The role of 5-R-1,10-phenanthroline (R = CH3, NO2) on the emission properties and second-order NLO response of cationic Ir(III) organometallic chromophores

[Ir(cyclometallated 4,5-diphenyl-2-methyl-thiazole)2(5-R-1,10-phenanthroline)][PF6] (R = CH3, NO2) complexes were prepared and fully characterized, the structure of the complex with 5-CH3-1,10-phenanthroline being also determined by X-ray diffraction. The emission properties of both complexes have been investigated and their second-order nonlinear optical (NLO) response has been determined experimentally by the EFISH technique and found to be similar but slightly lower than that of related [Ir(ppy)2(5-R-1,10-phenanthroline)][PF6] (ppy = cyclometallated 2-phenylpyridine), characterized by one of the highest second-order NLO response ever reported for a metal complex. In the complexes, SOS/TDDFT calculations show that the large and negative sign of the measured hyperpolarizability is mainly due to the significant contribution of rather intense MLCT transitions involving the phenanthroline as acceptor ligand.