An Increase in\nthe Rigidity of the Environment Favors\nMLCT over the MC State in [Ru(bpy)<sub>2</sub>(Nicotine)<sub>2</sub>](Cl)<sub>2</sub>: A Case Study of Photolabile Ligands

Ru(II)-complexes with photolabile ligands find a wide\nrange of\napplications, e.g., in drug release and in the design of light-responsive\ninterfaces. While light-driven ligand loss has been studied mechanistically\nin detail for complexes in solution, comparably few studies are present\nthat investigate the process in a material context, i.e., in a rigid\nenvironment and in the absence of solvent. This paper adds to this\nunderrepresented perspective by studying the excited-state dynamics\nof [Ru(bpy)<sub>2</sub>(nicotine)<sub>2</sub>] (Cl)<sub>2</sub> (<b>Ru-nico</b>) as a model system in poly(methyl methacrylate) (PMMA)\nand polyacrylonitrile (PAN) matrices. Femtosecond transient absorption\nspectroscopy and time-resolved emission spectroscopy are employed\nto monitor the photodissociation of labile nicotine ligands in polymer\nenvironments. Photoexcitation within the metal-to-ligand charge transfer\n(MLCT) band leads to transient dissociation of the nicotine ligand\nwhen the complex is dissolved in water. However, optical excitation\nof the <sup>1</sup>MLCT transition of the complexes embedded in polymer\nmatrices does not result in photodissociation, likely due to the rigidity\nof the environment, which cannot solvate the undercoordinated complex\nafter ligand dissociation and the dissociated ligand. These insights\nshed light on the role of the local environment when considering the\nphotophysics of ligand loss from Ru(II)-polypyridyl complexes and,\nhence, their use in the light-activation of reactive molecular components\nin materials.