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 (1) and [Ir­(pbt)₂(aipm)]­Cl (2) have been synthesized based on the ligands aip = 2-(9-anthryl)-1H-imidazo­[4,5-f]­[1,10]­phenanthroline, aipm = 2-(9-anthryl)-1-methyl-imidazo­[4,5-f]­[1,10]­phenanthroline, and pbtH = 2-phenylbenzothiazole in order to explore both the influence of the substituent group R₁ (R₁ = H in 1 and CH₃ in 2) on photo-oxidation activity and photo-oxidation-induced luminescence. Both ¹H NMR spectra and ES mass spectra indicate that the anthracene moiety in complex 1 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 1, complex 2 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 1 and 2 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.