Teaching Inorganic Photophysics and Photochemistry with Three Ruthenium(II) Polypyridyl Complexes: A Computer-Based Exercise

Among computational methods, DFT (density functional theory) and TD-DFT (time-dependent DFT) are widely used in research to describe, inter alia, the optical properties of transition metal complexes. Inorganic/physical chemistry courses for undergraduate students treat such methods, but quite often only from the theoretical point of view. In the calculation exercise herein described, students are guided step by step through the computational study of the photophysics and photochemistry of polypyridyl Ru(II) d6-metal complexes. In particular, by means of DFT and TD-DFT calculations, they are asked to examine and interpret a set of experimental data describing the absorption, emission, and photochemical behavior of three structurally related ruthenium complexes, namely, [Ru(bpy)3]2+ (1), [Ru(tpy)2]2+ (2), and [Ru(bpy)2(py)2]2+ (3). These complexes are particularly suitable for an educational purpose since they exhibit distinct optical and photochemical properties despite being structurally akin to each other. In the computational chemistry laboratory, the instructor progressively guides students through the preparation of DFT and TD-DFT inputs and the use of software for the analysis of output files, including visualization of optimized geometries, absorption spectra, orbitals, and spin density surfaces. The exercise covers training of students in several key concepts concerning the photophysics and photochemistry of transition metal complexes. These include Franck-Condon transitions and the role of 3MLCT (metal-to-ligand charge transfer) and 3MC (metal-centered or ligand-field) states in luminescence and ligand photodissociation processes. Notably, the mixed character of this exercise allows its integration with theoretical and experimental activities and the design of truly multidisciplinary courses.