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

Abstract

Much effort has been devoted to investigating the molecular geometries, electronic structures, redox properties and nonlinear optical (NLO) properties of Ir complexes involving o-, m- or p-carborane groups by density functional theory (DFT) methods. Switchable second-order NLO properties were induced by redox processes involving these complexes, and it was found that mainly the coordination bonds of Ir complexes changed during the oxidation process. Our calculations revealed that oxidation reactions have a significant influence on the second-order NLO response owing to the change in charge transfer pattern. The β tot values of oxidized species are at least ∼9 times larger for set I and ∼5 times larger for set II than those of the corresponding parent complexes. Introduction of carborane groups into ppy (phenylpyridine) ligands can enhance the second-order NLO response by 1.2- 1.6 times by a metal-to-ligand charge transfer (MLCT) transition between the Ir atom and carborane. The β tot of complex 2 [(ppy)2Ir(phen)](+) (phen = phenanthroline) is 3.3 times larger than that of complex 1 (ppy)2Ir(acce) (acce = acetylacetonate), which is caused by ligand-to-ligand charge transfer (LLCT) between ppy ligands and the ancillary ligand. Therefore, it can be concluded that the second-order NLO response can be effectively enhanced by oxidation reactions.

A trip in the nonlinear optical properties of iridium complexes

“…Whereas efficient second-order NLO switches have been reported in the case of ruthenium [17,18,99], zinc [40,55,100], platinum [82,83,[101][102][103], nickel [102], and palladium [102] complexes, to the best of our knowledge no example has been reported involving iridium complexes. Nevertheless, iridium complexes, which have abundant valence states and rich electrochemical properties, could be excellent second-order NLO redox-switch molecular materials, as suggested by recent theoretical investigations [104][105][106].…”

“…Oxidation of 29 and 30 caused a large enhancement of the second-order NLO activity (by a factor of 9 and 5, respectively), suggesting that it is possible to reach a large NLO contrast by redox processes [104].…”

“…The redox-switchable second-order NLO responses of various heteroleptic iridium(III) complexes bearing acetylacetonate ( 29) or 1,10-phenanthroline (30) as the ancillary ligand and two cyclometalated 2-phenylpyridines (29a, 30a) or substituted analogs bearing ortho (29b, 30b) meta (29c, 30c) or para (29d, 30d) carborane groups (Fig. 13) were studied using DFT methods [104]. As expected for the family of 1,10-phenanthroline-containing complexes (see Tables 3 and 6), a higher quadratic hyperpolarizability was calculated for the family of complexes 30 than for the family of complexes 29.…”

Cyclometalated Ir(III) Complexes with Curcuminoid Ligands as Active Second-Order NLO Chromophores and Building Blocks for SHG Polymeric Films

“…In the field of nonlinear optics, iridium complexes characterized by luminescent and NLO properties are fascinating as multifunctional molecular materials [58,59], as some of them have a versatile NLO redox-switching response [60,61]. In particular, those with two cyclometalated 2-phenylpyridine ligands (ppy) and a β-diketonate ancillary ligand, known for their luminescence and two-photon absorption properties [62], are of particular interest because they are characterized by a large second-order NLO response in solution [63].…”

An Unprecedented Family of Luminescent Iridium(III) Complexes Bearing a Six-Membered Chelated Tridentate C^N^C Ligand

“…0.1 Å) than the Ir−Cl bond in other cyclometalated tridentate Ir(III) complexes. 29,31,32,36,37,40,41 Given the short Ir−C C^N^C bonds [2.048(13) and 2.064(6) Å for 1, 2.028(4) and 2.031(3) Å for 2, and 2.017 (7) and 2.027 Å for 3], this leads also to a correspondingly shorter Ir−N C^N^C bond [2.055(11) Å for 1, 2.044(3) for 2, and 2.032(7) Å for 3] compared to the Ir− N dtBubpy bonds [2.158 (10) Electrochemical Properties. The electrochemical behavior for 1−3 was evaluated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV) in deaerated CH 2 Cl 2 solution at 298 K at a scan rate of 50 mV s −1 using Fc/Fc + as the internal reference and referenced with respect to SCE.…”