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Home > Scientific teams > Electrochemistry and Thin Films > Molecular Organization and Interactions at surface

Photoswitchable surfaces

by Rosso Michel - published on , updated on

Participants : P. Allongue, J. –N. Chazalviel, C. Henry de Villeneuve, F. Ozanam

PhD students : T.L. Nguyen Le (2014), S. Klaes (2017)

Collaboration : K. Rück-Braun - Institut für Chemie – TU Berlin - Germany

The design of “smart” surfaces responsive to external stimuli (light, electromagnetic field, chemical environment…) is attracting considerable interest because of their great potential for a wide field of applications (optoelectronics, bio/chem sensors, microfluidic, life science…). Within this context the anchoring of switchable organic molecules on solid surfaces opens interesting perspectives to construct active surfaces with properties tailored at molecular scale.

We are interested in the photoswitching properties of organic photochromes belonging to the family of Indolyl Fulgimide (Fig. 1a). The fulgimide groups are covalently anchored through amide linkage on “NHS activated“ acid monolayers grafted on oxide free silicon surfaces.

The open (E) and closed (C) isomers exhibit different IR absorption bands which makes possible a non destructive read-out of the photoisomerization by FTIR spectroscopy (Fig.1b). Pure monolayers with solely - open (E) or closed (C) forms – are prepared and the photocommutation is investigated by in situ monitoring the shift of the main carbonyl peak (νC=0, at 1690-1700 cm-1) under UV or Vis illumination.

The figure 1c shows that the photocommutation is reversible in between two photostationnary states PSSvis and PSSUV. A quantitative analyis of the intensity of IR bands corresponding to the NHS and/or COOH anchoring sites disappeared after the fulgimide coupling allowed to determine the initial concentration of fulgimides on the surfaces and the isomeric composition at the PSSs (Fig. 1d). Our results show that in the case of dense monolayers (1.7 1014 fulgimides/cm2) a large part of the fulgimides undergoes isomerization with only about 20% of them that are non photoactive because of steric hindrance. A full commutation is observed when the fulgimide density is below the maximum compactness.

Figure 1 : (a) Structures and UV-Vis isomerisation of Indolyl fulgimide compounds. (b) IR specta of pure monolayers with solely C-isomers (blue plot) or E-isomers (red plot). (c ) Variation of the composition of a pure C monolayer over successive Vis/UV illumination sequences. The black and red dots give respectively the concentration of closed-forms (C) and open-forms (E+Z). (d) Isomeric compostion at the two photostationnary states PSSvis (odd cycles) and PSSUV (even cycles).

Publication :

 C. Henry de Villeneuve, F. Michalik, J.-N. Chazalviel, K. Rück-Braun, and P. Allongue, "Quantitative IR Readout of Fulgimide Monolayer Switching on Si(111) Surfaces," Advanced Materials 25 (3), 416-421 (2013)