Fullerene Cations Research Articles

Gas-phase formation of fullerene/9-hydroxyfluorene cluster cations

ABSTRACT In interstellar environment, fullerene species readily react with large molecules (e.g. polycyclic aromatic hydrocarbons, PAHs and their derivatives) in the gas phase, which may be the formation route of carbon dust grains in space. In this work, the gas-phase ion–molecule collision reaction between fullerene cations (${\rm C}_{n}\, ^+$, n = 32, 34,…, 60) and functionalized PAH molecules (9-hydroxyfluorene, C13H10O) are investigated both experimentally and theoretically. The experimental results show that fullerene/9-hydroxyfluorene cluster cations are efficiently formed, leading to a series of large fullerene/9-hydroxyfluorene cluster cations (e.g. [(C13H10O)C60]+, [(C13H10O)3C58]+, and [(C26H18O)(C13H10O)2C48]+). The binding energies and optimized structures of typical fullerene/9-hydroxyfluorene cluster cations were calculated. The bonding ability plays a decisive role in the cluster formation processes. The reaction surfaces, modes, and combination reaction sites can result in different binding energies, which represent the relative chemical reactivity. Therefore, the geometry and composition of fullerene/9-hydroxyfluorene cluster cations are complicated. In addition, there is an enhanced chemical reactivity for smaller fullerene cations, which is mainly attributed to the newly formed deformed carbon rings (e.g. 7 C-ring). As part of the co-evolution network of interstellar fullerene chemistry, our results suggest that ion–molecule collision reactions contribute to the formation of various fullerene/9-hydroxyfluorene cluster cations in the interstellar medium, providing insights into different chemical reactivity caused by oxygenated functional groups (e.g. hydroxyl, OH, or ether, C-O-C) on the cluster formations.

Gas Phase Hydrogenated and Deuterated Fullerene Cations

H/D accretion, especially onto ionized fullerenes, is expected to be very efficient in space. In this work, we study hydrogenated and deuterated fullerene cations and their photodissociation behavior in the gas phase. The experimental results show that hydrogenated fullerene cations (i.e., [C60H n ]+ and [C70H n ]+, n up to 30) and deuterated fullerene cations (i.e., [C60D n ]+ and [C70D n ]+, n up to 21) are formed efficiently through the ion-atom collision reaction pathway. Upon irradiation, the hydrogenated and deuterated fullerene cations dissociate into fullerene cations and H/H2 or D/D2 species. The structures of the newly formed hydrogenated and deuterated fullerene cations (C58 and C60) and the bonding energies for these reaction pathways are investigated by means of quantum chemical calculations. The competition between hydrogenation and dehydrogenation is confirmed, and the hydrogenation-to-dehydrogenation ratio in the accretion processes in the gas phase is determined. We infer that the proportion of accreted hydrogen and deuterium atoms on the surface of fullerenes is similar to that of hydrogen and deuterium atoms in the interstellar environment where these fullerenes are located, especially when the interstellar environments are similar to our experimental conditions, i.e., the hot environment.

Coevolution of the interstellar chemistry: gas-phase laboratory formation of hydrogenated fullerene-PAH clusters

ABSTRACT Fullerene molecules are affected and constrained by different interstellar environmental factors, such as UV radiation, atoms, and other coexisting molecules. To understand the coevolution of the interstellar fullerene chemistry, by tracking the accretion processes on fullerene cations, we present an investigation of the chemical reactivity of fullerene (C60) cations and smaller fullerene (C54/56/58) cations with hydrogen and C14H10 in the gas phase. Experiments are performed using a quadrupole ion trap in combination with time-of-flight mass spectrometry. The experimental results show hydrogenated fullerene-C14H10 cluster cations (i.e. [Hn C60(C14H10)m ]+ and [Hn C54/56/58(C14H10)m ]+) are efficiently formed through ion-molecule collision reaction. H-atoms are more likely to accumulate on the surface of fullerenes than C14H10; not only does hydrogen more easily form a covalent bond, the later accreted hydrogen will also expel the already accreted C14H10. Through theoretical calculations, we obtain the structure of newly formed clusters (e.g. [HC60(C14H10)]+ and [HC58(C14H10)]+) and the binding energies of their reaction pathways, together with IR spectra. The bonding ability plays a decisive role in the ternary cluster formation processes, and the existence of occupation and expulsion competitive reaction channels in the accretion processes on fullerene surfaces is confirmed. As part of the coevolution of the interstellar chemistry, the occupation and expulsion reaction modes should be considered when fullerenes further react with H-atoms and PAHs. As a result, the molecular structures of hydrogen/fullerene/PAH clusters are diverse, and hydrogenated-fullerene-related clusters (e.g. hydrogenated fullerenes or hydrogenated fullerenes-PAHs) have a higher distribution than non-hydrogenated-fullerene-related clusters (e.g. fullerenes or fullerenes-PAHs) in the interstellar environment.

