Tuning the Optical Properties of 2‐Thienylpyridyl Iridium Complexes through Carboranes and Anions

Abstract

2-Thienylpyridyl iridium(III) complexes containing an o-, m-, or p-carboranylvinyl-2,2'-bipyridine ligand and various counteranions (denoted o-PF6, m-BF4, m-PF6, m-SbF6, m-ClO4, m-OTf, m-NO3, m-BPh4, m-F, m-Cl, and p-PF6) were synthesized by using C-formyl carboranes as starting materials. The solid-state structures of o-PF6, m-PF6, m-ClO4, and m-BF4 showed that the cations form twisted cavities in which the anions are fixed by multiple hydrogen bonds. Anion-hydrogen interactions were investigated for nine m-carborane-based complexes with different counteranions. All carborane-based iridium(III) complexes show similar phosphorescence yields in solution but significantly different emission in the solid state. Anion-exchange titration and theoretical calculations revealed the relationships between structures and optical properties. The size of the anion and C-H⋅⋅⋅X anion-hydrogen bonds strongly influence the phosphorescence quantum yield in the solid state. In particular, the Ccar-H⋅⋅⋅X hydrogen bonds between the carboranyl unit and the anion play an important role in solid-state phosphorescence. Complex p-PF6 was successfully applied in phosphorescence-lifetime bioimaging owing to its low toxicity and near-infrared emission.

Carboranes as a Tool to Tune Phosphorescence

“…Most recently, Zhao and co‐workers provided a new strategy to tune the photophysical properties of iridium(III) complexes by simply changing the counterion . Yan and co‐workers used carboranes and anions to tune the optical properties of 2‐thienylpyridyl iridium(III) complexes ( 20 , 21 , and 22 ) (Scheme ) . The introduction of carborane isomers causes an approximately 50 nm red shift in the emission in solution (Table ).…”

“…The lifetime increases from 260 ns (21 % O 2 ) to 380 ns (2.5 % O 2 ), which makes it a potential probe for hypoxia imaging. Since the emission of the carborane‐functionalized 2‐thienylpyridyl iridium(III) complexes is close to the near‐infrared region, complex 22 with a long emission lifetime has also been successfully applied in phosphorescence lifetime imaging …”

Modulation of the cis‐ and trans‐Conformations in Bis‐o‐carborane Substituted Benzodithiophenes and Emission Enhancement Effect on Luminescent Efficiency by Solidification

“…One promising platform to overcome the ACQ problem is a class of aggregation-induced emission (AIE)-active boron complexes, which show significant emission not in the dilute state but in aggregation. [22][23][24][25][26][27][28][29][30][31][32][33][34] We have also focused on the arylmodified o-carboranes as a scaffold for constructing luminescent "element-block", [35,36] which is defined as a minimum functional unit composed of heteroatoms. [4] Additionally, based on environment-responsive intensity changes of the AIE-active materials, various types of film-type luminescent materials and sensors can be fabricated.…”

Enhancement of Aggregation-Induced Emission by Introducing Multiple o-Carborane Substitutions into Triphenylamine

“…o -Carborane [ 5 , 6 , 7 , 8 , 9 , 10 ] is an icosahedral cluster composed of 2 carbon and 10 boron atoms, and it has recently attracted attention as a key component for constructing solid-state luminescent materials [ 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 ]. Because of the electron-deficient nature of the boron cluster, intense emission from the intramolecular charge transfer (ICT) state can be observed from the donor–acceptor system with electron-donating units such as triphenylamine and its structural analogues [ 23 , 24 , 25 , 26 ].…”