ABSTRACT
The story of discovery of C60 buckminsterfullerene is not only multifaceted but also convoluted, and this makes the assembly of a coherent, straightforward account very difficult, if not impossible. The bare bones are to be found in three key papers: (a) An experiment, in 1985, designed to re-create the conditions in cool carbon stars serendipitously uncovered the existence an all-carbon species which was conjectured to be a molecule consisting of 60 equivalent C atoms located at the corners of a truncated icosahedral closed cage [1a]. (b) In 1990 the molecule was extracted by sublimation from the deposit of a carbon arc and the spheroidal shape proven by X-ray analysis [2]. (c) Simultaneously, in 1990,
Keywords: fullerenes, self-assembly, nanotechnology, C60, carbon, micro-wave spectroscopy, photodissociation, mass spectrometry, Buckyball, Buckminsterfullerene, icosahedral, arc-discharged carbon, carbon soot, Isolated Pentagon Rule (IPR), Isolated Multiplet Pentagon Rule (IMPR), diffuse interstellar bands (DIBs)
the molecule was created independently, solvent-extracted and the truncated icosahedral pattern confirmed by the detection of a single NMR line and the chromatographic method of isolating fullerenes developed [3]. Furthermore in this study the ultimate unequivocal confirmation that a whole family of fullerenes existed was obtained by the detection of the 5-line NMR spectrum for C70. Then the field exploded and today, on average, about a thousand papers are published each year describing research advances involving fullerenes. An essentially complete review [4] surveyed the status of the fullerene field up to December 31, 1990. It is arguable, and I would argue it, that the main aspect of the discovery was not the fact that C60 could be created, but that it self-assembled spontaneously, because this resulted in a reassessment of our perspective on the general dynamic factors which control structure assembly processes at nanoscale dimensions. In so doing it kick-started nanoscience and nanotechnology and became an iconic character of the field.By themselves the published research papers present a rather arid account, yielding little insight into how and why the breakthrough actually occurred. This is almost always the case in science where personal accounts are rarely available. However, in this case many were genuinely interested in the breakthrough and several personal accounts, and general articles were written by some members of the groups primarily involved in the discovery and extraction [5-16] Numerous articles were published by journalists such as that by Taubes [17] in general science magazines as well as two books [18, 19] and a collection of rather intimate interviews by Hargittai [20].The origins of the name “buckminsterfullerene” and the family name “fullerene” are discussed by Applewhite [21] and Nickon and Silversmith [22]. There was also a film produced by the BBC, some excerpts of which may occasionally be viewed on YouTube [23]. There are numerous indirect accounts often propagating inaccuracies, to be found littering the literature; for instance, several accounts claim, erroneously, that C60 was first detected in space! Having perused the plethora of material available, I still feel that many interesting aspects are missing and the recent compendium [1b] attempts to fill some of the interesting gaps and help to create a more satisfying and intimate picture of how the discovery actually came about. The articles and reprints collected in
60the compendium [1b] should be considered more as a supplement to previous accounts offering a more detailed perspective on the breakthrough and the way advances in general often arise by the confluence of ideas and factors from widely differing sources.When a convoluted event occurs, “Rashomon” factors occasionally apply in that some contributions do not appear to fit well together. The film Rashomon by director Akira Kurosawa, which is based on two short stories, “In the Grove” and “Rashomon” by Ryűnosuke Akutagawa, deals with this sort of situation. The determination of what actually happened was not Kurosawa’s aim in this film as all the accounts are completely incompatible and embellished by each individual’s personal ego. However, in a real situation something definite actually happens and the lesson I personally draw from Rashomon is that in a real case individuals tend to present their personal “realities” and these can offer deeper and more complete insights into multifaceted events. Basically Objectivity with a capital O is to be found in the Totality of the Subjectivity with capitals T and S, respectively. An interesting corollary of Kurosawa’s thesis is that individuals, not directly involved who seek to present the definitive story, can also not be relied upon to evince disinterested accounts as they present their own personal “biased” views! The conclusion is that there is no such thing as a single “objective” story containing no conflicting elements!The recent compendium [1b] contains copies of most of the papers detailing advances that I personally (!) feel were crucial steps on the way to the