Gas-phase formation of cationic fullerene/9-aminoanthracene clusters: an indicator for interstellar dust growth

ABSTRACT Growth of clusters by adduction of monomers – as the first step in dust particle growth – is an area of much interest in astronomy. We focus on the fullerene/9-aminoanthracene cluster species, to illustrate the competition between the van der Waals bonding growth and the covalent bonding growth model versus the charge transfer model in the large cluster formation process. The experimental results show that fullerene-fragment (C56 and C58)/9-aminoanthracene cluster cations, e.g. [(C14H11N)nC56]+ and [(C14H11N)nC58]+, n = [1,7], are efficiently formed, while C$_{60}^+$ is insensitive to the cluster’s formation. With laser irradiation, all the fullerene/9-aminoanthracene clusters dissociate into 9-aminoanthracene and fullerene cations. The mechanisms for the reactions of fullerene cations and 9-aminoanthracene were investigated by theoretical calculations, under the assumption that the molecular geometries found for the formed complexes correspond to the global energy minima: the absence of C$_{60}^+$ clusters is mainly due to the charge transfer channel’s competition; [(C14H11N)C58]+ has three types of isomers, with van der Waals or covalent bonds, mainly depending on the reaction sites of fullerene cations. Importantly, in the size grown process, for the fullerene/9-aminoanthracene cluster there exists a geometry configuration conversion between the van der Waals and covalent bonding modes. The largest fullerene/9-aminoanthracene clusters, e.g. [(C14H11N)7C58]+ (240 atoms, ∼4 nm in size), are likely in a multishelled geometry, i.e. seven 9-aminoanthracene molecules surrounding fullerene cations in two layers, which can directly build the relationship between molecular clusters and carbonaceous grains. Nitrogen matters! The specific side chains (e.g. –NH2) play an important role in the growth of interstellar dust.

Gas-phase Formation of Cationic Fullerene/Amino Acid Clusters: Evidence for the “Magic Number” Chemical Reactivity of Fullerene Cations

Abstract An experimental and theoretical investigation on the chemical reactivity of fullerene cations (C n +, n = [36, 60]) with amino acid molecules (e.g., isoleucine, C6H13NO2) is performed. The results show that, in the gas phase, fullerene cations can react with amino acid molecules to form fullerene/amino acid cluster cations with high efficiency. The formation rate constants for the ion–molecule collision reactions between fullerene cations and isoleucine are estimated under the pseudo-first-order reaction condition. We find the formation rate constants increase gradually with a declining C-atom number of fullerene cations (C n +, n = [46, 60]), and depict a plateau in the reactivity for smaller fullerene cations (C n +, n = [36, 44]). More importantly, by comparing to its neighbor fullerenes, the magic number of C-atom counts (54, 58) that process with enhanced chemical reactivity are determined. We also obtained the molecular structures and binding energies for the fullerene-monoisoleucine adducts by quantum chemical calculations, which give a good explanation for the magic number chemical reactivity and the enhanced chemical reactivity of smaller fullerene cations. We infer that our results demonstrate the importance of ion–molecule reactions to the formation of large and complex fullerene-amino acid derivatives in the ISM. The high reactivity of fullerene species may indicate that amino acid molecules or other related prebiotic compounds can accrete on small interstellar carbon dust grains.

