Semiconducting Diblock Copolymers

Chemistry 765

Peter Dorff

Diblock Copolymers

• Commercial applications: thermoplastics

• Polymers as Semiconductors?

n n n n n n

Why Semiconducting polymers?

• Combines properties of metals into polymers flexibility & processing

• Range of conductivities

• Electroluminescence: LEDs

• Very important! = $$$$$$

Semiconducting Polymers• Initial work in 1968 by Dall’Olio et al.2

• synthesis of polypyrrole on Pt electrode

• electrical conductivities of = 8 Ω-1 cm-1

• Diaz, A et al. in 1979 synthesized • stable, manageable polymeric films• electrical conductivities of = 100 Ω-1 cm-1

HN

n

HN

n

+

+ e-

Skotheim, T.A, Handbook of Conducting polymers (New York and Basel, New York, 1986)

Doping of Polymer

• Popular Method

• developed in 1970s

• “doping”with e- donor & acceptor

• permits charge transfer• iodine polyacetylenes ( = 360 Ω-1 cm-1)

(CH)x + D+ + A- (CH)x+A- + D

(CH)x + D+ + A- D+(CH)-x + A

Photovoltaic Cell

• Inexpensive renewable energy resource

• Benefit of Polymer PV cells:

• Low cost fabrication, durable & flexible

• Reaction:

D + A 1,3D* + A

Step 1, Excitation on D: Step 3, charge transfer initiated:

1,3(D-A)* 1,3(D+-A-)*

Step 5, charge separation:

1,3(D+.-A-.) D+. + A-.

Poly(p-phenylenevinylene)

• Excellent charge transfer, however:• Discontinuous ionization potential

• Photoexcitable at 450 nm• Present use in LEDs

OR

RO

OR

RO

OR

RO

OR

RO

Skotheim, T.A, Handbook of Conducting polymers (New York and Basel, New York, 1986)

Evolution of Polymer PV cells

• Research by Sariciftci, N.S et al. in 1992

• Dope PPV with C60 & spin cast into film

• C60 accepts 6 e-

OR

RO

OR

RO

OR

RO

OR

RO

n

C60

e-e-

Sariciftci, N. S et al. ibid. 62, 585 (1992)

Luminescent Studies

•PPV’s photoluminescent properties disappear charge transfer!

Progression

• Research by Yu, G et al in 1995:

• 1/3 energy lost via luminescence

• Charge transfer occurs at D-A interface Soluble C60 derivatives

OCH3

O [5,6]-PCBM

• >5.5% energy conversion

Yu, G. , Gao, J., Hummelen, J, Wudl, A, Heeger, J; Science, 270, (1995) 1789

A New Approach

• Stalmach, U et al. & their goal

• structured morphology» microphase separation of blocks» self-assembled monolayers

• poly(PPV)-block-poly(___-C60)

Coil (PS-CMS)

Rod (PPV)

Stalmach, U et al. J. Am. Chem Soc., 2000, 122, 5464

Stupp, S. et al., Science, 1997, 276, 384

Objective

OR

RO

OR

RO

OR

RO

OR

RO

Rod = PPV

Coil = PS-C60

Synthesis

Step 1: Polymerization of PPV

OR

CHO

OR

CH3

OR

OR

CH3

OR

CHO

OR

n

R=C8H17

1) Aniline2) KOtBu, DMF

• Monodispersed MW

• End Functional Group

Synthesis

Step 2: Preparation of TEMPO linker

NO

Br

O N

MgBr

O N1) Br22) Styrene Mg

Synthesis

Step 3: Attachment of TEMPO

OR

OR

CH3

OR

CHO

OR

OR

OR

CH3

OR

CH

OR

OH

CH2HC NO

nMgBr

O N

n

• Facilitates diblock formation between very different groups

Synthesis

OR

OR

CH3

OR

CH

OR

OHCH2

HC NO

OR

OR

CH3

OR

CH

OR

OH

CH2Cl

NO

(n) Styrene(m) 4-chloromethylstyrene

n

n

n m p

Step 4. Synthesis of a Diblock copolymer

• NMRP leads to monodispersed block

•Random styrene / CMS block (1:1 ratio)

Synthesis

Step 5. Functionalize with C60OR

OR

CH3

OR

CH

OR

OH

CH2Cl

NO

OR

OR

CH3

OR

CH

OR

OH NO

n

n m p

n

n m p

C60, CuBr, Cu, bipy

CH2Cl

110 oCCu(I), bipy

Cu (II) Cl bipy

CH2

ATRP

Conclusions

• Successful synthesis of rod-coil block copolymers

• Self-assembly into honeycomb monolayers

• Quenching of luminescence with excitation

• Future work in applying polymer to prototype photovoltaic cell