Lawrence T. Scott

Gas-phase production and photoelectron spectroscopy of the smallest fullerene,C20

Fullerenes are graphitic cage structures incorporating exactly twelve pentagons. The smallest possible fullerene is thus C20, which consists solely of pentagons. But the extreme curvature and reactivity of this structure have led to doubts about its existence and stability. Although theoretical calculations have identified, besides this cage, a bowl and a monocyclic ring isomer as low-energy members of the C20 cluster family, only ring isomers of C20 have been observed so far. Here we show that the cage-structured fullerene C20 can be produced from its perhydrogenated form (dodecahedrane C20H 20) by replacing the hydrogen atoms with relatively weakly bound bromine atoms, followed by gas-phase debromination. For comparison we have also produced the bowl isomer of C20 using the same procedure. We characterize the generated C20 clusters using mass-selective anion photoelectron spectroscopy; the observed electron affinities and vibrational structures of these two C20 isomers differ significantly from each other, as well as from those of the known monocyclic isomer. We expect that these unique C20 species will serve as a benchmark test for further theoretical studies.

A short, rigid, structurally pure carbon nanotube by stepwise chemical synthesis.

The inaccessibility of uniform-diameter, single-chirality carbon nanotubes (CNTs) in pure form continues to thwart efforts by scientists to use these ultrathin materials in innovative applications that could revolutionize nanoscale electronics. Stimulated by the challenge to address this long-standing problem, we and other organic chemists have envisioned a new production strategy involving the controlled elongation of small hydrocarbon templates, such as hemispherical nanotube end-caps, prepared by bottom-up chemical synthesis; the diameter and rim structure encoded in the template would dictate the diameter and chirality of the resulting CNT. Toward that objective, a short [5,5] CNT has now been synthesized by stepwise chemical methods. This C(50)H(10) geodesic polyarene has been isolated, purified, crystallized, and fully characterized by NMR spectroscopy, UV-vis absorption spectroscopy, high resolution mass spectrometry, and X-ray crystallography.

Hole-Transporting Materials with a Two-Dimensionally Expanded π-System around an Azulene Core for Efficient Perovskite Solar Cells

Two-dimensionally expanded π-systems, consisting of partially oxygen-bridged triarylamine skeletons that are connected to an azulene (1-3) or biphenyl core (4), were synthesized and characterized. When tetra-substituted azulene 1 was used as a hole-transporting material (HTM) in perovskite solar cells, the observed performance (power conversion efficiency = 16.5%) was found to be superior to that of the current HTM standard Spiro-OMeTAD. A comparison of the hole mobility, the ability to control the HOMO and LUMO levels, and the hole-collection efficiency at the perovskite/HTM interface in 1 with reference compounds (2-4 and Spiro-OMeTAD) led to the elucidation of key factors required for HTMs to act efficiently in perovskite solar cells.

New Strategies for Synthesizing Short Sections of Carbon Nanotubes

“Bent and battered benzene rings” have captivated organic chemists since the middle of the last century. Most commonly, the bending is enforced by bridging the para (or meta) positions of benzene with short chains of atoms to produce “cyclophanes”. 2] The degree of bending depends inversely on the length of the tether, and these strained macrocycles sometimes contain more than one bridged benzene ring. Cyclophanes incorporating bent naphthalene units or even larger polyarenes have also been prepared. In recent months, one of the highest unclimbed pinnacles in this field was finally conquered, and shortly thereafter, the impressive record for bending was resoundingly shattered. Figure 1 depicts the new cyclophanes that have recently rocked this venerable branch of chemistry. The scientists responsible for their synthesis have noted the structural features that these compounds share with carbon nanotubes (Figure 1), and they are already contemplating ways to extend their successes toward the rational, chemical synthesis of carbon nanotubes. The first of these recent breakthroughs was reported in late 2008 by Bertozzi and co-workers. As newcomers to cyclophane chemistry, this creative team conceived a fresh strategy for synthesizing macrocycles composed entirely of para-substituted benzene rings. Implementing the plan required a novel solution to one particularly challenging latestage transformation, but, ultimately, they prepared and spectroscopically characterized three members of the previously unknown family of [N]cycloparaphenylenes (CPP-9, CPP-12, and CPP-18 ; N = 9, 12, and 18, respectively). Besides solving one of the longest standing problems in cyclophane chemistry, this synthesis is also remarkable for its brevity: only five steps were required to assemble the fully aromatized macrocycles from 1,4-diiodobenzene (Scheme 1). The syn-selective addition of 4-iodophenyllithium to parabenzoquinone provided the key building block (1), from which the final target molecules were all assembled. A portion of 1 was converted into the corresponding diboronate (2), and Suzuki coupling of 1 with 2 gave macrocycles 3a, 3b,

Carbon nanotubes from short hydrocarbon templates. Energy analysis of the Diels–Alder cycloaddition/rearomatization growth strategy

Molecular orbital calculations at the AM1 and B3LYP/6–31G* levels of theory have been used to analyze the Diels–Alder cycloaddition/rearomatization strategy for growing uniform diameter, single-chirality carbon nanotubes from short hydrocarbon templates (aromatic belts and hemispherical end-caps) by metal-free chemical methods. Bay regions on the rim of a [10,10]nanotube end-cap (15) are predicted to exhibit Diels–Alder reactivity comparable to that of bay regions in planar polyarenes that have previously been transformed into new benzene rings by reactions with “masked acetylene” dienophiles. The Diels–Alder reactivity of nanotube template rims was found to be relatively unaffected by the presence or absence of a cap on the other end.

