Synthesis and Characterisation of New Cationic Fluorinated Iridium(III) Complexes via Quaternisation of Tetrazole‐based Ancillary Ligands: A Convenient Approach for Fine‐tuning Photophysical Properties and Antimicrobial Activity

Herein we report the synthesis and characterisation of heteroleptic cationic Ir(III) complexes, [Ir(ppy) 2 (PyTz‐ R )][PF 6 ] and [Ir(ppy) 2 (iQTz‐ R )][PF 6 ], (ppy: 2‐phenylpyridine, PyTz: 2‐(1 H ‐tetrazol‐5‐yl)pyridine, iQTz: 1‐(1 H ‐tetrazol‐5‐yl)iso‐quinoline and R : ─CH 3 , ─CHF 2 , ─CH 2 CF 3 or ─CH 2 Ph‐ p ‐CF 3 ). The parent Ir(ppy) 2 (PyTz) and Ir(ppy) 2 (iQTz) complexes were converted to the cationic derivatives by regiospecific tetrazole quaternisation adopting “chemistry‐on‐a‐complex” and “ligand‐first” approaches. Structures were confirmed by NMR/FTIR spectroscopies, mass spectrometry, and single‐crystal X‐ray crystallography. DFT was used to probe electronic changes upon quaternisation. Absorption spectra were broadly similar across all complexes (strong UV bands with weaker 300–450 nm MLCT features), whereas cationisation markedly altered emission: the neutral complexes showed vibronically structured emission (iQTz red‐shifted vs PyTz), while all cationic derivatives displayed broad, structureless, further red‐shifted profiles. The bathochromic shift increased with the electron‐withdrawing strength of the R group (─CHF 2 > ─CH 2 CF 3 > ─CH 2 Ph‐ p ‐CF 3 ≈ ─CH 3 ). The photoluminescence quantum yields for the cationic complexes were determined to be in the range of 3.3‐11.2%. The thermal stability of the complexes was evaluated by thermogravimetric analysis. Finally, the cationic complexes were qualitatively assessed for potential antimicrobial activity against E. coli and S. aureus , with activity observed against S. aureus in well‐diffusion experiments.