Neutral and Cationic Re(I) Complexes with Pnictogen-Based Coligands and Tunable Functionality: From Phosphorescence to Photoinduced CO Release.

In this work, we have explored Re(I) complexes featuring triphenylpnictogen (, = , , or )-based coligands and bidentate (neutral or monoanionic) luminophores derived from 1,10-phenantroline (), as well as from 2-(3-(-butyl)-1-1,2,4-triazol-5-yl)pyridine (). The effect of the increasingly heavy elements on the structural parameters, photoexcited-state properties, and electrochemical behavior as well as the hybridization defects and polarization of the atoms was related to the charges of the main luminophores (i.e., vs ) and explored in terms of photoluminescence spectroscopy, X-ray diffractometry, and quantum-chemical methods. Therefore, an in-depth analysis of the bonding, crystal packing, excited-state energies, and lifetimes was assessed in liquid solutions, frozen glassy matrices, and crystalline phases along with a semiquantitative photoactivation study. Notably, by changing the main ligand from to , an increase in radiative and radiationless deactivation rates ( and , respectively) at 77 K together with a faster photoinduced CO release and fragmentation at room temperature was detected. In addition, a progressively red-shifted phosphorescence was observed with the growing atomic number of the pnictogen atom, along with a boost in and at 77 K. Down the V main group and upon coordination of the atom to the Re(I) center, an increasingly prominent jump of s-orbital participation on the binding sp-orbitals of the atoms is evidenced. Based on these findings, the ability of these complexes to act as tunable photoluminescent labels able to perform as light-driven CO-releasing molecules is envisioned.