discovery of the fullerenes and their extraction. Because existing accounts in my opinion [5-16] paint an incomplete picture, I asked some key researchers who laid the foundations for the discovery or were involved with key aspects of the story to contribute to an introductory section of the compendium [1b]. Fortunately almost all kindly agreed to pen their recollections and their new accounts provide fascinating new insights into how the breakthrough occurred and highlight the fact that scientific research is an intrinsically human and totally unpredictable activity. With hindsight I think one can recognize at least three major trails leading inexorably to the revelation that, like Orson Welles who lurked in the shadowy backstreets of Vienna in the famous film The Third Man, a third well-defined allotropic form of carbon has, since time immemorial, been
Ta bl
e 14
.1 Diag
ramma ticrepr
esentat ionoft
hevari ousdis
parate pathwa
yswhic hledu
ptoth edisco
veryof C 60in
thelab oratory
andsp
ace 1 Ca
60lurking in the dark recesses of the universe. It is hard to credit the fact that the discovery of a molecular allotrope of carbon did not occur until nearly the end of the 20th century when the element involved is the most multitalented and by far the most well-studied in the Periodic Table. The breakthrough involved the amalgamation of a kaleidoscope of disparate research studies and the diagram in Table 14.1 has been devised to provide a semblance of rational order. Discoveries that appear to arrive from “left field” litter the sciences and serve as a ubiquitously unheeded warning to those who think they know how science should be done and what science should be funded. 14.1 Carbon Cluster StudiesThe Carbon Cluster Pathway involved the development of techniques to study the mass spectra of molecules and clusters of refractory materials, in particular carbon. Between 1958 and 1963 Hintenberger and colleagues published a series of fascinating papers which contain what I consider to be landmark mass spectrometric observations on pure carbon species which they found in the products of arc-discharged graphite [24]. They observed species with as many 33 carbon atoms! It is interesting to conjecture how different the history of the fullerenes might have been had their study extended to twice as many atoms! Another key event was the development of the supersonic nozzle by Roger Campargue which produced cold ensembles of molecules in the gas phase [25]. A review article outlining his personal perspective is reproduced here [26]. The next step on this trail was the combination of the supersonic nozzle with a tunable laser in a landmark advance by Rick Smalley, Lennard Wharton and Donald Levy which enabled them to produce molecules in the gas phase at sufficiently low internal temperatures which facilitated the analysis of extremely complex electronic spectra, such as that of NO2 [27]. Lennard Wharton has written an account of his personal recollections [1b], which reveals just how much careful background work was involved in developing this major breakthrough. During the research on this introductory chapter, quite fortuitously, Sydney Leach, a long-time friend and occasional coworker, mentioned his involvement with the start of Roger’s nozzle studies
and Sydney has sent a short (already published) anecdote [1b] about the way in which Roger’s original gas phase dynamics research programme came into being. This is a further fascinating insight into the seemingly haphazard and totally unpredictable way that important scientific breakthroughs occur.The next crucial step and certainly the most technically crucial step was the creation of the laser vapourisation supersonic cluster beam instrument by Rick Smalley’s group at Rice University in 1981 [28]. This advance enabled the mass spectra of large clusters created from refractory precursor materials to be detected for the first time and in some case the measurement of their spectra, such as SiC2 [29]. This elegant technique, more than any other, has revolutionised the study of refractory clusters, and Michael Duncan, who was a PhD student on this development, has also contributed a detailed and quite fascinating personal account [1b] which shows how this major breakthrough came about. In particular Michael describes how the machine, affectionately named “Ap2” which uncovered the existence of C60, came to be constructed in the first place. It is my view that the discovery of C60 was the raison d’être of this brilliant technical advance. 14.2 Carbon Chains in Space and Stars
The Carbon Chain Pathway started in a totally different field with the development of organic synthetic techniques by David Walton at Sussex who created extended linear carbon chain structures called polyynes with alternating single and triple bonds [30-32] and the study of the molecular dynamics of these chains by molecular spectroscopy (microwave rotational spectroscopy) in a collaboration between David and my spectroscopy group. In fact the key catalyst was a unique Chemistry by Thesis course, initiated by the then dean of the School of Molecular Sciences, Colin Eaborn. In this course chemistry undergraduates at the University of Sussex were able to obtain BSc degrees by carrying out research more or less full-time for two years. The student involved in the study of the first cyanopolyyne HC5N, Anthony Alexander, did an outstanding job [33]. When the rotational frequencies had been measured they were used in a collaboration
