A Polymer Lost in the Shuffle: The Perspective of Poly(para)phenylenes

Abstract

During 1990s, poly(para)phenylenes (PPPs) are one of the most prominent and hyped classes of conjugated polymers. Even though they have been heavily investigated for different applications, they are now eking out a rather niche existence. It is believed that this decline of interest partly has come from the early obstacle of synthesizing high-molecular weight, processable, and defect-free PPPs. Early examples of PPPs are not only rather oligomers than polymers but also contain many regiochemical and structural defects. Furthermore, early unsubstituted materials are infusible and insoluble, which have made their practical application almost impossible. Another reason for the decline of research interest in PPPs may be their underperformance in early applications, particularly in organic light-emitting diodes (OLEDs), which ultimately lead to a lack of follow-up publications. However, over the last two decades not only more precise and advanced synthesis methods have arisen but also a more profound understanding of those applications has been achieved within which new technological approaches have emerged. It is believed that PPPs would benefit from this development. Accordingly, in this perspective, the synthesis, structures, properties, and applications of PPPs reported so far as well as their potential in future technologies are discussed.