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Photophysical Properties of Spirobifluorene-Based o-Carboranyl Compounds Altered by Structurally Rotating the Carborane Cages.


ABSTRACT: 9,9'-Spirobifluorene-based o-carboranyl compounds C1 and C2 were prepared and fully characterized by multinuclear nuclear magnetic resonance (NMR) spectroscopy and elemental analysis. The solid-state structure of C1 was also determined by single-crystal X-ray diffractometry. The two carboranyl compounds display major absorption bands that are assigned to ?-?* transitions involving their spirobifluorene groups, as well as weak intramolecular charge-transfer (ICT) transitions between the o-carboranes and their spirobifluorene groups. While C1 only exhibited high-energy emissions (?em = ca. 350 nm) in THF at 298 K due to locally excited (LE) states assignable to ?-?* transitions involving the spirobifluorene group alone, a remarkable emission in the low-energy region was observed in the rigid state, such as in THF at 77 K or the film state. Furthermore, C2 displays intense dual emissive patterns in both high- and low-energy regions in all states. Electronic transitions that were calculated by time-dependent-DFT (TD-DFT) for each compound based on ground (S0) and first-excited (S1) state optimized structures clearly verify that the low-energy emissions are due to ICT-based radiative decays. Calculated energy barriers that are based on the relative energies associated with changes in the dihedral angle around the o-carborane cages in C1 and C2 clearly reveal that the o-carborane cage in C1 rotates more freely than that in C2. All of the molecular features indicate that ICT-based radiative decay is only available to the rigid state in the absence of structural fluctuations, in particular the free-rotation of the o-carborane cage.

SUBMITTER: Kim S 

PROVIDER: S-EPMC6891568 | biostudies-literature | 2019 Nov

REPOSITORIES: biostudies-literature

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Photophysical Properties of Spirobifluorene-Based <i>o</i>-Carboranyl Compounds Altered by Structurally Rotating the Carborane Cages.

Kim Seonah S   So Hyunhee H   Lee Ji Hye JH   Hwang Hyonseok H   Kwon Hyoshik H   Park Myung Hwan MH   Lee Kang Mun KM  

Molecules (Basel, Switzerland) 20191115 22


9,9'-Spirobifluorene-based <i>o</i>-carboranyl compounds <b>C1</b> and <b>C2</b> were prepared and fully characterized by multinuclear nuclear magnetic resonance (NMR) spectroscopy and elemental analysis. The solid-state structure of <b>C1</b> was also determined by single-crystal X-ray diffractometry. The two carboranyl compounds display major absorption bands that are assigned to <i>π</i>-<i>π</i>* transitions involving their spirobifluorene groups, as well as weak intramolecular charge-transf  ...[more]

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