Deactivation of Excited States in Transition‐Metal Complexes: Insight from Computational Chemistry

Abstract

Investigation of the excited-state decay dynamics of transition-metal systems is a crucial step for the development of photoswitchable molecular based materials with applications in growing fields as energy conversion, data storage, or molecular devices. The photophysics of these systems is an entangled problem arising from the interplay of electronic and geometrical rearrangements that take place on a short time scale. Several factors play a role in the process: various electronic states of different spin and chemical character are involved, the system undergoes important structural variations and several nonradiative processes can occur. Computational chemistry is a useful tool to get insight into the microscopic description of the photophysics of these materials, since it provides unique information about the character of the electronic spin states involved, the energetics and time evolution of the system. In this review article, we present an overview of the state of the art methodologies available to address the several aspects that have to be incorporated to properly describe the deactivation of excited states in transition-metal complexes. The most recent developments in theoretical methods are discussed and illustrated with examples.

Controlling the Lifetime of the Triplet MLCT State in Fe(II) Polypyridyl Complexes through Ligand Modification

“…A graphical representation of the active orbitals is given in Figures S3 and S4 of the Supplementary Information. This choice of active space is the standard CAS for transition metal complexes in general [49,50] and has been successfully applied in complexes with spin crossover closely related to the ones treated here [10,64]. Since we are not after highly accurate relative energies, we have used basis sets of moderate size.…”

Finding intersections between electronic excited state potential energy surfaces with simultaneous ultrafast X-ray scattering and spectroscopy

“…13,15,31 Theoretical calculations have assisted in assessing the viability of alternative relaxation mechanisms. [32][33][34][35][36] Initial studies concluded that a sequential relaxation mechanism involving a 3 MC should dominate, 35 but more recent studies indicate direct 3 MLCT relaxation to the 5 MC excited state may compete with the sequential mechanism. 32,33 The sensitivity of the second-order spin-orbit coupling magnitude to the specic geometry of the [Fe(bpy) 3 ] 2+ in the 3 MLCT excited state found by Sousa and coworkers 32,33 demonstrates the need for direct dynamics simulations to theoretically determine the relative importance of the direct and sequential mechanisms.…”

Band-selective dynamics in charge-transfer excited iron carbene complexes

“…[24][25][26] Experimental progress together with increasingly advanced quantum chemical calculations and dynamics simulations have yielded a wealth of valuable insight into the ultrafast early deactivation dynamics in such complexes. [27][28][29][30][31] In the last ve years, a new ligand motif featuring strongly sigma-donating Nheterocyclic carbenes (NHCs) has been realized synthetically and demonstrated through a combination of time-resolved optical characterization and calculations to achieve dramatically improved excited state properties of iron complexes. 32,33 This has provided a promising path for development also of iron-based photosensitizers for a variety of photoinduced electron transfer applications.…”