Photo- and Electroinduced Bimodulation of Smart Surfaces – PHOEBUS

Photochromism is simply described as a reversible photinduced change under light irradiation between two states of one molecule, these two states possessing different absorption spectra.Behind these color changes, various physicochemical properties could be reversibly changed or modulated. Formation of self-assembled monolayers is a powerful method to prepare spatially controlled surfaces and it is expected to be the easiest way transfer the solution properties to more condensed matter so devices could be obtained.

Synthetic efforts have allowed to access to various triphotochromic compounds and two of the used chromophore showing also electrochemical properties and one of these motif being reversibly sensitive to acidity variation. So, the preliminary step toward smart surfaces has been successfully reached.

Synthetic light-activated, electroactive molecular switches on surfaces, so the interaction and communication between sub-components of the multiaddressable targets and surfaces could be seriously considered if the immobilization will not alter the solution properties.

The two first papers have just been submitted for publication.

PHOEBUS addresses the design and elaboration of organized arrays of molecular switches on surfaces. In fact, anchoring molecular-based materials on surfaces is a convenient means to assure their spatial addressability. For this project we aim to design more sophisticated versions integrating two or three switchable functions into a single molecule. The development of this multiswitchable unit will follow two axes, first, the elaboration of an all-photonic system by combination of several photochromic units, second, the development of hybrid system by merging photochromic and electroactive units.

As promising preliminary results were recently obtained by the consortium on diarylethene unit (DAE) covalently linked to indolino[2,1-b]oxazolidine (IOX), this series will be enlarged and an anchoring group will be introduced in order to immobilize them.
However nature, stability of all interconvertible photo- and/or electro-induced forms must be perfectly characterized. In this regards, the photochemical switches will be evaluated by the NMR technique coupled to irradiation. These studies will enable to elucidate the structure of the photoproducts, to determine their thermal dependency and their relative concentrations and to follow quantitatively their evolution during irradiation. Kinetic data will be extracted to ensure a complete understanding of reaction mechanisms. Concerning, the electrochemical component of our multiaddressable derivatives, it will be evaluated first by cyclic voltammetry in order to study the electron transfer and the kinetics of the reaction mechanisms involved and, second, by UV-visible spectroelectrochemistry in order to identify the potential at which a photochromic unit is produced or consumed.

PHOEBUS will focus on SAMs elaboration from our multiaddressable molecular systems. The resulting materials will be fully characterized on their structural characteristics (stability, organization, molecules orientation…) as well as their photo- and electro-switch abilities. Appropriate and powerful techniques (PM-IRRAS, SHG) will be adapted for the investigation of molecular orientation and conformation of the immobilized multiswitches.
The preliminary results hold particular relevance to the design of photoswitchable system for incorporation in the molecular-based electronic systems. It is expected that all isomers show different conductance because the conjugation is changed. Macroscopic alteration of the current which is a truly manifestation of the structural and electronic changes of the molecular monolayer of hybrid DAE-IOX, will be monitored by electrochemistry.
Potential molecular devices arising from our molecular monolayer of hybrid DAE-IOX could operate as 2^3 states logic operator that can be optically and electronically written/erased. Furthermore as IOX motif has been shown to display a large NLO contrast between isomers, it is also planned to use SHG technique as a non-destructive readout. PHOEBUS will assess the feasibility of both approaches.

These ambitious objectives set the stage for a 42-month project that, if funded, will provide unparalleled opportunities to significantly advance the field of surface modulation and to bring to fruition molecular manipulation on the nanoscale. Besides these important applications, the project will also address key fundamental questions relative to multiaddressable molecules and to these surface-bound systems such as the communication between molecular sub-components and between immobilized targets and metallic surfaces that are essential in controlling macroscopic properties. This collaborative program would also be a unique opportunity to aid consolidation of an emerging French group around synthetic light-activated molecular switches on surfaces, gathering together complementary teams with internationally recognized expertise.