◾ Thiophene-Based Conjugated Polymers: Synthesis, Linear, and Third-Order Nonlinear Optical Properties
Extensive research work in the field of CPs has started in late 1970s with the discovery of electrical conductivity in oxidatively doped poly(acetylene) . This important discovery led to the award of Nobel Prize in chemistry in the year 2000 to three scientists: Hideki Shirakawa, Alan G MacDiarmid, and Alan J. Heeger. This pioneering work motivated the researchers to synthesize and to study the properties of other new classes of π-CPs based on aromatic precursors such as p-phenylenevinylene, thiophene, pyrrole, carbazole, fluorene, and their derivatives (Figure 16.2) [2-5]. Early work in this field held the hope that these types of polymer systems would serve as replacements for highly conductive metals, such as copper and aluminum for electrical transport or related applications. However, due to the instability of these systems when highly doped, other more practical uses have been realized such as polymer light-emitting diodes (PLEDs) [6-11]. Moreover, in order to tune the specific properties desired for end-user applications, a proper modification of the monomer structure is essential that manipulates both the electronic and optical properties of these polymer systems.