Innovative Photoswitch based on Excited State Cation Transfer – ExStaCaT

The ExStaCat project is based on the complementarity of the approaches developed by the three research units of the consortium, namely :
- Predictive in silico evaluation of the structural and optical properties of series of molecules potentially interesting for the realization of ESCT photoswitches by quantum chemistry.
-Synthesis of the best candidates within two families pof compounds
-Characterization of the properties of photo-switches by stationary and transient spectroscopic methods.

The first studies focused on the in silico prediction of the structural and optical properties of a series of molecules derived from the Betaine pyridine (PyB) molecule in order to characterize the excited states exhibiting charge transfer character, to quantify this character and to calculate the relative complexation constants between each molecule and the Ca2+ cation. Theoretical studies have also focused on the prediction of cation photoejection after photoexcitation of organometallic complexes. The synthesis of the best candidates has been launched and some molecules are already available. Time-resolved spectroscopic studies have been conducted on a first iridium complex as well as on some molecular fragments carrying complexing groups. A spectral signature of the cation photoejection seems to have been highlighted and still needs to be confirmed by further studies.

The work to come is a direct continuation of the work carried out in the first phase of this project, namely : i) prediction of the optical properties, complexing constants and cation transfer processes in the excited state for Betaine pyridine-based molecular photocommutators and iridium complexes (WP1 and WP2), ii) synthesis of the most promising molecules for these two families (WP1 and WP2), iii) characterization of the translocation of the cation between two sites of the molecule by stationary and time-resolved spectroscopic methods (WP1 and WP2), iv) on the basis of the work carried out on the molecules studied in WP1 and WP2, theoretical study, synthesis and characterization of bistable photocommutators operating by cation transfer in the excited state. This last step is the ultimate goal of the ExStaCat project.

Oral communication :
Laure de THIEULLOY, Clément BAROIS, Cédric MONGIN, Isabelle LERAY, Stéphane ALOÏSE, Guy BUNTINX, and Aurélie PERRIER Theoretical study of a new class of photoswitches based on the Excited-State Cation Transfer, Conférence “PhotOnline” organisée par SP2P 15/10/20.

Nowadays, smart molecular photoswitches able to toggle between, at least, two states with different physical responses are still receiving an increasing attention. So far, photoswitch principles are always based on the same elementary photochemical processes such as Intramolecular Charge Transfer (ICT) or Excited State Proton Transfer (ESPT). In this project, we propose to design a new class of photoswitches based on Excited State Cation Transfer (ESCT). However, even though numerous cation photoejection-based systems have been developed during the last three decades, molecular photoswitches based on ion translocation between two binding sites remains largely unexplored. The ExStaCaT project proposes to design and to study well-structured molecular architecture, to provide an efficient ESCT photoswitch, composed of different photo-active and complexing units linked to a cation photoejector in order to control the position and the movement of the cation within the system, thus triggering specific and trackable spectroscopic responses. The first step will be to develop a proof of concept ESCT system, followed, in second step, by the conception of smart ESCT photoswitches (bistable).
To explore this new field of photo-organic switching chemistry, this project relies on the development of innovative molecular design strategies supported by a consortium that combines organic synthesis (PPSM), molecular design and (TD-)DFT calculations (IRCP) and time-resolved spectroscopy to rationalize and then control the basic photoinduced processes (LASIR). Several systems will be designed with a strategy based on well-known and convergent organic chemistry and coupling reactions supported by in-silico molecular design. Moreover, in order to track the ESCT reactions, the development of a two-color dual-pump laser flash spectroscopy will be required. The ExStaCaT project thus aims to explore a new field of organic photochemistry and pave the way towards advanced systems with potential applications as memory storage or logic gate.