Deboronation-Induced Turn-on Phosphorescent Sensing of Fluorides by Iridium(III) Cyclometalates with o-Carborane

Abstract

Heteroleptic tris-cyclometalated Ir(III) complexes bearing an o-carborane at the 4-or 5-position in the phenyl ring of the ppy ligand (closo-1 and -2) were prepared and characterized. The X-ray crystal structure of closo-1 reveals the fac arrangement of the three C ∧ N chelates around the Ir atom. Treatment of closo complexes with fluoride anions led to selective deboronation of the closo-carborane cage, producing the corresponding nido-carborane-substituted complexes (nido-1 and -2). Whereas closo-1 and -2 were almost nonemissive in THF, nido-1 and -2 were highly phosphorescent (Φ PL = 0.94−0.95). Theoretical studies suggested that, while the emission quenching in closo-1 can be ascribed to the substantial involvement of o-carborane in the 3 MLCT excited state, the intraligand charge transfer ( 3 ILCT) state from the nido-carborane to pyridyl moieties is responsible for the efficient phosphorescence in nido-1. The addition of fluoride to the buffered THF/H 2 O solution (1/1, v/v, pH 7) of closo-1 and -2 under mild heating led to strong emission intensity, allowing the turn-on phosphorescence detection of fluoride in aqueous medium at the ppb level.

Solid‐State Thermochromic Luminescence through Twisted Intramolecular Charge Transfer and Excimer Formation of a Carborane−Pyrene Dyad with an Ethynyl Spacer

“…Boron cluster compounds have recently attracted significant attention as a key component in the development of stimuli‐responsive luminescent solid films, which hold great promise as versatile sensors and probes . To obtain clear responses, such materials need to show dramatic luminochromism that is triggered by the target stimuli.…”

Spirobifluorene‐Based o‐Carboranyl Compounds: Insights into the Rotational Effect of Carborane Cages on Photoluminescence

“…The ICT‐based emission is not observed in nido ‐ SFC1 in the rigid states (at 77 K and in the film state). Indeed, deboronation of the o ‐carborane cage can lead to the alternation of the intramolecular electronic transitions, resulting in the dramatic changes of the emissive properties Accordingly, these phenomena demonstrate that the CT‐based emission can be quenched by the anionic character of nido ‐ o ‐carborane, which inhibits the ICT transitions.…”

“…This feature favors the radiative mechanism based on the ICT transition involving the o-carborane. The ICT-based emission is not observed in nido-SFC1 in the rigid states (at 77 Ka nd in the film state).I ndeed, deboronation of the o-carboranec age can lead to the alternation of the intramolecular electronic transitions, resulting in the dramatic changes of the emissive properties [52,53] Accordingly, these phenomena demonstrate that the CT-based emission can be quenched by the anionic character of nido-o-carborane, which inhibits the ICT transitions. Unlike SFC1,t he emission spectra of SFC2 exhibited dual emission patterns, whichc an be assigned to high-energyL E (l em = 371-373 nm) and low-energy ICT emissive bands (l em = 578 nm in THF, l em = 528 nm at 77 K, and l em = 538 nm in film state), respectively.I np articular, the ICT character of the lowenergy emissive bands was confirmed by the solvatochromic effect in solvents with different polarities (Table1 and Figure S11i nt he Supporting Information).…”

Boron‐Functionalized Phosphorescent Iridium(III) Complexes

“…Lee et al prepared heteroleptic tris(cyclometalate) Ir III complexes 30a and 30b (Scheme 4), each bearing one o-Cb group at either the m-or the p-position to the Ir-C bond. [38] These closo complexes underwent facile deboronation of the closo-Cb cage, producing the corresponding nido-Cb-substituted complexes nido-30a and nido-30b. Whereas 30a and 30b were almost non-emissive in THF (Table 3), nido-30a and nido-30b exhibited phosphorescence with very high quantum efficiency (Φ p = 0.94-0.95).…”