This work is devoted to the rational design of conjugated polymers for optoelectronic applications. I have synthesized and studied structure-property relationships in cationic polymers for electrochromic applications and “ladder” polymers for organic light emitting transistors. Cationic conjugated polymers are widely used as sensors, electrochromic materials and interfacial layers. However, most of them rely on charged side chains. To satisfy the unmet need in new classes of conjugated polymers with positive charges incorporated into the π-system, we designed a new positively charged monomer with a fused pyridine ring. Based on this motif, we have synthesized a series of conjugated cationic polymers by Stille polycondensation. Through iterative design and side-chain engineering we improved solubility and electrochemical stability of these materials and found that they exhibit red-green electrochromism. Counterion optimization decreases switching time and opens new opportunities for design of electrochromic materials. Organic light emitting transistors combine light emission and transistor control in one device. OLET materials must exhibit efficient luminescence, high ambipolar mobility and excellent processability. However, these properties are at odds with each other – π-π stacking benefits charge transport, but decreases luminescence. To solve this issue we designed and synthesized a series of “twisted” conjugated polymers that can be continuously cyclized by oxidation to provide “ladder” type polymers with fused rings in the main chain. Using this approach we found a partially cyclized polymer that is best for light emission due to balance between charge transport and quenching of luminescence in solid state. Oxidative cyclization allows to gradually tune optical and electronic properties of synthesized materials for improved OLET performance.