Buckyball as an Electron Donor in a Dyad of C60 and Xanthene Dye

AbstractWe successfully achieved the synthesis of C60‐xanthlium, X60_NTf2, where fullerene is an electron donor and xanthlium is an electron acceptor. When the precursor compound X60‐OH was excited at 550 nm, the C60 emission was observed at 715 nm. On the other hand, the fluorescence of X60_NTf2 was completely quenched under the same conditions, suggesting that photo‐induced intramolecular electron transfer (ET) occurred from the singlet excited state of C60. The electrochemical measurement proved that the X60_NTf2 is exothermically possible of ET reaction from 1C60* to xanthylium to form C60.+. Density functional theory (DFT) calculations support the acceptor ability of the xanthylium by showing that the coefficients of the lowest unoccupied molecular orbital (LUMO) were on xanthene moiety. This is a well‐arranged model compound to investigate the properties of transiently generated fullerene radical cations.

Laboratory study of the formation of fullerene (from smaller to larger, C44 to C70)/anthracene cluster cations in the gas phase

The formation and evolution mechanism of fullerenes in the planetary nebula or in the interstellar medium are still not understood. Here, we present the study on the cluster formation and the relative reactivity of fullerene cations (from smaller to larger, C44 to C70) with anthracene molecule (C14H10). The experiment is performed in an apparatus that combines a quadrupole ion trap with a time-of-flight mass spectrometer. By using a 355 nm laser beam to irradiate the trapped fullerenes cations (C60 + or C70 +), smaller fullerene cations C(60 – 2n) +, n = 1 – 8 or C(70 – 2m) +, m = 1 – 11 are generated, respectively. Then reacting with anthracene molecules, series of fullerene/anthracene cluster cations are newly formed (e.g., (C14H10)C(60 – 2n) +, n = 1 – 8 and (C14H10)C(70 – 2m) +, m = 1 – 11), and slight difference of the reactivity within the smaller fullerene cations are observed. Nevertheless, smaller fullerenes show obviously higher reactivity when comparing to fullerene C60 + and C70 +. A successive loss of C2 fragments mechanism is suggested to account for the formation of smaller fullerene cations, which then undergo addition reaction with anthracene molecules to form the fullerene-anthracene cluster cations. It is found that the higher laser energy and longer irradiation time are key factors that affect the formation of smaller fullerene cations. This may indicate that in the strong radiation field environment (such as photon-dominated regions) in space, fullerenes are expected to follow the top-down evolution route, and then form small grain dust (e.g., clusters) through collision reaction with co-existing molecules, here, smaller PAHs.

(Invited) Highly Selective and Scalable Fullerene-Cation-Mediated Synthesis Accessing Cyclo[60]Fullerenes with 5-Membered-Carbon-Ring and Their Application to Perovskite Solar Cells

Fullerene and its derivatives have attracted much attention owing to their versatile applicability in the fields of photovoltaics, bioscience, and space science. In thin-film photovoltaics, cyclo[60]fullerenes have been used as electron acceptors in organic solar cells and as electron-transporting layers (ETLs) in perovskite solar cells. In particular, cyclo[60]fullerenes as an over-coating layer of metal oxide ETLs have been one of the most exploited applications in perovskite solar cells, demonstrating a dramatic reduction hysteresis and enhancement of the device charge-dynamics. With respect to such applications, heterocyclo[60]fullerene, which is one of the most abundant types of cyclo[60]fullerene, have shown relatively poor performance compared with full-carbon-ring cyclo[60]fullerenes because of their electrochemical instability. Accordingly, cyclo[60]fullerenes with a full-carbon-ring, such as 3-membered-carbon-rings (e.g. PC61BM) and 6-membered-carbon-rings (e.g. ICBA, MIF),have been the preferred choices for the over-coating layers of metal oxide ETLs. Yet, cyclo[60]fullerenes with a 5-membered-carbon-ring, namely indano[60]fullerenes, have never been demonstrated to date. This is because the existing synthetic methods exhibit low yields and a limited substrate scope of fullerene derivatives. In this work, we report a cyclo[60]fullerene synthesis mediated by fullerene-cation intermediates, which accesses cyclo[60]fullerenes with a 5-membered-carbon-ring in scalable yields. The fullerene-cation-mediated reactions can render more facile and controlled derivatization of fullerenes than conventional fullerene-anion-mediated or fullerene-radical-mediated reactions. This is because the fullerene-cation-mediated reaction harnesses in situ-generated fullerene cations, which are highly reactive due to exceptionally low energy level of the newly formed lowest unoccupied molecular orbitals (LUMOs). Such high reactivity of the intermediates leads to high selectivity, thus a scalable yield with an excellent functional group tolerance. Accordingly, this fullerene-cation-mediated methodology enabled the production of rare fullerenes, indano[60]fullerene derivatives in this work. The synthesis of indano[60]fullerenes showed high yields as expected (the highest ca. 93%). The mechanism of this new synthetic route was investigated and discussed as well. Moreover, we explored the device application of indano[60]fullerenes in perovskite solar cells as 3- or 6-membered-carbon-rings and 5-membered-heteroatom-rings have been widely used in devices. We found that the hydrophobicity, solubility, reorganization energy of fullerene, and the ability to passivate the perovskite interface were crucial in obtaining high power conversion efficiency (PCE). Among different fullerene derivatives synthesized in this work, indano[60]fullerene (5a) gave a PCE of 20.7% when used as the over-coating layer in perovskite solar cells. The obtained PCE was higher than 19.0% and 16.5% of the reference devices in which C60 and PC61BM were used, respectively. Not only was it, the efficiency of 20.7% stands the highest among the reported fullerene over-coating ETL-based NH3CH3PbI3(MAPbI3)-used perovskite solar cells. Figure 1

Synthesis of Benzothieno[60]fullerenes through Fullerenyl Cation Intermediates.

Benzothieno[60]fullerenes were synthesized using fullerenyl cations as key intermediates. The reaction proceeded through a nucleophilic attack of the sulfur atom as a weak nucleophile to the fullerenyl cation electrophile. A monoarylated fullerene, (2-methylthiophenyl)hydro[60]fullerene, C60ArH (Ar = C6H4-SMe-2 and so on; four derivatives) was subjected to deprotonation with KO tBu to form a fullerenyl anion ArC60-, followed by oxidation using I2 to generate a fullerenyl cation ArC60+, leading to intramolecular demethylative cyclization via fullerene cation-S interaction to the product. Electrochemical and computational studies revealed slightly narrower band gap of this compound than usual fullerene derivatives because of the relatively high-lying HOMO of the fused thieno moiety.

Modulating stability of functionalized fullerene cations [R-C60 ]+ with the nature of R-group.

In this study, the first comprehensive theoretical investigation of the stability of functionalized fullerene-based cations [R-C60 ]+ and its relationship with the nature of the attached R-group was performed. C60 -Fullerene core was functionalized with an alkyl group of different length (R = (CH2 )n CH3 , where n = 0-9). This set was further complemented by bulky isopropyl and tert-butyl and conjugated phenyl groups. A detailed study of the relative stability of target cationic species was accompanied by in-depth investigation of their electronic structure and aromaticity using a large set of descriptors of different nature. The stability of target species was considered with respect to two alternative and competing mechanisms of bond breaking, namely, heterolytic ([R-C60 ]+ → R+ + C60 ) and homolytic ([R-C60 ]+ → R• + C60 +• ) ones. The transformation of strained sp2 -carbon atom in unperturbed C60 -fullerene to nonconstrained tetrahedral sp3 -type in functionalized derivatives was found to be the driving force for the formation of its functionalized cations. In spite of the fact that all systems under consideration were found to be corresponding to local minima on corresponding potential energy surfaces, the functionalization of C60 -core with the smallest and simplest methyl group resulted in most stable compound, as evaluated by bonding energy between R+ and fullerene fragment (in the light of both mechanisms). Subsequent elongation of the alkyl chain or introducing bulky groups led to notable decrease of the bonding energy and, as consequence, of the stability within the framework of heterolytic bond cleavage, whereas homolytic pathway assumes opposite-slight increase of stability along with lengthening of the R-group. The orbital interaction (ΔEorb ) was identified as the main driving force for these trends. In general, the homolytic path was found to be dominating for small-length R-groups such as those with n = 0 and 1. At n = 2, heterolytic and homolytic pathways are equally probable (the difference in corresponding bonding energies is about 1 kcal/mol). However, when the alkyl chain becomes longer (n = 3-9), the cationic bond cleavage appears as the most energetically favorable. © 2018 Wiley Periodicals, Inc.

