Two Anthracene-Based Ir(III) Complexes [Ir(pbt)₂(aip)]Cl and [Ir(pbt)₂(aipm)]Cl: Relationship between Substituent Group and Photo-oxidation Activity as Well as Photo-oxidation-Induced Luminescence

Two anthracene-based complexes [Ir­(pbt)₂(aip)]Cl (<b>1</b>) and [Ir­(pbt)₂(aipm)]­Cl (<b>2</b>) have been synthesized based on the ligands aip = 2-(9-anthryl)-1<i>H</i>-imidazo­[4,5-<i>f</i>]­[1,10]­phenanthroline, aipm = 2-(9-anthryl)-1-methyl-imidazo­[4,5-<i>f</i>]­[1,10]­phenanthroline, and pbtH = 2-phenylbenzothiazole in order to explore both the influence of the substituent group R₁ (R₁ = H in <b>1</b> and CH₃ in <b>2</b>) on photo-oxidation activity and photo-oxidation-induced luminescence. Both ¹H NMR spectra and ES mass spectra indicate that the anthracene moiety in complex <b>1</b> can be oxidized at room temperature upon irradiation with 365 nm light. Thus, this complex shows photo-oxidation-induced turn-on yellow luminescence. Compared to <b>1</b>, complex <b>2</b> incorporates an R₁ = CH₃ group, resulting in very weak photo-oxidation activity. On the basis of experimental results and quantum chemical calculation, we report the differences between <b>1</b> and <b>2</b> in both photo-oxidation behavior and the related luminescence modulation and discuss the relationship between photo-oxidation activity and substituent group R₁ in these complexes.