Electron Donor-Acceptor Organic Polymers by “Click” Type Cycloaddition/Retroelectrocyclization Reaction

The “click” type cycloaddition/retroelectrocyclization reaction is an intriguing approach for synthesizing electron donor-acceptor organic polymers. This chapter covers the fundamental reaction mechanism and the basic principles of applying this reaction to the synthesis of organic polymers via postfunctionalization or step-growth polymerization. The electron donor-acceptor moieties can be incorporated into the main-chain and/or side-chain of both conjugated and nonconjugated polymers. These polymers feature attractive properties including intramolecular charge-transfer bands, nonlinear optical properties, redox activities, third-order nonlinear optical properties, and enhanced thermal stability. Because of this, these polymers have found a variety of applications such as colorimetric chemosensors of metal ions, nonlinear optics, and solar cells. This novel “click” chemistry paves a unique path toward the synthesis of next-generation functional materials that cannot be accomplished by the incumbent synthetic methods. Atom transfer radical polymerization (ATRP) of N,N-didodecyl-4-[(4-vinylphenyl)ethynyl]aniline was conducted with bromine-terminated polystyrene to synthesize block copolymers composed of unsubstituted polystyrene and electron-rich alkyne functionalized polystyrene segments. These block copolymers were then reacted with TCNE to introduce electron donor-acceptor chromophores into the side chains of polymers to produce TCNE-adducted polymers ( P29 ). P29 exhibited intense charge-transfer bands, well-defined redox activities, and good thermal stability. In addition, polymer thin films based on P29 were prepared by spin coating on a glass slide. The second harmonic genera-tion (SHG) of these thin films was measured before and after electric poling. The results showed that the SHG coefficient (d 33 ) of the poled thin film was as high as 3.0 pm/V [70].