Deep-red circularly polarised luminescent C70 derivatives

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.

Near‐Infrared‐Absorbing Chiral Open [60]Fullerenes

“…This is suggestive of double bond characters both for C(1)À C(a) and C(a)À N bonds. Upon seeing the bond lengths, this structure could be described as a resonance hybrid consisting of neutral (I) and zwitterionic (II) states whereas the contribution of III is negligible since the bond length of C(b)=O(b) is comparable to that of C(c)=O(c), being consistent with the observed 13 C chemical shifts in which the signals of C(1) and C(a) appeared at δ 109.80 and 149.07 ppm, respectively (Figure 4b).…”

“…This type of dissymmetry usually appears in fullerenes and bowl‐shaped molecules, thus being so‐called as fullerene chirality [9] . Even achiral [60]fullerene might gain the chirality depending upon an addition pattern and identification of addends [10–13] . For instance, a non‐inherently chiral functionalization pattern was shown in Figure 1 where 1,7‐adduct [14] becomes C 1 ‐chiral when the two substituents are unidentified.…”

“…[9] Even achiral [60]fullerene might gain the chirality depending upon an addition pattern and identification of addends. [10][11][12][13] For instance, a non-inherently chiral functionalization pattern was shown in Figure 1 where 1,7-adduct [14] becomes C 1 -chiral when the two substituents are unidentified. Another functionalization pattern, e.g., 1,23-adduct, [15] causes an inherent chirality even if the addends are identical (C 2 -symmetry).…”

Near‐Infrared‐Absorbing Chiral Open [60]Fullerenes

“…This type of dissymmetry usually appears in fullerenes and bowl‐shaped molecules, thus being so‐called as fullerene chirality [9] . Even achiral [60]fullerene might gain the chirality depending upon an addition pattern and identification of addends [10–13] . For instance, a non‐inherently chiral functionalization pattern was shown in Figure 1 where 1,7‐adduct [14] becomes C 1 ‐chiral when the two substituents are unidentified.…”

Chiral Open-[60]Fullerene Ligands with Giant Dissymmetry Factors

“…Despite the most abundant [60]­fullerene being achiral, it could readily attain an inherent chirality by an appropriate functionalization pattern on its spherical π surface. Thereby, the fullerene chirality has been thrust into the spotlight, and excellent chiroptical features of fullerene-based materials have been found in succession over the past few years . For instance, in 2020, Tajima and co-workers achieved an enantiomorphic crystallization of organic semiconducting molecules in thin films using chiral methano[60]­fullerenes as surface modifiers .…”