temperature) and collapsed (high temperature) states. Realtime, in situ reflectance measurements of the PNIPAAM films immersed in water were taken as the temperature of the samples was raised. The effect of surface coverage on the position and degree of the transition was also examined.
Time Period ThP Sessions | Topic OF Sessions | Time Periods | Topics | AVS2001 Schedule