Abstract
Optically active fullerenes, including C60 and C70 derivatives carrying organic substituents, are used in a range of applications because of their unique spectroscopic, catalytic, and chiral recognition properties. However, their inherent photoexcited chirality is yet to be elucidated because of their very poor fluorescence quantum yield (Φf). We synthesised a new chiral C70 derivative, X70A, with 20% yield, by reacting bis-borylated xanthene with C70 in a one-step double addition reaction, followed by a successful optical resolution. The isolation of two separate X70A enantiomers was confirmed by mirror-image circular dichroism spectroscopy in the range of 300–750 nm. In toluene, the enantiomeric pair of X70A clearly revealed mirror-image circularly polarised luminescence (CPL) spectra with a high |glum| value of 7.0 × 10−3 at 690 nm. The first fullerene-based deep-red CPL of X70A should provide a new guideline for the design of chiral nanocarbon materials.
Highlights
Active fullerenes, including C60 and C70 derivatives carrying organic substituents, are used in a range of applications because of their unique spectroscopic, catalytic, and chiral recognition properties
Achiral buckminsterfullerene (C60) and [5,6]-fullerene ( C70) adopt highly symmetrical spherical and elliptical structures, respectively, allowing them to be utilised as n-type molecular semiconductors and building blocks of molecular conductors/magnets owing to the uniqueness of their energetically low-lying lowest unoccupied molecular orbitals (LUMOs)[1,2]
We report the first deep-red mirror-image circularly polarised luminescence (CPL) spectra at 690 nm, originating from a pair of chiral fullerene derivatives, which are associated with the corresponding mirror-image circular dichroism (CD)
Summary
Active fullerenes, including C60 and C70 derivatives carrying organic substituents, are used in a range of applications because of their unique spectroscopic, catalytic, and chiral recognition properties. Their inherent photoexcited chirality is yet to be elucidated because of their very poor fluorescence quantum yield (Φf). Nanocarbon materials that exhibit a large dissymmetry factor over long wavelength regions, such as the deep-red region, have rarely been investigated This is due to the fact that the molecular design that can simultaneously achieve chirality and an effective π-conjugation whose absorption reaches the deep-red region is still unexplored. We believe that the results obtained for this CPL-exhibiting X70A will provide useful guidelines for the future material design of nanocarbon light-emitting materials that emit in the deep-red to near infrared (NIR) region with high g-values[26,27,28]
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