Up to now, only a small number of coupled molecular photochromic entities have been proposed and they all undergo a series of bottlenecks that need to be solved. So, by providing ways to circumvent these problems, MARCHES should provide a path towards architectures able to keep and deliver inside a single molecule more information than the usual binary units, subsequently helping the rise to a prospective generation of storage.
APPLYING AND EXTENDING TD-DFT THEORY: WHY?
Amongst the available ab initio theories for excited states, Time-Dependent Density Functional Theory (TD-DFT) stands as one of the most valuable approach in terms of balance between accuracy and computational requirements. Nevertheless TD-DFT undergoes a series of specific limitations in this practical implementations, though the theory is of exact mathematically essence. For instance, TD-DFT was originally viewed as inadequate for simulating charge transfer states, where the electron jumps between two well-separated chemical groups upon photon absorption. This problem was solved recently thanks to the developments of range-separated hybrids (RSH, also referred to as long-range corrected hybrids). In RSH, the DFT/exact exchange mixing percentage is explicitly dependent of the inter-electronic distance and one reaches a physically sound description for both local and charge transfer electronic transitions. This example clearly highlights that the interest of methodological improvements is not restricted to a trifling community of quantum chemistry specialists but might be a first step for tackling a wider range of chemical and physical problems.
THE FINAL TARGET: COUPLED PHOTOCHROMES
Only a few numbers of molecules incorporating more than a single photoswitchable unit have been synthesised up to now, and they represented only a limited palette of choice. Our previous model investigations are already at the border of what can be done today (due to the size of the EES space, typical calculations last for weeks), they should be completely recast to answer great challenge tackled by MARCHES: the rational design of architectures that overcome all the actual limitations, i.e that are multi-addressable, that show emergent features (non-additive spectra and polarisabilities).
Thus, the team have to:
- Understand how the relative positions of the units (linear, star, square, hexagonal … shapes) influence the nature and relative energies of the excited-states
- Investigate the possible pathways on the EES potential energy surfaces
- Propose auxochromic groups that keep the photochromic state alive after the first photoreaction
- Identify the key parameters limiting parasite reactions
- Take into account the medium surrounding these switches
- Perform these five tasks for different of coupled photochromes
- The developments and improvements of theoretical models firstly impact on the active scientific community in quantum chemistry and physics
- This project is bound to open innovative research paths and gives rise to new broad-scope concepts, eventually leading to new technologies
- MARCHES could initiate new 3D storage materials, or at least assess possibility to provide effective molecular building blocks.
To maximize the impact of the project, specific transfer-of-knowledge activities are planned, targeting mostly researchers from other fields, so that project results are disseminated, opening new research paths in various domains. (see the section “EVENTS”)