Is it possible to ”simply” predict the photoejection of a cation? Example of azacrown-substituted [(bpy)Re(CO) 3 L] + complexes

In the context of designing efficient photocontrolled ion-release systems, we propose a ”simple” computational strategy able to predict the cation photoejection. Our strategy is based on TD-DFT calculations and the analysis of the charge transfer (CT) parameters of the excited states that can be populated for a given excitation wavelength, in the Franck–Condon region. With the help of CT descriptors (the variation of the electronic density, the so-called DCT index and the variation of natural population analysis NPA charges), we aim to identify the CT states presenting a depletion of electronic density on the complexation site after excitation. If the loss of electronic density is large enough in the cation binding site, the population of such a state should be the first step of the mechanism leading to the cation photorelease. We test this strategy on ReAZBAP-Mn+ (Mn+ = Li+, Na+, Mg+, Ca2＋, Ba2+) and ReAZAT-Ba systems, a series of complexes synthesized and studied by Moore and co-workers [Lewis et al. (2004)]. We show that our first-order approach that does not take into account the complex excited-state decay routes, is able to correctly predict the photorelease properties with a success rate of ca. 80 percent. This method should thus be considered as a valuable tool in the framework of the in silico design of light-controlled ion release.