Cyclometalated Ir^III Complexes with Substituted 1,10‐Phenanthrolines: A New Class of Efficient Cationic Organometallic Second‐Order NLO Chromophores

Abstract

Cyclometalated cationic Ir(III) complexes with substituted 1,10-phenanthrolines (1,10-phen), such as [Ir(ppy)(2)(5-R-1,10-phen)]Y (ppy=cyclometalated 2-phenylpyridine; R=NO(2), H, Me, NMe(2); Y(-)=PF(6) (-), C(12)H(25)SO(3) (-), I(-)) and [Ir(ppy)(2)(4-R,7-R-1,10-phen)]Y (R=Me, Ph) are characterized by a significant second-order optical non linearity (measured by the electrical field induced second harmonic generation (EFISH) technique). This nonlinearity is controlled by MLCT processes from the cyclometalated Ir(III), acting as a donor push system, to pi* orbitals of the phenanthroline, acting as an acceptor pull system. Substitution of cyclometalated 2-phenylpyridine by the more pi delocalized 2-phenylquinoline (pq) or benzo[h]quinoline (bzq) or by the sulfur-containing 4,5-diphenyl-2-methyl-thiazole (dpmf) does not significantly affect the mubeta absolute value, which instead is affected by the nature of the R substituents on the phenanthroline, the higher value being associated with the electron-withdrawing NO(2) group. By using a combined experimental (the EFISH technique and (1)H and (19)F PGSE NMR spectroscopy) and theoretical (DFT, time-dependent-DFT (TDDFT), sum over states (SOS) approach) investigation, evidence is obtained that ion pairing, which is controlled by the nature of the counterion and by the concentration, may significantly affect the mubeta values of these cationic NLO chromophores. In CH(2)Cl(2), concentration-dependent high absolute values of mubeta are obtained for [Ir(ppy)(2)(5-NO(2)-1,10-phen)]Y if Y is a weakly interacting anion, such as PF(6) (-), whereas with a counterion, such as C(12)H(25)SO(3) (-) or I(-), which form tight ion-pairs, the absolute value of mubeta is lower and quite independent of the concentration. This mubeta trend is partially due to the perturbation of the counterion on the LUMO pi* levels of the phenanthroline. The correlation between the mubeta value and dilution shows that the effect of concentration is a factor that must be taken into careful consideration.

Cu(I) hybrid inorganic–organic materials with intriguing stimuli responsive and optoelectronic properties

“…Such values are much larger than the one previously obtained for 125a in agreement with an increase in the π-delocalization on the bipyridine ligands induced by the phenyl substituents. A similar observation was previously reported for iridium and ruthenium complexes featuring substituted phenanthroline ligands [148,149].…”

The synthesis of tetrahedral bipyridyl metallo-octupoles with large second- and third-order nonlinear optical properties

“…These data clearly show the large quadratic NLO activity of these new multipolar chromophores. As previously observed for donor-substituted bipyridine metal complexes [54], the quadratic NLO response increases with the response can be reasonably attributed to an increase in the pdelocalization on the bipyridine ligands induced by the phenyl substituents, a feature that has also been observed in the case of iridium and ruthenium complexes featuring substituted phenanthroline ligands [55,56]. The two-photon absorption cross-sections were measured using either the TPEF (two-photon excited fluorescence) method for fluorescent compounds or using the open aperture Z-scan technique for non emissive ones.…”

Carborane tuning on iridium complexes: redox-switchable second-order NLO responses

“…In recent years, a few reports have appeared in the literature on NLO properties determined by the electric field induced second harmonic generation (EFISH) method and theoretical approaches [16][17][18][19][20]. Notably, Valore et al [21,22] reported that the presence of various charge transfer (CT) processes between the Ir(III) metal center and phenanthrolines ligands also produced a promising NLO response. Meanwhile, inorganic materials have attracted considerable attention as candidates for secondorder NLO materials [23][24][25].…”