Guest Inclusion of Butadiyne-Bridged Macrocycles

Tobe Lab. M1Hiroshi Takeda

Contents

・What is Macrocycles

・ Complexation of cyclothiophene with 　　 fullerene on a surface

・My work

・ Summary

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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

3clarithromycin

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

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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 ChemistryHosts and guests held together in solution in definable structural relationshipsby 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

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Complexation of Butadiyne-Bridged Pyridinophane with Ｔ ropylium Cation in Ｓ olution

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R=C8H17

R=C8H17

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 1H-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

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R=C8H17R=C8H17

On the basis of 1H-NMR titration measurements,The nonlinear least-squares regression analysis gave K11(1:1) and K21(2:1) → For 1, K11 = 3×103 M-1 and K21 = 3×104 M-1 For 2, K11 = 1×102 M-1 and K21 = 4×102 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)

1 3 ×103 3 ×104

2 1 ×102 4 ×102

K is complex formation constant : 錯形成定数

1 2

Self-Assembly of Butadiyne-Bridged Pyridinophane

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Scanning Tunneling Microscopy (STM)

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Tunneling current

electron

Tunneling current

Tip

Sample

Tip

Sample

Guest Inclusion Ability of Butadiyne-Bridged Pyridinophane on Solid Surfaces

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The brighter spots within the cavity of 1 are trapped tropylium cations.

An empty macrocycle 1

＋

R = COOC8H171

Introduction of Paper

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cyclo[12]thiophene fullerene

Bu

≡

〜

Previous work of Monolayer of C[12]T

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Previous work of Monolayer of C[12]T

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・ 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

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・ 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

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Top view

Side view

“spider-like” comformation

About Thiophene

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Cyclic π-conjugated cyclothiophene self-assemblesat 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-C60

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・ An isolated C60 molecule (white arrow) adsorbed at the liquid/monolayer interface. ・ The electron-accepting C60 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-C60

・ Four individual C60 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.

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Complexation of C[12]T-C60

• 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-C60

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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

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・ The electron density of macrocycle’s HOMO is drastically shifted by the complexation of C60.

・ It becomes unfavorable when C60 occupy the electron-deficient part of the C[12]T macrocycle.

The macrocycle can form complex with fullerenes.

Scanning tunneling Spectroscopy (STS)

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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

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The asymmetric I–V curve was observed.

The asymmetry is clearly seenin 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–C60 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–C60 complex

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The shape of the I–V curve at positive bias is very similar to the non-complexed macrocycle. Howeverat 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) The shift of the HOMO to higher voltages (–0.9 V)

C[12]T C[12]T–C60 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–C60 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

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・ Formation of 2D molecular networks on the solid surface.

・ Guest inclusion ability toward larger guest molecule

O

O

N

OFeCl4

-

O

O OPF6

・ Synthesis of butadiyne-bridged pyridinophane which possesses a larger cavity

・ Evaluation of its guest inclusion ability

guest

host

-My purpose-

Purpose of My Work

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・ Synthesis of butadiyne-bridged pyridinophane which possesses a larger cavity

・ Evaluation of its guest inclusion in solution and on surface.

<STM image & model of macrocycle>

Synthesis of Butadiyne-Bridged Pyridinophane

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Synthesis of Butadiyne-Bridged Pyridinophane

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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.

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