2011. 06. 29.

Tobe Laboratory

Kitabayashi Kenichi

1

Synthesis and Physical Properties of Zethrene Derivatives

with Singlet Diradical Character

Contents1. Introduction - singlet diradical - two-photon absorption

2. Background - singlet diradicals synthesized so far

3. Zethrene - singlet diradical character of zethrene - previous research in our group

4. My project

5. Summary

2

y = 1y = 0

closed shell singlet diradical

0 < y < 1

open shell

ethylene cyclopentane-1,3-diyl

diradical character

y

Singlet Diradical

H H H H H H

H

HH

H

p-quinodimethane 3

Singlet diradicals are compounds having characteristic electron structure, that is, two electrons on the radical centers are weakly coupled.

閉殻 開殻一重項ジラジカル

Singlet open-shell molecule with intermediate diradical exhibits enhanced g value.

Spatially-selective excitation

Two-Photon Absorption

hn hn’

4

singlet ground state

first excitedsinglet state

second excitedsinglet state

hn’

H H H H H H

Nakano, M. et al. Phys. Rev. A 1997, 55, 1503.

gS1

uS1

gS2

two-photon absorption g: second hyperpolarizabilities 第二超分極率

Singlet Diradicals Synthesized So Far

1.448 Å

1.420 Å1.372 Å

1.429 Å

Montgomery, L. K. et al. J. Am. Chem. Soc. 1986, 108, 6004.

1.381 Å

1.449 Å 1.346 Å

1.415 Å

Chichibabin‘shydrocarbon

Thiele‘shydrocarbon

Ph

Ph Ph

Ph

Ph

Ph Ph

Ph

p-quinodimethane poly-p-xylylene

unstable

5

Ph

Ph Ph

Ph

Ph

PhPh

Ph

Ph

Ph Ph

Ph

Ph

PhPh

Ph

H2C CH2n

Ph =

y = 0.76

Kubo, T. et al. Angew. Chem. Int. Ed. 2005, 44, 6564.

6

Singlet Diradicals Synthesized So Far

y = 0.81

Kubo, T. et al.J. Am. Chem. Soc.2010, 132, 11021.

Ph

Ph

Ph

Ph

etc.

t-Bu

t-Bu

t-Bu

t-Bu

t-Bu

t-Bu

t-Bu

t-Bu

Mes

MesMes

Mes

Mes =

crystal structure

3.137Å

top view

side view

t-Bu = C CH3

CH3

CH3

714

7

Singlet Diradical Character of Zethrene

Nakano, M. et al. Comp. Lett. 2007, 3, 333.

Zethrene is predicted to exhibit moderate singlet diradical character (y = 0.41) by computational studies.

zethrene(dibenzo[de,mn]tetracene)

7147 714

14

spin density

It is predicted theoretically that large spin density and frontier orbital coefficients of zethrene are located at the 7,14-positions.

LUMO −2.34 eVHOMO −4.56 eV (B3LYP/6-31G*)

Tobe, Y. et al. Pure Appl. Chem. 2010, 82, 871.

8

NC

CN

HOOC

COOH

ClOC

COCl

O

O

O

O

COOH

HOOC

O

O

O

O

(EtO2C)2HCOC

COCH(CO2Et)2

Pd-C- CO2

12% < 8%94%87%

H2SO4 HI

1) 20% KOH2) HCl SOCl2 CH2(CO2Et)2

Mg

78%

zethrene

Stepwise Synthesis of Zethrene by Clar

Clar, E. et al. Chem. Ber. 1955, 88, 1520.

Low accessibility and high sensitivity to air and light.

Physical properties of zethrene are almost unknown.

I I

II II 714

R

R R

R R

R

R

R R

R R

R

PhPd, Cu

R

R R

R

Ph

Ph

68% 88%

1a : R = H1b : R = t-Bu

2a : R = H2b : R = t-Bu

3a : R = H3b : R = t-Bu

9

Previous ResearchSynthesis and Physical Properties of Bis(phenylethynyl)zethrene

250 350 450 550 650 7500

10000

20000

30000

40000

50000

wavelength / nm

e / m

o l L

-1 c

m-1

-2.5 -2 -1.5 -1 -0.5 0 0.5 1 1.5voltage / V

transannular cyclization

crosscoupling

UVlmax / nm (e / mol L-1 cm-1)

FLlmax / nm (F) Ered2 / V Ered1 / V Eox1 / V Eox2 / V

578 (22400) 　541 (17200) 619 (0.05) – -1.85 +0.12 +0.61

Tobe, Y. et al. Org. Lett. 2009, 11, 4104.

3b

UV / vis

FL CV

zethrene

TPAcross−section

diphenylzethrene

492 GM(650 nm)

509 GM (604 nm)

1138 GM (604 nm)

zethrene

diphenylzethrene rubrene

67 GM (612 nm)

rubrene

0.4320.407 0.324diradical character ̶O

GM = 10−50 cm4 s photon−1 molecule−1

10

Previous ResearchTPA Cross-Section of Zethrene Derivatives

3bWu, Y. T. et al. Angew. Chem. Int. Ed. 2010, 49, 7059.

bis(phenylethnyl)zethrene

PhPhPh

t-Bu t-Bu

t-But-Bu

Ph

3b

TPA cross−section : 二光子吸収断面積

My ProjectZethrenedimer (Candidate for Tetraradical)

Bertrand, G. et al. Angew. Chem. Int. Ed. 2004, 43, 4876.

Interaction between diradicals

11

Ph

Ph

Ph

Ph

4 5

Ph

Pht-But-Bu

t-Bu t-Bu

t-But-Bu

t-But-Bu

Ph

Pht-But-Bu

t-Bu t-Bu

t-But-Bu

t-But-Bu

C

Ph

CPh

t-But-Bu

t-Bu t-Bu

t-But-Bu

t-But-Bu

tert-butyl groups are substituted to hydrogen for clarity.

t-BuBP

PBt-Bu

i-Pr i-Pr

i-Pr i-Pr

BBP

PB

PB

Pt-But-Bu

i-Pr i-Pr

i-Pr i-Pr i-Pr i-Pr

i-Pr i-Pr

BBP

PB

PB

Pt-But-Bu

i-Pr i-Pr

i-Pr i-Pr i-Pr i-Pr

i-Pr i-Pr

PhPd(PPh3)4, CuI

Et3N

Ph

Br

7

Pd(PPh3)4, CuI

Et3N

TMSPh

8

TMS

K2CO3Ph

9

THF, MeOH

Ph

4

Ph

Pd(0), Cu(I)7

IBr

CHCl3Br

6

Br

1b

t-Bu

t-Bu t-Bu

t-Bu t-Bu

t-Bu t-Bu

t-Bu t-Bu

t-Bu t-Bu

t-Bu t-Bu

t-Bu t-Bu

t-Bu

t-Bu

t-Bu t-Bu

t-But-Bu

t-Bu t-Bu

t-Bu

t-Bu

t-Bu t-Bu

t-Bu

12

My ProjectSynthetic Plan for Zethrenedimer 4

TMS = Si CH3

CH3

CH3

In progress

13

Summary

• Recently, p conjugated compounds with a large diradical character have been studied experimentally and theoretically.

• Our group developed convenient synthetic method of stable zethrene derivatives

• TPA cross-section of 3b is much larger than that of rubrene most probably due to the diradical character of 3b.

• Synthesis of zethrenedimer 4 including two diradicals is in progress.