semiconducting diblock copolymers
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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
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