P. Vanoppen

Expression of chirality by achiral coadsorbed molecules in chiral monolayers observed by STM

The supramolecular packing mode of physisorbed monolayers built up by chiral isophthalic acid derivatives and coadsorbed achiral solvent molecules was imaged at the liquid/graphite interface with scanning tunneling microscopy (STM). The picture on the right shows the submolecularly resolved STM image of an enantiomorphous domain composed of the R enantiomer of the isophthalic acid derivative studied and 1-heptanol molecules; the latter express the chirality of the monolayer. Upon adsorption a racemic mixture is separated into enantiomorphous domains.

Molecular organization of azobenzene derivatives at the liquid/graphite interface observed with scanning tunneling microscopy

Physisorbed monolayers of azobenzene derivatives were studied with a scanning tunneling microscope at the liquid/graphite interface. Three different compounds, namely, 4,4′-di(dodecyloxy) azobenzene (C12(AZO)C12), 5-[ω-(4′-dodecyloxy-4-azobenzene-oxy)dodecyloxy] isophthalic acid (C12(AZO)C12ISA), and 4,4′-bis(ω-[3,5-bis(carboxylato) phenyl-1-oxy] dodecyloxy) azobenzene (ISAC12(AZO)C12ISA) have been investigated. In all cases monolayers could be observed with submolecular resolution at the liquid/graphite interface, allowing one to identify the azobenzene, as well as the other parts of the molecules. For each monolayer structure a molecular model could be composed with a good correspondence to the experimental data. Differences in the observed monolayer structures could be related to the chemical structure of the investigated compounds. The introduction of an isophthalic acid (ISA) headgroup has a profound influence on the monolayer structure because of its capability of hydrogen bond formation with other ...

Mechanical and optical manipulation of porphyrin rings at the submicrometre scale

Scanning probe microscopes (SPMs) and especially the atomic force microscope (AFM) can be used as tools for modifying surface structures on the submicrometre and even nanometre scale. For this purpose an advanced interface has been developed to facilitate these manipulations and greatly increase the number of possible applications. In this paper this interface (the nanoManipulator, developed at the University of North Carolina at Chapel Hill) is implemented on a combined AFM-confocal microscope. This setup allows AFM imaging, manipulations and fluorescence imaging of the same area on the sample. The new setup is tested on ringlike structures of a porphyrin derivative (BP6). A small amount of the fluorescent material could be displaced with the AFM tip. A special tool (sweep mode) allowed a modification of around 130 nm, which was afterwards detectable with the confocal microscope. The resolution attainable in these kind of experiments could go down below 100 nm and is primarily determined by the tip and sample geometry. Comparable with this experiment is the application of a near-field scanning optical microscope (NSOM) to make photochemical modifications. Using the excitation power coming from the NSOM probe the fluorescence can be quenched by bleaching a selected area instead of displacing the material. Application on the BP6 rings led to a modification of 280 nm wide. AFM can perform modifications on a smaller scale but is less selective than NSOM. Optical investigation of the changes after AFM manipulation can give more elaborate information on the modifications. This will extend the possible applications of the techniques and may ultimately go down to the single-molecule level.

Near-field scanning optical microscopy and polymers

Abstract Polymer composite films consisting of fluorescent nanometric particles of dye-labeled latex dispersed in poly(vinyl alcohol) matrices were imaged with an aperture Near-field Scanning Optical Microscope (NSOM). Different films of this type with a thickness of ∼ 25 nm containing latex particles with diameters of 103 nm ± 9 nm or of 14 nm ± 3.7 nm with low particle density were studied. During image acquisition with the NSOM the particles were excited by a tunable argon ion laser. In case of the 103 nm small particles the excitation wavelength, λ, was chosen to be at the maximum or at the red edge of the excitation band at λ = 458 nm or at λ = 488 nm, respectively. In case of the 14 nm small particles the respective films were excited at λ = 488 nm. In both cases strong fluorescence spots with FWHM diameters of λ 2 could be found. Additionally, photobleaching of a single 103 nm small fluorescent latex particle with a NSOM was performed representing a controlled photochemical reaction on a submicrometer length scale. Beside the presentation of the own work, references to the application of near-field optical microscopy to the investigation of thin polymer films are given.

Excited State Probing of Supramolecular Systems on a Submicron Scale

Imaging techniques, such as Confocal Fluorescence Microscopy (CFM) or Near-field Scanning Optical Microscopy (NSOM) [1, 2] are essential techniques to study complex heterogeneous organic thin films by mapping their optical properties. They are complementary techniques having different advantages and disadvantages [3]. CFM is relatively easy to apply and combines a lateral resolution approaching λ/2 with the possibility of layered imaging in the z-direction. In contrast, NSOM has significantly better spatial resolution and offers simultaneous optical and topographic images. Although confocal microscopy has been mostly used for biological applications, the technique has proven to be useful, for example, in the study of colloids [4,5], polymer blends [6] and liquid crystals [7,8].