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Synthesis of photoactive compounds for surface modification (e.g. SiO2)

Depending on the desired application, the surface characteristics can be tailored. In the frame of a BMBF funded project (OSOKA, FKZ 16SV3537) azobenzene compounds were synthesized for photo-controllable surface modification. The cis/trans isomerization of the diazo group allows changing the surface characteristics by irradiation at a certain wavelength. Different azobenzene based organosilanes were investigated with different functionalities.
Currently, a photo-induced reversible contact angle change with diiode methane of 5° was observed by non-substituted thiol compound. For photoswitchable compounds with different functionalities and silane anchor, contact angle changes with water in oil of 6°-8° can be achieved. The activation energy for photoisomerization was calculated by the Arrhenius equation.

<b><sup>1</sup>H-NMR of a synthesized azobenzene compound as terminal alkene for introducing an anchor group. <sup>1</sup>H-NMR (CDCl<sub>3</sub>, 300MHz) δ[ppm] 0,92 (t, 3H, CH<sub>2</sub>C<I>H</I><sub>3</sub>); 1,33 (m, 16H, C<I>H</I><sub>2</sub>); 1,6 (m, 2H, CH<sub>2</sub>C<I>H</I><sub>2</sub>CH<sub>2</sub>Ar 1,83 (m, 2H, CH<sub>2</sub>= CHC<I>H</I><sub>2</sub>CH<sub>2</sub>); 4,0 (t, 4H, CH<sub>2</sub>C<I>H</I><sub>2</sub>OAr); 5,01 (m, 2H, C<I>H</I><sub>2</sub>=CHCH<sub>2</sub>); 5,7 (m, 1H, CH<sub>2</sub>=C<I>H</I>CH<sub>2</sub>); 7,00 (d, 4H, Ar-H); 7,85 (d, 4H, Ar-H)</b>

Left. Series of UV/vis spectra of azobenzene with silane anchor with simultaneous irradiation at lambda = 350 nm. The diazo group switches from the trans (black spectrum) in the cis state.
Right. Reversible molecular switch at different wavelength¸ irradiation at lambda = 350 nm and 445 nm.

[1] S. Möller, U. Pliquett, C. Hoffmann, Synthesis of molecular photoswitches based on azobenzene with organosilane anchor, RSC Advances 2 (11/2012) 4792–4801.
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