Fragments of fullerenes and carbon nanotubes : designed synthesis, unusual reactions, and coordination chemistry

PREFACE vii FOREWORD xi CONTRIBUTORS xiii ACRONYMS xvii 1 MOLECULAR CLIPS AND TWEEZERS WITH CORANNULENE PINCERS 1 Andrzej Sygula and Willard E. Collier 2 SYNTHESIS OF BOWL-SHAPED AND BASKET-SHAPED FULLERENE FRAGMENTS VIA BENZANNULATED ENYNE---ALLENES 41 Kung K. Wang, Hu Cui, and Bo Wen 3 ANIONS OF BUCKYBOWLS 63 David Eisenberg, Roy Shenhar, and Mordecai Rabinovitz 4 CURVED p-CONJUGATED STABLE OPEN-SHELL SYSTEMS POSSESSING THREE-DIMENSIONAL MOLECULAR/ELECTRONIC SPIN STRUCTURES 95 Yasushi Morita and Akira Ueda 5 EXPERIMENTAL AND CALCULATED PROPERTIES OF FULLERENE AND NANOTUBE FRAGMENTS 135 Derek R. Jones, Praveen Bachawala, and James Mack 6 COORDINATION PREFERENCES OF BOWL-SHAPED POLYAROMATIC HYDROCARBONS 157 Alexander S. Filatov and Marina A. Petrukhina 7 SUMANENES: SYNTHESIS AND COMPLEXATION 187 Toshikazu Hirao and Toru Amaya 8 r-BONDED TRANSITION METAL COMPLEXES OF POLYCYCLIC AROMATIC CARBON COMPOUNDS 205 Paul R. Sharp 9 HEMISPHERICAL GEODESIC POLYARENES: ATTRACTIVE TEMPLATES FOR THE CHEMICAL SYNTHESIS OF UNIFORM-DIAMETER ARMCHAIR NANOTUBES 235 Anthony P. Belanger, Katharine A. Mirica, James Mack, and Lawrence T. Scott 10 AROMATIC BELTS AS SECTIONS OF NANOTUBES 259 Gaston R. Schaller and Rainer Herges 11 CYCLOPARAPHENYLENES: THE SHORTEST POSSIBLE SEGMENTS OF ARMCHAIR CARBON NANOTUBES 291 Xia Tian and Ramesh Jasti 12 CONJUGATED MOLECULAR BELTS BASED ON 3D BENZANNULENE SYSTEMS 311 Masahiko Iyoda, Yoshiyuki Kuwatani, Tohru Nishinaga, Masayoshi Takase, and Tomohiko Nishiuchi 13 TOWARD FULLY UNSATURATED DOUBLE-STRANDED CYCLES 343 Malte Standera and A. Dieter Schl uter 14 BENT PYRENES: SPRINGBOARDS TO AROMATIC BELTS? 367 Graham J. Bodwell, Gandikota Venkataramana, and Unikela Kiran Sagar INDEX 401

Modeling of Supramolecular Properties of Molecular Tweezers, Clips, and Bowls

Abstract The electrostatic potential surface (EPS) is calculated for molecular tweezers, clips, and bowls at different levels of theory (semiempirical AM1, ab initio HF/6-31G*, and density functional theory pBP/DN**). According to these calculations, the molecular electrostatic potential (MEP) on the concave side of the molecular tweezers and clips is suprisingly negative for hydrocarbons. This finding seems to be a general phenomenon in nonconjugated π-electron systems with concave-convex topology and it explains the receptor properties of the molecular tweezers and clips. Analogous calculations performed for the conjugated aromatic molecular bowls show different results. The DFT calculations predict that in these systems the more negative MEP lies on the concave side similar to the findings for the nonconjugated molecular tweezer- and clip-systems, whereas the AM1 calculation leads to the opposite result that the MEP is more negative on convex side of the bowl-systems.

Foregoing rigidity to achieve greater intimacy.

Interactions between the surfaces of planar and nonplanar molecules have generated considerable interest in materials chemistry as critical elements for understanding twodimensional supramolecular assembly, molecular and chiral recognition, and heterogeneous catalysis. Carbon-rich balland bowl-shaped polyaromatic molecules, such as fullerenes and fullerene fragments or buckybowls, figure prominently in these studies. Fullerenes have been found to form solid constructs with planar metalloporphyrins with remarkably close contacts but without the need for matching their convex and concave faces. Molecular self-organization of nonplanar polyaromatic bowls on a planar metal surface introduces the interesting additional factor of symmetry mismatch. Studies of ordered structures formed by weakly bound corannulene, C20H10, on the Cu(110) surface examined by scanning tunneling microscopy (STM) have revealed interesting insights into their molecular interactions. However, the overall effect of these interactions on the geometry of the corannulene bowl could not be evaluated by the STM method. In this work, we selected a system that allowed us to investigate the mutual structural influences of bowl-shaped polyarenes and a planar polynuclear metal unit upon their attractive interaction (Figure 1). Curving of the planar

Pyrolytic production of fullerenes

Abstract Recently, we have shown that [60] fullerene (C 60 ) may be produced by pyrolysis of the bowl-shaped corannulene molecule under a wide range of conditions. Both naphthalene and its dimer benzo [ k ] fluoranthene may be employed as precursors to C 60 .

HRMS directly from TLC slides. A powerful tool for rapid analysis of organic mixtures.

High-resolution mass spectra (HRMS) of individual spots on thin-layer chromatography (TLC) slides can now be obtained quickly and easily at atmospheric pressure, with zero sample preparation, using commercially available instrumentation. The method is complementary to GC-mass spectrometry but is not limited to compounds of high volatility and high thermal stability. TLC-HRMS can be used to monitor chemical reactions in real time and has the capacity thereby to accelerate significantly the pace of synthetic organic chemistry.