An investigation on the second-order NLO properties of novel cationic cyclometallated Ir(III) complexes of the type [Ir(2-phenylpyridine)₂(9-R-4,5-diazafluorene)]⁺ (R = H, fulleridene) and the related neutral complex with the new 9-fulleriden-4-monoazafluorene ligand

Novel cationic cyclometallated Ir(III) complexes bearing diaza- or monoazafluorene substituted or not with a C60-fullerene moiety have been synthesized together with a novel interesting ligand 9-fulleriden-4-monoazafluorene and the related Ir(III) neutral complex [Ir(ppy)2(9-fulleriden-4-monoazafluorene)]. All complexes show a negative large value of μβ_1.907 (−600 to −2190 × 10⁻⁴⁸ esu), as determined by the Electric Field Induced Second Harmonic generation (EFISH) technique working at 1.907 μm in 10⁻³ M CH₂Cl₂ solution. The NLO response increases upon introduction of the fullerene moiety, due to a decrease of the interaction forces between the anion and cation within the ion pair which leads to an increase of the percentage of free ions, as evidenced by diffusion NMR experiments. Besides, it appeared that for the neutral complex [Ir(ppy)₂(9-fulleriden-4-monoazafluorene)] the EFISH μβ_1.907 value is lower than that of cationic Ir(III) complexes, but comparable or slightly lower to the values of other neutral Ir(III) complexes such as [Ir(ppy)2(RCOCR′COR)] (ppy = cyclometallated 2-phenylpyridine; R = Me, Ph; R′ = H, 2,4-dinitrophenyl), confirming that the second-order NLO response of these neutral chromophores is dominated by ILCT processes concerning cyclometallated 2-phenylpyridines.