Semiconducting Diblock Copolymers

1. Semiconducting Diblock Copolymers Chemistry 765 Peter Dorff

2. Diblock Copolymers • Commercial applications: thermoplastics • Polymers as Semiconductors?

3. Why Semiconducting polymers? • Combines properties of metals into polymers •  flexibility & processing • Range of conductivities • Electroluminescence: LEDs • Very important! = $$$$$$

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

5. 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

6. Photovoltaic Cell • Inexpensive renewable energy resource • Benefit of Polymer PV cells: • Low cost fabrication, durable & flexible • Reaction:

7. Poly(p-phenylenevinylene) • Excellent charge transfer, however: • Discontinuous •  ionization potential • Photoexcitable at  450 nm • Present use in LEDs Skotheim, T.A, Handbook of Conducting polymers (New York and Basel, New York, 1986)

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

9. Luminescent Studies • PPV’s photoluminescent properties disappear •  charge transfer!

10. 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 • >5.5% energy conversion Yu, G. , Gao, J., Hummelen, J, Wudl, A, Heeger, J; Science, 270, (1995) 1789

11. A New Approach • Stalmach, U et al. & their goal • structured morphology • microphase separation of blocks • self-assembled monolayers • poly(PPV)-block-poly(___-C60) Stalmach, U et al. J. Am. Chem Soc., 2000, 122, 5464 Stupp, S. et al., Science, 1997, 276, 384

12. Objective

13. Synthesis Step 1: Polymerization of PPV • Monodispersed MW • End Functional Group

14. Synthesis Step 2: Preparation of TEMPO linker

15. Synthesis Step 3: Attachment of TEMPO • Facilitates diblock formation between very different groups

16. Synthesis Step 4. Synthesis of a Diblock copolymer • NMRP leads to monodispersed block • Random styrene / CMS block (1:1 ratio)

17. Synthesis Step 5. Functionalize with C60

18. 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