Azo-silane SAMs

In this section, we discuss the photo-orientation of azobenzenes in molecularly thin SAMs by means of UV-vis spectroscopy and surface plasmons (SPs). The structural formula of 4-(6-carboxy-(3-amidopropyl)triethoxysilane)-4 -pentylazobenzene, referred to as azo-silane, which leads to a self-assembled monolayer, is shown in Figure 4.1 (top). Azo-silane SAMs (see schematic in Figure 4.1, bottom) for the UV-vis spectroscopy and surface plasmons experiments were prepared as reported elswhere. ... 

UV (360 nm) and blue (450 nm) light irradiations of the ultrathin azo-silane SAMs clearly induce the forth, i.e., trans—>cis, and back, i.e., cis—>trans, photoisomerization of azobenzene molecules (see Figure 4.2A). The real-time dependence of the absorbance of the sample during the thermal cis—>trans back reaction is not a monoexponential decay (see Figure 4.2B). This decay shows a complex multiexponential relaxation behavior that could be fit neither by a monoexponential decay nor by a biexponential relaxation. Nevertheless, a monoexponential decay could be fit to the data acquired over... 

Figure 4.3 shows the photo-orientation, i.e., the dichroism, observed in the azo-silane SAMs. These spectra were obtained after 3 minutes of irradiation with linearly polarized UV light. It is clear that the absorption, Absx, recorded with the probe light linearly polarized perpendicular to the initial UV-light polarization, is higher than the absorption, Abs//, recorded with the probe light linearly polarized parallel to the initial UV-light polarization. Identical spectra were recorded for both Abs// and Absx prior to UV irradiation (only... 

This chapter is organized as follows. Section 4.2 addresses the study of photoisomerization and photoinduced orientation of azobenzene molecules at the molecular level in SAMs of azo-silane molecules. Section 4.3 discusses photoinduced effects in supramolecular assemblies, i.e., LBK multilayer structures containing azobenzene molecules, and compares the photoinduced movement of azobenzenes in these structures to that observed in spin-cast films. Section 4.4 focuses on the isomerization and sub-Tg photoinduced orientation in a series of very high Tg (up to 350°C) nonlinear optical polyimide and thermoplastic donor-embedded polyurethane polymers containing azo dye, especially focusing on polymer structure-Tg-photoinduced molecular movement relationships. Section 4.5 describes pressure effects on photoisomerization and photo-orientation in films of a PMMA polymer containing azo dye. Finally, we make some concluding remarks in Section 4.6. 

For the azo-silane layers, assuming a value equal to 1.45, at 632.8 nm, for the refractive index, normal to the plane of the layer, our SAM could best be described by a layer thickness of 9 A (i.e., an optical thickness of 13.1 A). This is considerably thinner than would be expected for a fully extended azosilane molecule (ca. 30 A). This may be better understood by comparing the... 

Figure 8. Top Structural formula of 4-[6-carboxy-(3-amidopropyl)triethoxysilane]-4 -pentylazobenzene, referred to in the text as azo-silane, that leads to a self-assembled monolayer. Bottom idealized schematic drawing of a SAM on a Si02 substrate.

Figure 9. Top PSP resonance of the bare Ag substrate (dosed circles) after coating with a self-assembled monolayer the azo-silane (open circles) the inset shows the thickness of Ag, SiO,, and the SAM. Bottom Optical thickness change as obtained by recording the reflected intensity of the same sample at a fixed angle of incidence (6 = 45°, cf. top) while irradiating the moments of turning the irradiation light on and off are indicated by arrows.

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