60between our Sussex group and Takeshi Oka, Lorne Avery, Norm Broten and John Macleod at the National Research Council (NRC) in Canada, and this resulted in the discovery by radioastronomy of the unexpectedly high abundance of HC5N in the interstellar medium [34]. Then Colin Kirby, at the time a grad student, achieved the difficult synthesis of HC7N devised by David and measured its spectrum [35] which enabled us to detect it in space [36]. Then using the frequencies Takeshi imaginatively predicted the frequency of HC9N and we detected it as well [37]. It was this series of Sussex/NRC laboratory and radioastronomy studies which uncovered the, at the time amazing, abundance of the long carbon chain molecules in space. The next step in the story was the detection by Eric Becklin, Gerry Neugebauer and their coworkers of an amazing object emitting infrared radiation an order of magnitude greater than any previously observed IR source and the identification of the object as the cool red giant carbon star IRC+10216 [38].Eric has also provided a personal account in the compendium [1b] which nicely captures the euphoria that often accompanies a moment when an important discovery is made, in this case of an exceptional new source of infrared radiation. A subsequent radioastronomy study focused on this star resulted in the exciting (certainly to me) observation by Gisbert Winnewisser and Malcolm Walmsley [39] that our long carbon chain cyanopolyynes molecules were being ejected from IRC+10216 into the interstellar medium. These results catalysed preliminary conjectures about the importance of carbon in the interstellar medium and stars [40, 41] which were later to stimulate the experiments which resulted in the discovery of C60. 14.3 Carbon in Space Dust and the Diffuse
Interstellar Bands (DIBs)A third primary pathway involves a couple of “Interstellar Mysteries” which are arguably two of the most intriguing in the whole of the sciences. One involves a discovery, made originally in 1922 by Heger, of some curious absorption features in the spectra of stars [42] which came to be known as the diffuse interstellar
bands (DIBs). The interstellar nature of these features was unequivocally confirmed during the 1930s and their properties summarised by McKellar in 1940 [43]. The DIB field has been extensively and carefully reviewed by Herbig [44, 45]. The tantalising puzzle of the nature of the carrier is still today, almost a century later, unsolved, although scores of spectroscopists and astrophysicists have ruminated long and hard over the identity, observationally, experimentally and theoretically. The observing sessions which revealed the abundance of the carbon chains in space were carried out at the National Research Council Telescope in Algonquin Park Canada, and I went there a few times to participate in our observations. During one of these visits Alec Douglas discussed his thoughts with me on the carriers of the DIBs and in particular he suggested the possibility that extended carbon chain species related to those we had discovered might be involved [46]. A second important interstellar feature is also involved in the story. This is a strong absorption band at 217 nm which Stecher conjectured might be due to carbonaceous dust particles [47].Subsequently Day and Donald Huffman carried out a very important laboratory study on the UV spectrum of carbon smoke and showed that this conjecture was quite convincing [48]. 14.4 C60 Pre-discovery Experiments
The specific aim of the discovery experiment was actually very simple: To simulate the supposed chemistry in the atmosphere of a star such as IRC+10216 and show that the polyynes HCnN (n = 5, 7, 9), which we had detected in the ISM, could be created when carbon atoms nucleate in an atmosphere containing nitrogen and hydrogen (e.g. NH3) and so support my hypothesis that the chains originated in stars [40, 41]. At the time, in situ ion molecule reactions [49, 50] and/or grain surface catalysis [51] were the two strongest candidates able to account for most other interstellar molecules. In my mind neither theory could account for the chains we had observed as there appeared to be too many “heavy” carbon atoms to be created by the very slow processes in the very tenuous interstellar gas and they also were surely just too heavy to be
