Guest Inclusion of Butadiyne-Bridged Macrocycles Tobe Lab. M1 Hiroshi Takeda

Contents ・ What is Macrocycles ・ Complexation of cyclothiophene with fullerene on a surface ・ My work ・ Summary 2

Macrocycles: Definition and Utilities Macrocycles are defined as any molecules having a ring of nine or more atoms. Macrocyclic natural products ⇒ Superior biochemical functionalities development as drugs 3 clarithromycin

Shape-Persistent Macrocycles In recent years, intense interest have been paid for π-conjugated in shape-persistent macrocycles ⅰ ) large, supramolecular building blocks that generate π-stacked structures in solution ⅱ ) noncollapsable nanoporous solids 4 In my laboratory syntheses and properties of the shape-persistent macrocycles consisting of aromatic rings and triple bonds have been reported. They showed self-association and binding to large organic substrate.

Host-Guest Chemistry Hosts and guests held together in solution in definable structural relationships by electrostatic forces (enthalpic component) Macrocycles (Host): Organic molecule containing convergent binding sites. Synthetic counterparts to receptor sites in enzymes, genes, antibodies and ionophores Guest: Molecules or ions containing divergent binding sites. Counterparts to substrates, inhibitors, cofactors, antigens 5

Complexation of Butadiyne-Bridged Pyridinophane with Ｔ ropylium Cation in Ｓ olution 6 R=C 8 H 17 To examine the binding ability of pyridinophanes 1 and 2, we choose tropylium ion was chosen as a guest. The chemical shift change of the aromatic protons of 1 and 2 on 1 H-NMR titration measurements with tropylium cation was analyzed and calculate for complex formation constant. tropylium ion 1 2

Complexation of Butadiyne-Bridged Pyridinophane with Tropylium Cation in Solution 7 R=C 8 H 17 On the basis of 1 H-NMR titration measurements, The nonlinear least-squares regression analysis gave K11(1:1) and K21(2:1) → For 1, K11 = 3×10 3 M -1 and K21 = 3×10 4 M -1 For 2, K11 = 1×10 2 M -1 and K21 = 4×10 2 M -1 The binding constants of 1 are larger than those of 2 →The size of the cavity of 1 is suitable for trapping of tropylium cation. > K11(1:1)K21(2:1) 13 × × × ×10 2 K is complex formation constant : 錯形成定数 1 2

Self-Assembly of Butadiyne-Bridged Pyridinophane 8

Scanning Tunneling Microscopy (STM) 9 Tunneling current electron Tunneling current Tip Sample Tip Sample

Guest Inclusion Ability of Butadiyne- Bridged Pyridinophane on Solid Surfaces 10 The brighter spots within the cavity of 1 are trapped tropylium cations. An empty macrocycle 1 ＋ R = COOC 8 H 17 1

Introduction of Paper 11 cyclo[12]thiophene fullerene Bu ≡ 〜

Previous work of Monolayer of C[12]T 12

Previous work of Monolayer of C[12]T 13 ・ The individual rings appeared in bright features ・ The interior cavity and the insulating alkyl side chains appeared darker in the image

Previous work of Monolayer of C[12]T 14 ・ The individual rings appeared in bright features ・ The interior cavity and the insulating alkyl side chains appeared darker in the image

Previous work of Monolayer of C[12]T 15 Top view Side view “spider-like” comformation

About Thiophene 16 Cyclic π-conjugated cyclothiophene self-assembles at the solid-liquid interface to form well-ordered 2D molecular network. C[12]T : cyclo[12]thiophene fullerenes C[12]T The formation of 1:1 donor–acceptor (D–A) complex p-type (donor) monolayer n-type (acceptor) material charge transfer interaction

Complexation of C[12]T-C ・ An isolated C 60 molecule (white arrow) adsorbed at the liquid/monolayer interface. ・ The electron-accepting C 60 formed a stable 1:1 D–A complex with cyclothiophene. ・ From Semiempirical calculations, the most stable complexation site is at the rim of the macrocycle Providing maximal π–π interaction.

