Exploring the Threshold between Fullerenes and Nanotubes: Characterizing Isomerically Pure, Empty-Caged, and Tubular Fullerenes D_5h-C₉₀ and D_5d-C₁₀₀

Abstract

We report the fully fledged photophysical characterization of isomerically pure, empty-caged, tubular fullerenes D 5h -C 90 and D 5d -C 100 and compare their key properties. In particular, the focus was on cage sizes between 60 and 150 carbon atoms with D 3 , D 3d/h , and D 5d/h symmetry. The optical band gap of D 5d -C 100 is 1.65 eV, which is larger than 1.37 eV of D 5h -C 90 . In stark contrast to the nonluminescent D 5h -C 90 , D 5d -C 100 luminesces at room temperature. Transient absorption spectroscopy shows that photoexcited D 5d -C 100 is subject to a slow intersystem crossing that generates a triplet excited state. In contrast, a fast, nonradiative internal conversion governs the deactivation of D 5h -C 90 : In this case, exploring the corresponding triplet excited state required triplet−triplet sensitization experiments with anthracene. Density functional theory calculations revealed the electronic structure of the fullertubes, and calculations are consistent with our experimental findings. The calculated band gap systematically decreases with the number of carbon atoms within the D 3 and D 3d/h series. In contrast, an oscillating behavior is noted within the series of D 5d/h fullertubes. Finally, photoexcited D 5d -C 100 was found to undergo hole transfer with electron-donating triethylamines readily but not electron transfer with electron-accepting methyl viologens.

Vibrational anatomy of C90, C96, and C100 fullertubes: probing Frankenstein's skeletal structures of fullerene head endcaps and nanotube belt midsection

“…14 Thus, all studied fullertubes have considerable gaps exceeding at least 1.5-2 eV. The spectra closely resemble those reported in the literature 5,10,11,15 thus confirming the structural identity of studied molecules.…”

“…In the experimental Raman spectrum it is detected as the medium-intensity feature at 1447 cm −1 . Another C 100 vibration with the large weight of the pentagonal pinch mode is A 1g (15) predicted at 1493 cm −1 . Here the cap and the belt parts contribute equally, each represented by a totally symmetric mode, A g (2) for C 60 and A 1g (2) for CNT.…”

“…On the hand, the study of the electronic properties of fullertubes with (5,5) and (9, 0) CNTs fragments concluded that the convergence is far from reach in realistic fullerene sizes and requires much longer tubes. 14,15 In this work, we will address this problem from the point of view of vibrational spectroscopy as the latter played a fundamental role in the studies of nanocarbon materials, from the very first indication of C 60 presence in the carbon soot confirmed by IR spectroscopy 16 to resonance Raman techniques which became indispensable for CNTs and graphene. [17][18][19] Force constants usually vanish over several bonds and therefore vibrations can be considered as more local than electronic excitations.…”

Gigantic C120 Fullertubes: Prediction and Experimental Evidence for Isomerically Purified Metallic [5,5] C120-D5d(1) and Nonmetallic [10,0] C120-D5h(10766)

“…In 2021, a study showed a transition to metallic properties by inserting 10 carbon atoms from the shorter [5,5] C 90 -D 5h (1) fullertube to the longer [5,5] C 100 -D 5d (1) fullertube. In 2022, an excited state study of [5,5] C 90 -D 5h (1) fullertubes showed photophysical properties consistent with classical fullerenes. However, the longer [5,5] C 100 -D 5d (1) fullertube broke the trend expected for fullerene behavior and suggested unique properties for C 100 fullertubes.…”

“…In 2022, an excited state study of [5,5] C 90 -D 5h (1) fullertubes showed photophysical properties consistent with classical fullerenes. However, the longer [5,5] C 100 -D 5d (1) fullertube broke the trend expected for fullerene behavior and suggested unique properties for C 100 fullertubes. A separate study in 2022 evaluated the catalytic behavior of fullertubes .…”