Exploring excited state potential energy profile and luminescence properties of uranyl-based complexes by TRLFS and ab initio methods
Résumé
Uranyl complexes have been the subject of many research works for fundamental chemistry of actinides, environmental issues, or nuclear fuel cycle processes. The formation of various uranyl complexes, with organic and inorganic ligands in solution must be characterized for a better understanding of U(VI) speciation. As uranyl-ligand interactions and the symmetry of the complexes affect the electronic structure of U(VI) and thus its luminescence properties, time-resolved laser induced fluorescence spectroscopy (TRLFS) is one of the major techniques to characterize U(VI) complexes, with high sensitivity and selectivity. However, most of the relevant systems have complex chemical composition in solution and the identification of each species from spectroscopic data is challenging.
In our study, the synergy between TRLFS and ab initio-based interpretation appears as a promising route for complexation data. Luminescence spectra of uranyl complexes in solution show in general a narrow energetical range about 6000 cm-1 and we can identify a single electronic transition between the initial and target states with the vibrationally resolved band [1].
The main challenge consists in exploiting a computationally cheap and effective theoretical approach, in a relativistic context, to characterize the main spectral parameters and first excited state of symmetrical uranyl compounds (i.e. UO2Cl42-, UO2F53-, UO2(CO3)24- etc. ) with different organic or inorganic counter ions after the photo-excitation and compute with high accuracy vibronic progressions observed in experiments. The most important steps are the ground and excited state geometry optimizations followed by normal modes calculations and calculations of the Franck-Condon vibronic integrals.
The time-dependent density functional theory (TD-DFT) with hybrid functionals is one of the most popular methods for electronic structure modelling of larger actinide complexes, as it is computationally less expensive than wave-function based methods. TD-DFT together with the CAM-B3LYP functional is able to reconcile the flaws in the determination of vertical excitation and emission energies, that was a challenging task for DFT several years ago.
As a benchmark system serving the purpose of assessing the accuracy of our theoretical protocol, the uranyl tetrachloride UO2Cl42- was selected because of the extensive amount of structural and spectroscopic data available [2]. A good agreement was found between ours and previously obtained theoretical data (structural parameters, orbitals nature, excitation energies) [3]; the final luminescence spectrum is in remarkable agreement with our TRLFS measurements. In the framework of this conference I will guide you through the various steps of the theoretical methodology, and illustrate how useful it is to assign recorded TRLFS spectra.
References
[1] J. Visnak and L. Sobec, EPJ Web of Conferences 128, 02002 (2016).
[2] R.G. Denning et al., Chem. Phys. Letters, 180, 101 (1991).
[3] K. Pierloot et al., J. Chem. Phys., 123, 204309 (2005).
In our study, the synergy between TRLFS and ab initio-based interpretation appears as a promising route for complexation data. Luminescence spectra of uranyl complexes in solution show in general a narrow energetical range about 6000 cm-1 and we can identify a single electronic transition between the initial and target states with the vibrationally resolved band [1].
The main challenge consists in exploiting a computationally cheap and effective theoretical approach, in a relativistic context, to characterize the main spectral parameters and first excited state of symmetrical uranyl compounds (i.e. UO2Cl42-, UO2F53-, UO2(CO3)24- etc. ) with different organic or inorganic counter ions after the photo-excitation and compute with high accuracy vibronic progressions observed in experiments. The most important steps are the ground and excited state geometry optimizations followed by normal modes calculations and calculations of the Franck-Condon vibronic integrals.
The time-dependent density functional theory (TD-DFT) with hybrid functionals is one of the most popular methods for electronic structure modelling of larger actinide complexes, as it is computationally less expensive than wave-function based methods. TD-DFT together with the CAM-B3LYP functional is able to reconcile the flaws in the determination of vertical excitation and emission energies, that was a challenging task for DFT several years ago.
As a benchmark system serving the purpose of assessing the accuracy of our theoretical protocol, the uranyl tetrachloride UO2Cl42- was selected because of the extensive amount of structural and spectroscopic data available [2]. A good agreement was found between ours and previously obtained theoretical data (structural parameters, orbitals nature, excitation energies) [3]; the final luminescence spectrum is in remarkable agreement with our TRLFS measurements. In the framework of this conference I will guide you through the various steps of the theoretical methodology, and illustrate how useful it is to assign recorded TRLFS spectra.
References
[1] J. Visnak and L. Sobec, EPJ Web of Conferences 128, 02002 (2016).
[2] R.G. Denning et al., Chem. Phys. Letters, 180, 101 (1991).
[3] K. Pierloot et al., J. Chem. Phys., 123, 204309 (2005).