Chloride, Bromide, and Iodide Photooxidation in Acetonitrile/Water Mixtures Using Binuclear Iridium(III) Photosensitizers

Simon De Kreijger; Benjamin Elias; Ludovic Troian-Gautier

doi:10.1021/acs.inorgchem.3c02648

Chloride, Bromide, and Iodide Photooxidation in Acetonitrile/Water Mixtures Using Binuclear Iridium(III) Photosensitizers

Inorg Chem. 2023 Oct 2;62(39):16196-16202. doi: 10.1021/acs.inorgchem.3c02648. Epub 2023 Sep 21.

Authors

Simon De Kreijger¹, Benjamin Elias¹, Ludovic Troian-Gautier¹

Affiliation

¹ Institut de la Matière Condensée et des Nanosciences (IMCN), Molecular Chemistry, Materials and Catalysis (MOST), UCLouvain, Place Louis Pasteur 1, Box L4.01.02, B-1348 Louvain-la-Neuve, Belgium.

PMID: 37734153
DOI: 10.1021/acs.inorgchem.3c02648

Abstract

Two iridium(III) binuclear photosensitizers, [Ir(dFCF₃ppy)₂(N-N)Ir(dFCF₃ppy)₂]²⁺, where N-N is tetrapyrido[3,2-a:2',3'-c:3″,2″-h:2‴,3‴-j]phenazine (Ir-TPPHZ) and 1,4,5,8-tetraazaphenanthrene[9,10-b]-1,4,5,8,9,12-hexaazatriphenylene (Ir-TAPHAT) are reported for iodide, bromide, and chloride photooxidation in acetonitrile and acetonitrile/water mixtures using blue-light irradiation. Excited-state reduction potentials E_red* of +2.02 and +2.09 V vs NHE were determined for Ir-TPPHZ and Ir-TAPHAT, respectively. Both photosensitizers' excited states were efficiently quenched by iodide, bromide, and chloride with quenching rate constants in the (3.5-9.2) × 10¹⁰ and (0.0036-2.9) × 10¹⁰ M^-1 s^-1 ranges in neat acetonitrile and acetonitrile/water mixtures, respectively. Nanosecond transient absorption spectroscopy provided unambiguous evidence of reductive excited-state electron transfer, with all halides in the solvent mixtures containing up to 50% water. Cage-escape yields were large (55-96%) in acetonitrile and dropped below 32% in 50:50 acetonitrile/water mixtures.