Effect of Planarity of Aromatic Rings Appended to o-Carborane on Photophysical Properties: A Series of o-Carboranyl Compounds Based on 2-Phenylpyridine- and 2-(Benzo[b]thiophen-2-yl)pyridine

Herein, we investigated the effect of ring planarity by fully characterizing four pyridine-based -carboranyl compounds. -Carborane was introduced to the C4 position of the pyridine rings of 2-phenylpyridine and 2-(benzo[ ]thiophen-2-yl)pyridine ( and , respectively), and the compounds were subsequently borylated to obtain the corresponding -chelated compounds and . Single-crystal X-ray diffraction analysis of the molecular structures of and confirmed that -carborane is appended to the aryl moiety. In photoluminescence experiments, , but not , showed an intense emission, assignable to intramolecular charge transfer (ICT) transition between the aryl and -carborane moieties, in both solution and film states. On the other hand, in both solution and film states, and demonstrated a strong emission, originating from π-π * transition in the aryl groups, that tailed off to 650 nm owing to the ICT transition. All intramolecular electronic transitions in these -carboranyl compounds were verified by theoretical calculations. These results distinctly suggest that the planarity of the aryl groups have a decisive effect on the efficiency of the radiative decay due to the ICT transition.