Department of Chemistry, University of Ulsan, Ulsan 44610, Republic of Korea.
Dalton Trans. 2018 Dec 11;47(48):17441-17449. doi: 10.1039/c8dt03771j.
A family of closo-carborane-appended luminophores (closo-OXD1-2 and closo-DPS1-2) in which 2-R-o-carboranes (R = H, Me) are attached to the diphenyl-1,3,4-oxadiazole (OXD) or diphenyl-sulfone (DPS) acceptor groups were prepared and characterized. Deboronation of the closo-carborane cage produced the corresponding nido-carboranyl luminophores (nido-OXD1-2 and nido-DPS1-2). Whereas the closo-compounds were poorly emissive in THF (ΦPL < 0.01), the nido-luminophores exhibited an intense fluorescence with good quantum yields (ΦPL = 0.1-0.45). Electrochemical studies showed that while the closo-OXD and -DPS compounds displayed only carborane-centred, quasi-reversible reduction, the nido-compounds exhibited the typical features for nido-carborane-centred, irreversible oxidation and acceptor-centred, reversible reduction. Theoretical studies suggested that while the 1ππ* state of closo-compounds is nonemissive due to the contribution of closo-carborane to the LUMO in the S1 excited state, the intramolecular charge transfer (ICT) state from the nido-carborane to acceptor moieties in nido-compounds leads to an efficient fluorescence. Finally, THF solutions of closo-OXD1 and -DPS1 showed strong fluorescence upon the addition of fluoride anions under mild heating, but were intact to other anions, including cyanide, allowing the selective OFF-ON fluorescence sensing of fluoride.
一种具有 closo-碳硼烷取代基的发光体（closo-OXD1-2 和 closo-DPS1-2）家族，其中 2-R-o-碳硼烷（R = H、Me）连接到二苯基-1,3,4-恶二唑（OXD）或二苯基砜（DPS）受体基团上。 closo-碳硼烷笼的脱硼化产生了相应的 nido-碳硼烷发光体（nido-OXD1-2 和 nido-DPS1-2）。 尽管 closo 化合物在 THF 中发射性差（ΦPL < 0.01），但 nido 发光体表现出强烈的荧光，具有良好的量子产率（ΦPL = 0.1-0.45）。 电化学研究表明，虽然 closo-OXD 和 -DPS 化合物仅显示碳硼烷中心、准可逆还原，但 nido 化合物表现出典型的 nido-碳硼烷中心、不可逆氧化和受体中心、可逆还原特征。 理论研究表明，尽管 closo 化合物的 1ππ* 态由于 closo-碳硼烷在 S1 激发态中对 LUMO 的贡献而没有发射，但 nido 化合物中 nido-碳硼烷到受体部分的分子内电荷转移（ICT）态导致有效的荧光。 最后，在温和加热下， closo-OXD1 和 -DPS1 的 THF 溶液在加入氟阴离子后显示出强烈的荧光，但对其他阴离子（包括氰化物）保持完整，允许选择性的 OFF-ON 荧光检测氟化物。
