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The Little Blue Box comes of Age

A review article entitled “The Story of the Little Blue Box: A Tribute to Siegfried Hünig” has been published in Angewandte Chemie International Edition by postdoctoral fellow Aspen X.-Y. Chen and former group member Hongliang Chen (now Professor at Zhejiang University).

Cyclobis(paraquat-p-phenylene), also known as the little blue box, constitutes a cornerstone of research in the Stoddart group and has facilitated the discovery of many host-gust complexes and numerous mechanically interlocked molecules during the past 35 years. Its versatility in binding small π-donors in its tetracationic state, as well as its forming trisradical tricationic complexes with viologen radical cations in its doubly reduced, bisradical dicationic state, renders it valuable for the construction of various stimuli-responsive materials and artificial molecular machines. Since it was first reported in 1988, the little blue box has been featured in over 500 publications in the chemical literature, not to mention the hundreds of solid-state structures and superstructures that have been deposited in the CCDC database. All these expansive research efforts would not have been possible without the seminal investigations carried out by Siegfried Hünig, who, not only pioneered the syntheses of viologen-containing cyclophanes, but also revealed the rich redox chemistry associated with bipyridinium-containing compounds.

While we, as well as others, have come a long way in utilizing the little blue box in a wide variety of fields in chemistry and materials science, there has, to the best of our knowledge, never been a dedicated review article to cover its rich history and its intimate connection to Hünig’s chemistry. In light of Hünig’s immense contributions to science, as well as in celebration of his almost reaching his 100th birthday, this review describes how Professor Hünig’s pioneering research led to the making of the little blue box, and how this redox-active host evolved into a key component in many mechanically interlocked molecules and artificial molecular machines.

Congratulations Aspen and Hongliang! A terrific job!

Pictured below — Aspen and Hongliang alongside the Cover Art from their review in Angewandte Chemie International Edition: