Sc₂C₂@<i>D</i>_3<i>h</i>(14246)‑C₇₄: A Missing Piece of the Clusterfullerene Puzzle

Clusterfullerenes with variable carbon cages have been extensively studied in recent years. However, despite all these efforts, C₇₄ cage-based clusterfullerene remains a missing piece of the puzzle. Herein, we show that single-crystal X-ray crystallographic analysis unambiguously assigns the previously reported dimetallofullerene Sc₂@C₇₆ to a novel carbide clusterfullerene, Sc₂C₂@<i>D</i>_3<i>h</i>(14246)-C₇₄, the first experimentally proven clusterfullerene with a C₇₄ cage. In addition, Sc₂C₂@<i>D</i>_3<i>h</i>(14246)-C₇₄ was charaterized by mass spectrometry, ultraviolet–visible–near-infrared absorption spectroscopy, ⁴⁵Sc nuclear magnetic resonance, and cyclic voltammetry. Comparative studies of the motion of the carbide cluster in Sc₂C₂@<i>D</i>_3<i>h</i>(14246)-C₇₄ and Sc₂C₂@C_2<i>n</i> (<i>n</i> = 40−44) revealed that a combination of factors, involving both the shape and size of the cage, is crucial in dictating the cluster motion. Moreover, structural studies of <i>D</i>_3<i>h</i>(14246)-C₇₄ revealed that it can be easily converted to <i>C</i>_<i>s</i>(10528)-C₇₂ and <i>T</i>_<i>d</i>(19151)-C₇₆ cages via C₂ desertion/insertion and Stone–Wales transformation. This suggests that <i>D</i>_3<i>h</i>(14246)-C₇₄ might play an important role in the growth pathway of clusterfullerenes

A Metallofullerene Electron Donor that Powers an Efficient Spin Flip in a Linear Electron Donor–Acceptor Conjugate

The dream target of artificial photosynthesis is the realization of long-lived radical ion pair states that power catalytic centers and, consequently, the production of solar fuels. Notably, magnetic field effects, especially internal magnetic field effects, are rarely employed in this context. Here, we report on a linear Lu₃N@<i>I</i>_<i>h</i>-C₈₀–PDI electron donor–acceptor conjugate, in which the presence of the Lu₃N cluster exerts an appreciable electron nuclear hyperfine coupling on the charge transfer dynamics. As such, a fairly efficient radical ion pair intersystem crossing converts the initially formed singlet radical ion pair state, ¹[(Lu₃N@<i>I</i>_<i>h</i>-C₈₀)^•+–PDI^•–], to the corresponding triplet radical ion pair state, ³[(Lu₃N@<i>I</i>_<i>h</i>-C₈₀)^•+–PDI^•–]. Most notably, the radical ion pair state lifetime of the latter is nearly 1000 times longer than that of the former

Popular C₈₂ Fullerene Cage Encapsulating a Divalent Metal Ion Sm²⁺: Structure and Electrochemistry

Two Sm@C₈₂ isomers have been well characterized for the first time by means of ¹³C NMR spectroscopy, and their structures were unambiguously determined as Sm@<i>C</i>_<i>2v</i><i>(9)</i>-C₈₂ and Sm@<i>C</i>_<i>3v</i><i>(7)</i>-C₈₂, respectively. A combined study of single crystal X-ray diffraction and theoretical calculations suggest that in Sm@<i>C</i>_<i>2v</i><i>(9)</i>-C₈₂ the preferred Sm²⁺ ion position shall be located in a region slightly off the <i>C</i>₂ axis of <i>C</i>_<i>2v</i><i>(9)</i>-C₈₂. Moreover, the electrochemical surveys on these Sm@C₈₂ isomers reveal that their redox activities are mainly determined by the properties of their carbon cages

WO_<i>x</i>@PEDOT Core–Shell Nanorods: Hybrid Hole-Transporting Materials for Efficient and Stable Perovskite Solar Cells

PEDOT-coated WO_<i>x</i> nanorodes (NRs) were prepared for the first time by simply stirring WO_<i>x</i> nanowires (NWs) with 3,4-ethylenedioxythiophene (EDOT) in aqueous solution. A series of spectroscopic characterizations indicate that the polymerization of EDOT occurrs not only on the surface but also along the [010] planes of WO_<i>x</i> NW, resulting in the truncation of long WO_<i>x</i> NW to produce WO_<i>x</i>@PEDOT NRs with abundant oxygen vacancies. Furthermore, WO_<i>x</i>@PEDOT NRs were used to prepare a hole transport layer (HTL) in planar p–i–n perovskite solar cells (PeSCs). The WO_<i>x</i>@PEDOT-based devices yielded a comparable average power conversion efficiency (PCE) of 12.89% with improved open-circuit voltage (<i>V</i>_OC) and fill factor (FF) but lower short-circuit current density (<i>J</i>_SC), as compared to the devices with conventional PEDOT:PSS (12.88%). The observed device performance is mainly attributed to the better perovskite texture on the WO_<i>x</i>@PEDOT HTL, improved energy alignment, and suppressed charge recombination at the WO_<i>x</i>@PEDOT/perovskite interface as well as lower charge conductivity of the WO_<i>x</i>@PEDOT HTL. In addition, the PeSCs based on WO_<i>x</i>@PEDOT-doped PEDOT:PSS showed remarkably improved PCEs up to 14.73%, which may be ascrible to the combined merit of WO_<i>x</i>@PEDOT NRs and PEDOT:PSS. More impressively, benefiting from the inherent neutral nature of WO_<i>x</i>@PEDOT NRs, WO_<i>x</i>@PEDOT-based devices exhibited obviously improved stability compared to that with PEDOT:PSS HTL. These results thus demonstrate a path toward the development of new hybrid nanostructures for efficient and stable PeSCs

A Simple Perylene Derivative as a Solution-Processable Cathode Interlayer for Perovskite Solar Cells with Enhanced Efficiency and Stability

A simple alcohol-soluble perylene derivative (i.e., tetramethylammonium salt of perylene-3,4,9,10-tetracarboxylic acid; TMA-PTC) was prepared and applied as a cathode interlayer (CIL) to modify the PC₆₁BM/Ag interface in planar p–i–n perovskite solar cells (PeSCs). As a result, the power conversion efficiency (PCE) of the TMA-PTC-based PeSCs is ca. 30% higher than that of the devices without CIL. It was revealed that the enhancement in PCE might be attributed to the improved electron-transporting and hole-blocking properties of the PC₆₁BM/TMA-PTC/Ag interfaces. Moreover, the TMA-PTC devices show remarkably higher stability than those without CIL probably due to the suppressed corrosion of perovskite on Ag cathode. Our findings thus demonstrate a multifunctional and solution-processable CIL that may be a promising block for the fabrication of low-cost, high-efficiency and stable planar p–i–n PeSCs

Sm@<i>C</i>_2<i>v</i>(19138)‑C₇₆: A Non-IPR Cage Stabilized by a Divalent Metal Ion

Although a non-IPR fullerene cage is common for endohedral cluster fullerenes, it is very rare for conventional endofullerenes M@C_2<i>n</i>, probably because of the minimum geometry fit effect of the endohedral single metal ion. In this work, we report on a new non-IPR endofullerene Sm@<i>C</i>_2<i>v</i>(19138)-C₇₆, including its structural and electrochemical features. A combined study of single-crystal X-ray diffraction and DFT calculations not only elucidates the non-IPR cage structure of <i>C</i>_2<i>v</i>(19138)-C₇₆ but also suggests that the endohedral Sm²⁺ ion prefers to reside along the C₂ cage axis and close to the fused pentagon unit in the cage framework, indicative of a significant metal–cage interaction, which alone can stabilize the non-IPR cage. Furthermore, electrochemical studies reveal the fully reversible redox behaviors and small electrochemical gap of Sm@<i>C</i>_2<i>v</i>(19138)-C₇₆, which are comparable to those of IPR species Sm@<i>D</i>_3<i>h</i>-C₇₄

Sc₂O@<i>C</i>_3<i>v</i>(8)‑C₈₂: A Missing Isomer of Sc₂O@C₈₂

By introducing CO₂ as the oxygen source during the arcing process, a new isomer of Sc₂O@C₈₂, Sc₂O@<i>C</i>_3<i>v</i>(8)-C₈₂, previously investigated only by computational studies, was discovered and characterized by mass spectrometry, UV–vis–NIR absorption spectroscopy, cyclic voltammetry, ⁴⁵Sc NMR, density functional theory (DFT) calculations, and single-crystal X-ray diffraction. The crystallographic analysis unambiguously elucidated that the cage symmetry was assigned to <i>C</i>_3<i>v</i>(8) and suggests that Sc₂O cluster is disordered inside the cage. The comparative studies of crystallographic data further reveal that the Sc1–O–Sc2 angle is in the range of 131.0–148.9°, much larger than that of the Sc₂S@<i>C</i>_3<i>v</i>(8)-C₈₂, demonstrating a significant flexibility of dimetallic clusters inside the cages. The electrochemical studies show that the electrochemical gap of Sc₂O@<i>C</i>_3<i>v</i>(8)-C₈₂ is 1.71 eV, the largest among those of the oxide cluster fullerenes (OCFs) reported so far, well correlated with its rich abundance in the reaction mixture of OCF synthesis. Moreover, the comparative electrochemical studies suggest that both the dimetallic clusters and the cage structures have major influences on the electronic structures of the cluster fullerenes. Computational studies show that the cluster can rotate and change the Sc–O–Sc angle easily at rather low temperature

Facile Synthesis of an Extensive Family of Sc₂O@C_2<i>n</i> (<i>n</i> = 35–47) and Chemical Insight into the Smallest Member of Sc₂O@<i>C</i>₂(7892)–C₇₀

An extensive family of oxide cluster fullerenes (OCFs) Sc₂O@C_2<i>n</i> (<i>n</i> = 35–47) has been facilely produced for the first time by introducing CO₂ as the oxygen source. Among this family, Sc₂O@C₇₀ was identified as the smallest OCF and therefore isolated and characterized by mass spectrometry, ⁴⁵Sc nuclear magnetic resonance, UV–vis–near-infrared absorption spectroscopy, cyclic voltammetry, and density functional theory calculations. The combined experimental and computational studies reveal a non-isolated pentagon rule isomer Sc₂O@C₂(7892)–C₇₀ with reversible oxidative behavior and lower bandgap relative to that of Sc₂S@<i>C</i>₂(7892)–C₇₀, demonstrating a typical example of unexplored OCF and underlining its cluster-dependent electronic properties

Isomeric Sc₂O@C₇₈ Related by a Single-Step Stone–Wales Transformation: Key Links in an Unprecedented Fullerene Formation Pathway

It has been proposed that the fullerene formation mechanism involves either a top-down or bottom-up pathway. Despite different starting points, both mechanisms approve that particular fullerenes or metallofullerenes are formed through a consecutive stepwise process involving Stone–Wales transformations (SWTs) and C₂ losses or additions. However, the formation pathway has seldomly been defined at the atomic level due to the missing-link fullerenes. Herein, we present the isolation and crystallographic characterization of two isomeric clusterfullerenes Sc₂O@<i>C</i>_2<i>v</i><i>(3)</i>-C₇₈ and Sc₂O@<i>D</i>_3<i>h</i><i>(5)</i>-C₇₈, which are closely related via a single-step Stone–Wales (SW) transformation. More importantly, these novel Sc₂O@C₇₈ isomers represent the key links in a well-defined formation pathway for the majority of solvent-extractable clusterfullerenes Sc₂O@C_2<i>n</i> (<i>n</i> = 38–41), providing molecular structural evidence for the less confirmed fullerene formation mechanism. Furthermore, DFT calculations reveal a SWT with a notably low activation barrier for these Sc₂O@C₇₈ isomers, which may rationalize the established fullerene formation pathway. Additional characterizations demonstrate that these Sc₂O@C₇₈ isomers feature different energy bandgaps and electrochemical behaviors, indicating the impact of SW defects on the energetic and electrochemical characteristics of metallofullerenes

Sc₂O@<i>C</i>_2<i>v</i>(5)‑C₈₀: Dimetallic Oxide Cluster Inside a C₈₀ Fullerene Cage

A new oxide cluster fullerene, Sc₂O@<i>C</i>_2<i>v</i>(5)-C₈₀, has been isolated and characterized by mass spectrometry, UV–vis–NIR absorption spectroscopy, cyclic voltammetry, ⁴⁵Sc NMR, DFT calculations, and single crystal X-ray diffraction. The crystallographic analysis unambiguously elucidated that the cage symmetry was assigned to <i>C</i>_2<i>v</i>(5)-C₈₀ and suggests that the Sc₂O cluster is ordered inside the cage. The crystallographic data further reveals that the Sc1–O–Sc2 angle is much larger than that found in Sc₂O@<i>T_d</i>(19151)-C₇₆ but almost comparable to that in Sc₂O@<i>C</i>_<i>s</i>(6)-C₈₂, suggesting that the endohedral Sc₂O unit is flexible and can display large variation in the Sc–O–Sc angle, which depends on the size and shape of the cage. Computational studies show that there is a formal transfer of four electrons from the Sc₂O unit to the C₈₀ cage, i.e., (Sc₂O)⁴⁺@(C₈₀)^4–, and the HOMO and LUMO are mainly localized on the C₈₀ framework. Moreover, thermal and entropic effects are seen to be relevant in the isomer selection. Comparative studies between the recently reported Sc₂C₂@C_2<i>v</i>(5)-C₈₀ and Sc₂O@<i>C</i>_2<i>v</i>(5)-C₈₀ reveal that, despite their close structural resemblance, subtle differences exist on the crystal structures, and the clusters exert notable impact on their spectroscopic properties as well as interactions between the clusters and corresponding cages