Deboronation-Induced Ratiometric Emission Variations of Terphenyl-Based --Carboranyl Compounds: Applications to Fluoride-Sensing.

--carboranyl compounds bearing the -type perfectly distorted or planar terphenyl rings (- and -, respectively) and their -derivatives (- and -, respectively) were synthesized and fully characterized using multinuclear NMR spectroscopy and elemental analysis. Although the emission spectra of both -compounds exhibited intriguing emission patterns in solution at 298 and 77 K, in the film state, - mainly exhibited a π-π* local excitation (LE)-based emission in the high-energy region, whereas - produced an intense emission in the low-energy region corresponding to an intramolecular charge transfer (ICT) transition. In particular, the positive solvatochromic effect of - and theoretical calculation results at the first excited (S) optimized structure of both -compounds strongly suggest that these dual-emissive bands at the high- and low-energy can be assigned to each π-π* LE and ICT transition.

Planarity of terphenyl rings possessing o-carborane cages: turning on intramolecular-charge-transfer-based emission.

To clarify the relationship between planarity and intramolecular charge transfer (ICT), two o-carboranyl compounds (TCB and FCB) containing different ortho-type terphenyl rings, namely, perfectly distorted or planar phenyl rings, were synthesised and fully characterised. Although the emission spectra of both compounds presented intriguing dual-emission patterns in solution at 298 or 77 K and in the film state, distorted TCB mostly showed locally excited emission, whereas planar FCB demonstrated intense emission corresponding to an ICT transition. Interestingly, the emission efficiencies and radiative decay constants of terphenyl-based o-carboranyl compounds were gradually enhanced by increasing the planarity of the terphenyl groups.