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

Abstract

In this work, we have explored Re(I) complexes featuring triphenylpnictogen (PnPh3, Pn = P, As, or Sb)-based coligands and bidentate (neutral or monoanionic) luminophores derived from 1,10-phenantroline (phen), as well as from 2-(3-(tertbutyl)-1H-1,2,4-triazol-5-yl)pyridine (H(N-tBu)). 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 Pn atoms was related to the charges of the main luminophores (i.e., phen vs NtBu) and explored in terms of photoluminescence spectroscopy, Xray 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 phen to N-tBu, an increase in radiative and radiationless deactivation rates (kr and knr, 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 kr and knr at 77 K. Down the Vth main group and upon coordination of the Pn atom to the Re(I) center, an increasingly prominent jump of s-orbital participation on the binding sxp3.00-orbitals of the Pn 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.