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The bandgap (Eg) of conjugated materials effects a variety of critical properties such that efforts to control the bandgap have become a basic tenet in the design of conjugated polymers. One goal of such efforts is to minimize the Eg with the goal of producing technologically useful low bandgap (Eg < 1.5 eV) polymers. This perspective will introduce the two primary approaches to low Eg polymers (i.e., quinoidal systems and donor-acceptor frameworks) and discuss important new directions for both design principles. 

Polyaniline, one of the primary parent conducting polymers, is a quite old material with a history dating back to 1834. With the distinction of being the oldest known fully synthetic polymer and successfully commercialized as several popular cotton dyes in the 1860s, this material was originally known by the name of its black dye, aniline black. Of course, throughout this early history, the chemical identity and structure of these early polyaniline products were completely unknown, and it was not until the 1870s that initial attempts began to reveal various structural aspects. The current report will present a detailed historical account of the efforts to determine the structures of these early aniline oxidation products over the time period of ca. 1870-1915. In addition to the identity and structure of specific products, studies revealing the interconversion of one species to another via both redox and acid-based processes will also be discussed, with these collective efforts resulting in a comprehensive model of these materials that has remained essentially unchanged to this day. 

A series of model oligomers consisting of combinations of a traditional strong donor unit (3,4-ethylenedioxythiophene), a traditional strong acceptor unit (benzo[ c ][1,2,5]thiadiazole), and the ambipolar unit thieno[3,4- b ]pyrazine were synthesized via cross-coupling methods. The prepared oligomers include all six possible dimeric combinations in order to characterize the extent and nature of donor–acceptor effects commonly used in the design of conjugated materials, with particular focus on understanding how the inclusion of ambipolar units influences donor–acceptor frameworks. The full oligomeric series was thoroughly investigated via photophysical and electrochemical studies, in parallel with density functional theory (DFT) calculations, in order to correlate the nature and extent of donor–acceptor effects on both frontier orbital energies and the desired narrowing of the HOMO–LUMO energy gap. The corresponding relationships revealed should then provide a deeper understanding of donor–acceptor interactions and their application to conjugated materials. 

Advances in the synthesis of low bandgap (Eg < 1.5 eV) conjugated polymers has produced organic materials capable of absorbing near-infrared (NIR) light (800—2500 nm), with these materials first applied to photodiode NIR detectors in 2007 as an alternative to more traditional inorganic devices. Although the development of organic NIR photodetectors has continued to advance, their ability to effectively detect wavelengths in the low-energy portion of the NIR spectrum is still limited. Efforts to date concerning the production of photodiode-based devices capable of detecting light beyond 1000 nm are reviewed. 

In 2000, the Nobel Prize in Chemistry was awarded to Hideki Shirakawa, Alan G. MacDiarmid, and Alan J. Heeger “for the discovery and development of electrically conductive polymers.” While this award was in reference to their collaborative efforts on conducting polyacetylene in the mid-to-late 1970s, the narrative leading up to these efforts began in 1967 with the production of polyacetylene plastic films via what has been called a “fortuitous error.” At the heart of this discovery were Shirakawa and a visiting Korean scientist, Hyung Chick Pyun. The current report provides background on Pyun and, for the first time, presents his version of the events leading to the discovery of polyacetylene films in order to provide new insight into this important historical event.