Fullerenes: past, present and future, celebrating the 30th anniversary of Buckminster Fullerene

The discovery of C₆₀ and the subsequent evolution of fullerene physics and chemistry can be seen as the culmination of a series of parallel research strands pursued by Harry Kroto through numerous collaborations with colleagues and co-workers. His early career in microwave spectroscopy was informed by both the elegance of mathematics and symmetry to explain rotational selection rules [1] and the technique's ability to reveal the detailed structures of transient species. An example of the latter is work undertaken by Harry in conjunction with John Nixon on species containing atoms with multiple bonds to carbon [2]: examples include CH₂=PH and CH₃CH=S. Further developments in this line of research came through a collaboration with David Walton, who had been synthesizing molecules containing long chains of carbon atoms. Initially, these molecules, e.g. HC₅N, were seen as a means of formulating ideas concerning the coupling of rotational and bending motion; a problem not unrelated to Harry's graduate work on the quasi-linear molecule carbon suboxide, OCCCO. However, Harry was also fascinated by the chemistry of the interstellar medium (ISM), something that possibly originated from his earlier interest in laboratory experiments on the structure of C₃, a quasi-linear molecule that had been detected in comets [3].

A further link with the ISM came from the fact that HC₃N had also been detected in space [4] and Harry questioned whether or not it might be possible to observe some of the longer carbon chain molecules that he and David Walton were making and investigating in the laboratory [5,6]. A subsequent collaboration with Takeshi Oka resulted in HC₅N, HC₇N and HC₉N becoming some of the heaviest molecules identified in space [7]. It soon became apparent to Harry that large carbon-containing species could be an integral part of the composition of some interstellar dust clouds; however, it was also apparent that their presence could not be accounted for using existing ion-molecule reaction theories [8,9]. What was required was a more versatile laboratory source of carbon-containing species that might help to identify the origins of carbon chains in the ISM.

A visit by Robert Curl to the University of Sussex, UK, in the early 1980s introduced Harry to laser vaporization; a technique that Rick Smalley had been using to create transient species from refractory materials. These species are then entrained in a molecular beam, from which their spectra can be studied; studies on SiC₂ are an elegant example of the power of this technique to yield rotationally resolved spectra [10]. During visits to Smalley's laboratory at Rice University, Houston, TX, USA, in 1984–1985, two thoughts occurred to Harry. The first being that the carbon plasma formed during the laser vaporization of a graphite sample might simulate conditions found close to cool giant carbon stars, such as IRC+10216. The observation of carbon chains in the laboratory might then point to a stellar source of long chain molecules, such as those listed above. The second thought was that these carbon chains might support an earlier proposal by Alec Douglas that carbon chains could be carriers of the diffuse interstellar bands [11]—an unexplained series of interstellar spectral observations. The vaporization experiments did indeed yield evidence of carbon chains, thus supporting the idea that their interstellar presence might originate from carbon stars; however, the mass spectra of the vapour also revealed the presence of much larger carbon species, of which ions attributed to C₆₀ and C₇₀ were the most prominent [12].

Kroto et al. were not the first to observe these ions. A paper published in 1984 by Rohlfing et al. [13] gave a mass spectrum that included C₆₀ and C₇₀, although with less pronounced intensities. Where Kroto, Smalley, Curl and co-workers were able to advance the science was by first demonstrating that C₆₀ is particularly stable and then attributing that stability to the formation of a truncated icosahedral structure comprising 20 regular hexagonal faces and 12 regular pentagonal faces. They named the molecule buckminster fullerene as the proposed structure was inspired by geodesic domes of the architect Buckminster Fuller [12]; C₇₀ and other subsequently discovered allotropes of carbon with cage- or tube-like structures are known as the fullerenes.

At first, the suggestion that what were just two peaks in a mass spectrum represented a whole new branch of chemistry was met with scepticism by Harry's colleagues at Sussex and scientists elsewhere. For the next 4 years, Harry defended the significance of the discovery of C₆₀, but in the summer of 1990 his feelings were mixed when he received a manuscript by Wolfgang Krätschmer and his co-workers [14]. The work reported the isolation of C₆₀, thus vindicating the original claim of Kroto, Smalley and Curl. However, Harry and his student Jonathan Hare were just days away from isolating their own sample of C₆₀! Subsequently, fullerene chemistry developed very rapidly with the realization that—as manifest by the science reported in the contributed papers of this theme issue—fullerenes and their derivatives are a fascinating class of compounds and possess some unique and special chemical and physical properties. The nature and significance of the science described and discussed in these articles provides a clear testimony to the significant impact of the research accomplished by Harry and the considerable influence generated by his scientific vision and enthusiasm.

This theme issue originates from the 2-day symposium held on 15–16 July 2015, organized by the Royal Society of Chemistry (RSC) and the Royal Society, entitled ‘Fullerenes: past, present and future, celebrating the 30th anniversary of Buckminster Fullerene’ (figure 1). This meeting was instigated by Prof. Tony Cheetham of the Royal Society and organized by Dr Alejandra Palermo of the RSC. The majority of the reviews and reports of original research were provided by scientists who gave presentations at the July 2015 meeting and the other contributions were produced by friends and co-workers of Harry.

Figure 1.

Sir Harry Kroto, accompanied by his wife, Margaret, and participants, at the ‘Fullerenes: past, present and future,celebrating the 30th anniversary of Buckminster Fullerene’ meeting, Burlington House, UK, 16 July 2015. © Royal Society of Chemistry/MPP Image Creation.

Although weakened by the motor neuron disease with which he was diagnosed in 2014, Harry was hale and hearty throughout the meeting. Thus, he contributed with his accustomed excitement and enthusiasm to the many discussions that arose during the meeting, including an extended session overviewing the impact of the area he had effectively founded. A tribute to Harry that includes a video of an interview with him ‘In his own words’ and further information regarding the July 2015 meeting can be found at http://www.rsc.org/chemistryworld/2016/05/harry-kroto-tribute-obituary.

During the planning of this theme issue, Harry agreed to write a preface; however, circumstances prevented this. Dave Garner has instead written a dedication to Harry, a fellow past President of the RSC. He and we, as the Editors of this theme issue, would like to formally thank all of those involved in the organization of the July 2015 meeting, the contributors to this issue, Bailey Fallon—the Commissioning Editor of Philosophical Transactions of the Royal Society A—and members of the editorial office of the Royal Society who have helped to make this memorial issue possible.

Harry is greatly missed by all of us who knew him, especially for his kindness and enthusiasm. His tenacious advocacy for science and education of the young had global impact and many, many thousands of children and educators were addressed in an activity with global impact. Harry is remembered with affection by all who knew him; this collection of science stems from the discovery of C₆₀ and is a small thank you on behalf of a very large community.