Functionalization of [60]fullerene through fullerene cation intermediates.

Fullerene cations, namely [60]fullerene radical cation (C60˙+) and organo[60]fullerenyl cation (RC60+), are less investigated as intermediates in synthetic fullerene chemistry because of the intrinsic electronegativity of C60. Remarkably, these two intermediates can mediate reactions that afford versatile, unique and unexpected fullerene derivatives. This review article mainly describes these C60˙+ and RC60+ intermediates and includes a variety of topics, from the generation of C60˙+ and RC60+ species to their applications in fullerene modification reactions, such as Friedel-Crafts hydroarylation, nucleophilic addition, dimerization, intramolecular rearrangement reactions, and intramolecular cyclization reactions. Additionally, this review deeply discusses the mechanism of the formation of unique [60]fullerene derivatives involving [60]fullerene radical cation and organo[60]fullerenyl cation intermediates. In addition, the electrochemical properties and photovoltaic performance of these fullerene derivatives produced through C60˙+ or RC60+-mediated reactions are discussed in this review.

Fullerene cation-mediated demethylation/cyclization to give 5- and 7-membered cyclo[60]fullerene derivatives

Fullerene cations undergo demethylative cyclization through onium intermediates to give cyclo[60]fullerene derivatives for organic solar cell application.

Atomically resolved phase transition of fullerene cations solvated in helium droplets.

Helium has a unique phase diagram and below 25 bar it does not form a solid even at the lowest temperatures. Electrostriction leads to the formation of a solid layer of helium around charged impurities at much lower pressures in liquid and superfluid helium. These so-called ‘Atkins snowballs' have been investigated for several simple ions. Here we form HenC60+ complexes with n exceeding 100 via electron ionization of helium nanodroplets doped with C60. Photofragmentation of these complexes is measured by merging a tunable narrow-bandwidth laser beam with the ions. A switch from red- to blueshift of the absorption frequency of HenC60+ on addition of He atoms at n=32 is associated with a phase transition in the attached helium layer from solid to partly liquid (melting of the Atkins snowball). Elaborate molecular dynamics simulations using a realistic force field and including quantum effects support this interpretation.

Fullerene ion chemistry: a journey of discovery and achievement.

An account is provided of the extraordinary features of buckminster fullerene cations and their chemistry that we discovered in our Ion Chemistry Laboratory at York University (Canada) during a 'golden' period of research in the early 1990s, just after C60 powder became available. We identified new chemical ways of C60 ionization and tracked novel chemistry of C60 (n+) as a function of charge state (n=1-3) with some 50 different reagent molecules. We found that multiple charges enhance reaction rates and diversify reaction products and mechanisms. Strong electrostatic interactions with reagent molecules were seen to reduce barriers to carbon surface bonding and charge-separation reactions, while intramolecular Coulomb repulsion appeared to localize charge on the surface or the substituent and so influence higher order chemistry, including 'spindle', 'star', 'fuzzy ball', 'ball-and-chain' and dimer ion formation. We introduced the notion of 'apparent' gas-phase acidity with measurements of proton-transfer reactions of multiply charged fullerene cations. We also explored the attachment of atomic metal cations to C60 and their subsequent reactions. All these findings were applied to the possible chemistry of fullerene cations in the interstellar medium with a focus on multiply charged fullerene ion formation and the intervention of fullerene cations in fullerene derivatization and molecular synthesis, with a view to their possible future detection.This article is part of the themed issue 'Fullerenes: past, present and future, celebrating the 30th anniversary of Buckminster Fullerene'.