sufficiently easily vapourised from a solid surface. Bob Curl had invited me to visit Rice after a conference organised by Jim Boggs at Austin, and during this visit in Easter 1984 Bob showed me a manuscript detailing a resonant 2-photon ionisation (R2PI) spectrum obtained by Rick Smalley’s group which indicated that SiC2 had, unexpectedly, a triangular structure [29]. This was extremely interesting to me as my group had focused over the previous decade on the creation of whole families of new molecules involving multiple bonds to second and third row elements (i.e. containing >C = S, >C = Se, —B = S, >C = P — and — C ≡ P moieties) [41] and I had been ruminating for quite a while over how we might tackle the problem of creating molecules containing the >C = Si< moiety, which I knew would be quite difficult. Bob encouraged me to go over to see Rick in his laboratory and while Rick was describing Ap2, which was his pride and joy at the time, the basic experiment described above formed in my mind. Furthermore, the possibility of a second experiment also formed: This was to measure the R2PI spectra of various carbon chain species and confirm or otherwise the contention of Alec Douglas’s that carbon chains might be the carriers of the DIBs [46]. That evening in the Curl household, I discussed these ideas with Bob, and over the following 17 months the technical issues, mainly pertaining to the difficulties involved in carrying out the more complex R2PI/DIB experiment, were the subject of letters sent to and fro between us (these were pre-email days!).Two or three months after my Easter 1984 visit to Rice, I was sitting in the Sussex University Chemistry Laboratory coffee room when my colleague Tony Stace handed me a copy of a fascinating paper [52] by a group at Exxon which to my amazement, and “slight” irritation, presented details of essentially the basic experiment I had proposed three months previously to the Rice group. This paper contained the most fascinating new observation that the overall carbon mass spectrum pattern was actually bimodal and that in addition to the set detected by Hintenberger’s group [24], which seemed to peter out around C30 or so, a second set of only even numbered species began to appear above ca. C30 rising to a maximum in the C50 to C70 region and tailing off around C100. The Exxon group suggested these new features were due to “carbyne” [53], a mythical creature whose existence has been the
subject of controversy for getting on for half a century [54]. In 1982 Smith and Buseck had shown essentially conclusively that the “carbyne” proposal had been based on an experimental artifact [55]. One thing about which I was pretty certain was that this hypothetical material made no more sense from a chemical point of view than the Loch Ness Monster makes from an evidence-based logical viewpoint. Polyynes explode with great violence if any attempt is made to isolate and condense them, and in our Sussex microwave spectroscopy work we took great precautions to ensure they remained in the vapour phase at low pressures. After the discovery experiment in September 1985 [1a] we realised that the mass spectrometric peak of C60 in this Exxon paper was actually somewhat stronger than other adjacent peaks but the significance of this strength had gone unrecognised. A second paper by Bloomfield et al., also carried out prior to our experiment, had probed the photodissociation characteristics of C60 [56]. As far as I can tell, neither of these two groups varied the clustering conditions with a view to probing the creation process itself. Had this been done I suspect that both groups would have realized that the C60 signal could be made dominant and this would have alerted them to the fact that something exceptional was involved and worthy of further careful examination. Thus we realised that C60 had been in the literature for some 18 months prior to our discovery in September 1985. Although scores of researchers must have seen the peak (I also)—it was even labelled C60-no one appears to have considered it seriously! When I first saw the Exxon paper my first reaction was that the new family of only even-numbered carbon species might be planar graphene flakes of various shapes and sizes. That even-numbered graphene flakes might be more stable than odd-numbered ones did not seem that implausible at the time. 14.5 The Discovery of C60
In September 1985, about 17 months after my first visit, Curl and Smalley finally agreed that we should carry out the basic experiment which I had proposed. The carrot for the Rice group was that the basic experiment, to simply simulate a stellar carbon atmosphere,
60was, to all intents and purposes, a necessary preliminary to the much more complicated and seemingly “more important (!)” DIB study. The actual discovery experiments were carried out by the students Jim Heath, Sean O’Brien, Yuan Liu and me in the space of less than two weeks. A fourth student, Qing-Ling Zhang, who had only just started was also involved in some of these experiments. The students threw themselves wholeheartedly into the project, especially Jim Heath. We also had an improved weapon at our disposal, in the shape of a refined nozzle assembly, which Sean had designed. At the start of the experiments we had a rather irritating problem in that we were unable to print out our data, but fortunately Yuan worked hard to resolve this problem and within a couple of days, on 4 September 1985, we had a paper copy showing a dominant mass spectrometric peak at 720 amu which indicated that a species with 60 carbon atoms was very special indeed (Fig. 14.1).
