Nexus States for Molecular Spintronics : a joint theoretical and experimental study. – NEXUS

Spintronic devices, up to now unique to the field of semi-conductor technology, are intended to manipulate the spin of the electron rather than its charge. The basic working principle of 'classical' spintronics resides in the injection of polarized spin carriers into the conduction band of properly designed microchips to build up transient spin coherences useful for information storage. Our project is aimed at transposing these concepts at the molecular level. Novel Photo-Magnetic Molecular Devices (PMMDs) hereby proposed are intended to perform intramolecular alignment of their inner spins upon light-excitation, which are likened to aforementioned spin coherences but taking place at the molecular level. To generate these intramolecular correlations of spins, we will make use of light-triggered electrons (ET) and energy (EnT) transfers within compact multicomponent inorganic systems. Beyond the aim of the present project, the novelty stems from the fact that we are planning to rely on strong intercomponent electronic and magnetic couplings as novel full functional ingredients. First, we will establish general functional schemes concerning photoactive integrated architectures by bringing out the salient functional combinations essentially based on photosensitizers (P), dendritic connectors (DC, made up of a core, C, and n branches, B) and peripheral units (Pu) of various types (and in particular spin carriers, Sc). We will investigate thoroughly the way(s) these peripheral units may interact via DC. The novel DC function we are presently introducing is actually hosting nexus states of determining importance as they are the effective means by which the n Pus, borne by the DC, are correlated. Yet, we have identified two different types of nexus states (i, ii) attached to specifically designed DCs. On the one hand, (i) there are centred states essentially located on the single core of DC thus ensuring a topologically radial C-(Sc)n magnetic coupling mediated by the n branches of DC. On the other hand (ii), there are delocalised states essentially located at the immediate vicinity of C according to a so-called toroïdal topology, thus correlating the n branches and, consequently, the n dangling Scs. Otherwise, activation of DC will proceed from photo-excitation of remote P unit, which will initiate ET or EnT forward to DC (behaving as an electron- and/or energy-accepting assembly). Intrinsic complexity of the novel DC function relying on intricate magnetic/electronic couplings, possibly dependent on the intramolecular topology, and moreover working in the excited state, is assuredly requiring a fine theoretical analysis prior to embarking on the demanding synthesis of PMMD prototypes. This plural and novel function surely deserves particular attention owing to the prominent role it should play in other numerous advanced photoactive molecular devices. Already emerging in the literature (Gust, Moore) devoted to functional models for artificial photosynthesis, DC function has been successfully used to achieve efficient antenna effects (the Pus are therefore chromophores and luminophores). In order to gain valuable insights into the basic working principle of new PMMDs, we will combine the means of Theory and Experiment. Within this framework, Density Functional Theory (DFT) will be our theoretical method of investigation, providing a satisfactory description of such complex systems and phenomena with a reasonable computational effort. Our final aim is to rationalise the behaviour of PMMDs with the ultimate goal of predicting the emerging properties/functions of new –other– multifunctional photoactive molecular devices. Beyond basic issues, this work should help in designing molecular devices of potential technological interest that can be candidates for application within the domains of (i) information handling and storage, (ii) opto-electronics (including non-linear optics) and (iii) light-energy conversion and storage (including photovoltaïcs) among others... Finally, it is worth mentioning that the strength of our working team is stemming from the complementarity and synergy –that already exist– between the theoretical and experimental partners. Such an integrated assembly is allowing the conception of novel photochemical molecular devices (including PMMDs) from the understanding of their very basic working mode to their actual synthesis and evidencing of their anticipated properties/behaviour.