Complexation of C[12]T-C 60 ・ Four individual C 60 fullerenes, labeled “C” (cavity) or “R” (rim), are adsorbed on top of a C[12]T monolayer. ・ A R-type fullerene is imaged brighter, the three C-type fullerenes can be observed as rather diffuse spots. 18

Complexation of C[12]T-C 60 During scanning, the C-type fullerenes were desorbed There are two types of fullerenes (R diameter ∼ 1 nm versus C diameter ∼ 1.6 nm) The C-type is not immobilized, but rather rotates around an axis perpendicular to the substrate. 19 a complexation site on top of the conjugated “rim”is stable position

Complexation of C[12]T-C Complexes with more than one fullerene per macrocycle were never seen The fullerenes interact with the cyclothiophenes at the same position and form perfectly ordered domains. The C[12]T monolayer acts as a veritable template The complexation ratio is exclusively 1:1.

The 1:1 D–A complex 21 ・ The electron density of macrocycle’s HOMO is drastically shifted by the complexation of C 60. ・ It becomes unfavorable when C 60 occupy the electron-deficient part of the C[12]T macrocycle. The macrocycle can form complex with fullerenes.

Scanning tunneling Spectroscopy (STS) 22 STS provides a useful tool in the study of the electrical properties of molecular monolayer. On the sample, it can detect the tunneling current by changing of the bias voltages, which probe the local density of electronic states (LDOS) and the band gap of surfaces and materials on surfaces at the atomic scale. The I(V) and dI/dV data refrect the conductivity of organic molecules may be changed in a variety of ways. dI/dV ∝ LDOS

The electrical properties of C[12]T 23 The asymmetric I–V curve was observed. The asymmetry is clearly seen in the differential curve (dI/dV–V) The frontier orbitals of the system were localized at -0.7 and 0.95 V, below and above the Fermi level, respectively. C[12]T C[12]T–C 60 complex C[12]T The general p-doping character of electron-rich thiophene compounds. HOMO–LUMO gap is 1.65 V. Relate to the local density of states (LDOS) of the molecule.

The electrical properties of C[12]T–C 60 complex 24 The shape of the I–V curve at positive bias is very similar to the non-complexed macrocycle. However at negative bias the current behavior is quite different. From the differential (dI/dV–V) curve, a bigger gap between the frontier orbitals (1.85 V) T he shift of the HOMO to higher voltages (–0.9 V) C[12]T C[12]T–C 60 complex The saturation of the current at negative bias is a special spectroscopic characteristic of the D–A complex. The typical exponential behavior of the tunneling current in semiconductors is blocked starting at a value of –1.06 V. C[12]T–C 60 complex

Summary self-assembled and highly ordered monolayers of macrocyclic thiophenes C[12]T can be used as template to epitaxially grow 3D nanoarchitectures with C60-fullerenes. Submolecularly resolved STM images allow the investigation of unique 1:1 complexes comprising a ring- shaped p-type and a spherical n-type semiconductor. The dynamics of C60 adsorption and the complexation site on the macrocycle have been analyzed by STM The electronic properties of the complexes have been elucidated by means of STS showing interesting saturation behavior in the I–V curves. 25

Purpose of My Work 26 ・ Formation of 2D molecular networks on the solid surface. ・ Guest inclusion ability toward larger guest molecule ・ Synthesis of butadiyne-bridged pyridinophane which possesses a larger cavity ・ Evaluation of its guest inclusion ability guest host -My purpose-

Purpose of My Work 27 ・ Synthesis of butadiyne-bridged pyridinophane which possesses a larger cavity ・ Evaluation of its guest inclusion in solution and on surface.

Synthesis of Butadiyne-Bridged Pyridinophane 28

Synthesis of Butadiyne-Bridged Pyridinophane 29 Route 1 Route 2

Summary The molecular network of macrocycles would serve as an appropriate template layer for guest adsorption A purpose of my work is to synthesize butadiyne-bridged pyridinophane which possesses a larger cavity and evaluate its guest inclusion. 30