Cationic cyclometallated iridium(III) complexes with substituted 1,10-phenanthrolines: the role of the cyclometallated moiety on this new class of complexes with interesting luminescent and second order non linear optical properties

The luminescence and second order non linear optical (NLO) response of [Ir(ttpy)(2)(5-R-1,10-phen)][PF6] (ttpy = cyclometallated 3'-(2-pyridil)-2,2':5',2aEuro(3)-terthiophene, phen = phenanthroline; R = Me, NO2) and [Ir(pq)(2)(5-R-1,10-phen)][PF6] (pq = cyclometallated 2-phenylquinoline) have been investigated experimentally in CH2Cl2 solution and compared with that of [Ir(ppy)(2)(5-R-1,10-phen)][PF6] (ppy = cyclometallated 2-phenylpyridine), characterized by one of the highest second order NLO response ever reported for a metal complex. Substitution of ppy with the more pi-delocalized pq does not affect significantly the luminescence and NLO properties. A slightly lower NLO response and a much poorer luminescence is observed for the related complexes with ttpy. In these complexes, DFT/TDDFT calculations show that the presence of ttpy induces a significant downshift of the HOMO energy, compared to ppy and pq. The NLO response is dominated by intense MLCT excited states, which are also assigned as originating the emission.