This doctoral thesis focuses on the design and synthesis of novel organic semiconducting materials. Theoretical part addresses the importance of how the molecular structure modifications could affect the overall performance in a final device. The experimental part follows up and presents novel imine and chalcone derivatives of para-bis(2-thienyl)phenylene, polythiophenes with adamantylalkyl side-chain, and finally copolymers for ion-sensing applications. Detailed study of the properties important for the organic electronics is described in the results and discussion section, focusing mainly on the optoelectronic characteristics and molecular orientation. Possible applications of the newly synthesized materials are also outlined together with the planned future research focus.