LAboratoire de Spectrochimie Infrarouge et Raman – UMR 8516
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Description of the subject

Synthesis and photochemical characterization of a novel molecular photoswitch based on Excited State Cation Transfer
Supervisor(s): S. Aloïse

Organic molecular switches can toggle between two (or more) stable states encoding different physical features. They allow complex systems to respond to changes in their environment defined by light, pH, temperature or redox potential etc. Taking benefit of their non-intrusive properties, photoswitches which are actuated by light are fundamental within high interest scientific fields such as molecular electronics, molecular machines, advanced materials and biology.

During his/her Ph-D, the candidate will investigate a new class of elementary photoinduced reaction based on Excited State Cation Transfer (ESCT). This new elementary process involves a cationic intramolecular photo-translocation between two possible complexation sites. An example of such molecule is presented in fig1a. A betaine pyridinium unit (site #1) is a pre-complexation site in the ground state manifold while, in the excited state, complexation occurs into an aza-crown moiety (site #2). The overall cation transfer process is facilitated by the presence of a smart linker being in this case a photochromic azobenzene. The interest of ESCT reactions can be found in biological issues like the manipulation of cation flux inside ionic channels. Thanks to the reversibility of the process, this approach can be complementary to other caged compounds[1] and genetically modified systems.[2]

To explore this new field of photo-organic switching chemistry, the candidate will have access to several ultrafast absorption or emission spectroscopic systems (pump-probe experiments) allowing to cover different reaction times in the femtosecond to millisecond temporal windows. In particular, after deriving the main photochemical pathways, he/she will have to answer the fundamental  (and challenging) question: is the cation traveling between Site#1 and site#2?

[1] Momotake, N. Lindegger, E. Niggli, R. J. Barsotti G. C. Ellis-Davies; Nat Methods, 2006, 3, 35-40

[2] T. Ishii, K. Sato, T. Kakumoto, S. Miura, K. Touhara, S. Takeuchi, T. Nakata; Nature communications, 2015, 6, 8021.PhDproposal_ 2018_ESCT_Eng-Aloise