Unprecedented Ir(III) cationic complexes based on tridentate tetrazolate ligands: synthesis, photophysics and encapsulation in SiO2 nanoparticles

Abstract

The first examples of luminescence Ir(III) complexes derived from a tridentate tetrazole ligand, 2-(tetrazole- 5-yl)-1,10-phenanthroline (Hphenttz), are reported here. Two cationic complexes, heteroleptic [Ir(tpy) (phenttz)]2+ (1) (tpy = 2,20:60,200-terpyridine) and homoleptic [Ir(phenttz)2]+(2), have been synthesized and fully characterized from a chemical, structural and photophysical point of view. Both complexes exhibit green luminescence with a prevalent 3LC (Ligand-Centered) character, which is evidenced by their structured emission profiles and low kr values (of about 103 s 1), and supported by density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations. In air-equilibrated solutions, 1 and 2 show emission lifetimes (respective values of 1.6 ms and 1.2 ms) comparable to that of the reference complex [Ir(tpy)2]3+ (1.0 ms) and quantum yields slightly lower (1.5% (1), 1.3% (2)) than that obtained for [Ir(tpy)2]3+ (2.5%). Under an oxygen-free atmosphere, the emission lifetimes and quantum yields (t/F) of the complexes increase significantly up to 5 ms/4.2% (1) and 3 ms/3.3% (2). 1 has been embedded within amorphous silica nanoparticles leading to the hybrid material 1@SiO2. This material shows enhanced photochemical stability and higher luminescence efficiency compared to the free complex, which demonstrates that silica hampers the diffusion of O2, restrains the mobility of the complex and stimulates the radiative decay of the excited state.