Carborane Tuning Optical Properties Of Triphenylamine And Organometallic Iridium(?) Derivatives

Dicarba-closo-dodecaboranes have been used as versatile building blocks for construction of functional materials and pharmaceuticals owing to their useful properties such as thermal stability, unique structures and electronic effects, enriched boron content and low bio-toxicity for decades. Among these applications, the optical properties of carborane-based materials have been attracting a lot of attention. The previous reports have demonstrated that carboranes, based on the carbon substitution,could tune the photophysical properties in solutions upon linked to ?-conjugated systems utilizing their unique electronic and steric effects. However, less examples is about the carborane boron substitution or the two-photon absorption properties.Furthermore, there is no report about the effects of carboranes on the optical properties of supramolecular systems through non-covalent interactions, although lots of carborane-based derivatives have been proved that they could form the hydrogen bondings.To enable those diverse applications, structural modifications of carboranes have been the first concern. Substitution at carbon was readily achieved by deprotonation of C-H as early as the discovery of carborane. Substitution at boron remains much less explored owing to the less acidic B-H bonds. In particular, selective boron-functionalization at carborane cluster is still a synthetic challenge because of the chemically close B-H bonds and limited boron functional groups. This situation seriously restricts further exploration of advanced applications of carborane derivatives.Based on the previous reports, we use the 9-I-o-carborane (or 9-I-m-carborane)and 4-MgBrC6H4C2H3 as the starting materials in the presence of (Ph3P)2PdCl2,giving rise to the boron-substituted derivatives with terminal alkene group. Similar,after deprotonation, the carborane were used to react with 4-iodo-phenylethylene,leading to the carbon-substituted terminal alkene derivatives. Then, terminal alkene carborane-based derivatives were connected to the triphenylamine via the Heck cross coupling reaction, leading to the carbon and boron substitutions, respectively. Based on the experimental data,we found that these carborane-based tribranched compounds not only have good properties in one-photon fluorescence, but also show excellent two-photon properties, no matter which isomer of carborane (o- or m- carborane), or which position (carbon- or boron-substitution). The m-carborane carbon-substituted ones, in particular, showed the largest TPA cross section (a = 511 GM) among the reported carborane derivatives (p-carborane-based 1D non-linear fluorescent compounds had the highest ?= 470 GM). m-Carborane carbon-substituted ones have good quality cell images with bright intracellular luminescence, owing to the large TPA cross section and no significant cytotoxicity of. More importantly, the high-quality two-photon fluorescence 3D imagings have been also obtained. To our best knowledge, this is the first example of two-photon fluorescence 3D imaging of carborane derivative.As what we have discussed previously the C-H hydrogens in the C2B10H12 isomers have acidic (pKa = 22.0 for o-, 25.6 for m-, 26.8 forp-) character, and most of cabon substitutions were prepared after deprotonation, which also indicate the potential for hydrogen-bonding interactions as the hydrogen bond donor group. A series of phosphorescent ionic iridium(?) complexes with 2,2'-bipyridyl ligands functionalized by different carborane isomers have been obtained. Various anions,such as BF4-, PF6-, SbF6-, OTf-, ClO4-, NO3-, BPh4-, F- and Cl- as the counterions,have been involved. We hope to extend the carborane to the supermolecular systems and to tune the optical properties by the interactions between the cations and the anions.We developed a new and effective synthetic method for the preparation of carborane-based 2,2'-bipyridyl derivatives starting from C-formyl-o-carborane (or C-formyl-m-carborane, C-formyl-p-carborane) and 4,4'-dimethyl-2,2'-bipyridine. The target compounds can be obtained efficiently through the deprotonation of 4,4'-dimethyl-2,2'-bipyridine to its dilithium salt and subsequent reaction with C-formyl-carborane through dehydration. Then the carborane-based ligands coordinated with iridium, leading to new carborane-based Ir? complexes. As revealed by X-ray crystallography, cations components formed twisted cavities and the counterions were fixed into the cavities by the hydrogen bonds, on the contrary, the non-carborane-substituted one do not display the ordered packing diagram. The introduction of carborane can improve significantly the luminescence in solid state,and the variation tendency of the luminescence intensity is in accordance with the hydrogen-bond accepting ability of anions. Meanwhile, the size of counterions also can tune the phosphorescence intensity. In conclusion, the binding strength of anion-hydrogen bond Ccar-H…X is the key affecting factor of the intensity of the phosphorescence in solid state. Of course, the characteristic rigidity and steric hindrance of carborane also play important roles in promoting the ordered packing.