CHROMADYNE

Research in photochromic molecules is considered as one of the possible routes to the post-silicium era in opto-electronics, a major challenge at the 2020 horizon. Photochromic molecules have the specificity to be stable under two isomeric structures, the absorption spectra of which do not overlap in a wide range. Moreover, these molecules can switch from one isomer to the other by interaction with a photon at the maximum of absorption, or thermally. This intrinsic property of photochromic molecules has its origin in the electronic structure of the two isomeric forms: the electron delocalization is very different in both isomers. Indeed, one isomer has usually a delocalized electronic cloud and absorbs the visible light, whereas no such complete delocalization exists in the other one. There, the electron clouds are shared between two areas that are poorly connected, thus pushing the absorption to the UV. Thus, this property makes the photochromic molecules really good candidate for the use as optical memories or electro-optic switches. For this use, photochromic molecules must be coupled to macroscopic systems through a series of adaptators, those objects of smaller scale being other molecules or nano-objects linked to the photochromic molecule. The goal of this project is to provide a conceptual and semi-quantitative information on the coupling between selected photochromic molecules and several types of environment (gas phase, deposited on rare gas cluster, solvated with a given number of molecules, interaction with a nanoparticule) for a direct use by electro-optics devices designers. This project deals with the full characterization of the electronic structure dynamics and reactivity of some photochromic molecules in various environment previously mentioned. A concerted approach will involve spectroscopic and dynamics experiments complemented by molecular dynamics calculations and TD-DFT calculations. We will focus on 3 main mechanisms, which are involved in Spiropyrans, Diarylethane and Anyls. These three classes of molecules were chosen for the following reasons: i) Spiropyrans show a mechanism involving a zwitterionic state, as observed in gas phase by our group. This molecule is also sensitive to the molecular environment. ii) Diarylethene is the most promising molecule for electro-optical purposes, because of its high efficiency coupled to its rigidity. Here the molecular motion is small in the isomerisation process which can be accomplished as well in a crystal, as in a single molecule. Furthermore, the large electronic clouds make the molecule sensitive to the proximity of a metallic particle. iii) Anyls have a fundamental interest, as their property are induced by the shift of an H atom, like in Acetylacetone and fully examined in our laboratory. Protic solvents can also perturb strongly their dynamics. Moreover Anlys are used are non linear optical devices. This project will benefit from the GDRI PHENICS network for the development of collaboration between France, Japan, China and Russia in the field of photochromic molecules. This project will link 4 young scientists (<36 year old) very closely connected geographically and scientifically, each of them leading a specific and different task, directed at a better understanding of the interaction between light - with the photochromic molecules - molecular environment. This project intends to initiate the formation of a new team dedicated to the elaboration of fundamental concepts in molecular chemical-physics which are directly linked to a valorization process through collaborations already established. The creation of this new team is fully supported by the head of the Laboratoire Francis Perrin.