GAS PHASE ABSORPTION SPECTROSCOPY OF AND IN A CRYOGENIC ION TRAP: COMPARISON WITH ASTRONOMICAL MEASUREMENTS*

ABSTRACT Recent low-temperature laboratory measurements and astronomical observations have proved that the fullerene cation is responsible for four diffuse interstellar bands (DIBs). These absorptions correspond to the strongest bands of the lowest electronic transition. The gas phase spectrum below is reported here for the full wavelength range encompassed by the electronic transition. The absorption spectrum of , with its origin band at , has been obtained under similar laboratory conditions. Observations made toward the reddened star were used in a specific search for the absorption of these fullerene cations in diffuse clouds. In the case of , one further band in the astronomical spectrum at is identified, increasing the total number of assigned DIBs to five. Numerous other absorptions in the laboratory spectrum are found to lie below the astronomical detection limit. Special emphasis is placed on the laboratory determination of absolute absorption cross-sections. For this directly yields a column density, , of in diffuse clouds, without the need to rely on theoretical oscillator strengths. The intensity of the electronic transition in the range 7000–8000 Å is spread over many features of similar strength. Absorption cross-section measurements indicate that even for a similar column density, the individual absorption bands of will be too weak to be detected in the astronomical spectra, which is confirmed giving an upper limit of to the equivalent width.

Cage connectivity and frontier π orbitals govern the relative stability of charged fullerene isomers

Fullerene anions and cations have unique structural, electronic, magnetic and chemical properties that make them substantially different from neutral fullerenes. Although much theoretical effort has been devoted to characterizing and predicting their properties, this has been limited to a fraction of isomeric forms, mostly for fullerene anions, and has practically ignored fullerene cations. Here we show that the concepts of cage connectivity and frontier π orbitals allow one to understand the relative stability of charged fullerene isomers without performing elaborate quantum chemistry calculations. The latter is not a trivial matter, as the number of possible isomers for a medium-sized fullerene is many more than 100,000. The model correctly predicts the structures observed experimentally and explains why the isolated pentagon rule is often violated for fullerene anions, but the opposite is found for fullerene cations. These predictions are relevant in fields as diverse as astrophysics, electrochemistry and supramolecular chemistry.

Adsorption of helium on isolated C60 and C70 anions

Adsorption of helium on free, negatively charged fullerenes is studied in this work. Helium nanodroplets have been doped with fullerenes and ionised by electron attachment. For suitable experimental conditions, C−60 and C−70 anions are found to be complexed with a large number of helium atoms. Prominent anomalies in the ion abundances indicate the high stability of the commensurate 1×1 phase in which all hollow adsorption sites are occupied by one atom each. The adsorption energy for an additional helium atom is about 40% less than for atoms in the commensurate layer, similar to our previous findings for fullerene cations and in agreement with theoretical dissociation energies. Similarly, an anomaly in the adsorption energy occurs when 60 helium atoms are attached to C−60 or 65 to C−70. For C60, the anomaly coincides with the one observed for cationic complexes but for C70 it does not. Implications of these features are discussed in light of several theoretical studies of neutral and positively charged helium–fullerene complexes.

Erratum: “Communication: Two-step explosion processes of highly charged fullerene cations C60q+ (q = 20–60)” [J. Chem. Phys. 141, 121105 (2014)

Erratum: “Communication: Two-step explosion processes of highly charged fullerene cations C60<i>q</i>+ (<i>q</i> = 20–60)” [J. Chem. Phys. <b>141</b>, 121105 (2014)

Communication: Two-step explosion processes of highly charged fullerene cations C60q+ (q = 20–60)

To establish the fundamental understanding of the fragmentation dynamics of highly positive charged nano- and bio-materials, we carried out on-the-fly classical trajectory calculations on the fragmentation dynamics of C60(q+) (q = 20-60). We used the UB3LYP/3-21G level of density functional theory and the self-consistent charge density-functional based tight-binding theory. For q ≥ 20, we found that a two-step explosion mechanism governs the fragmentation dynamics: C60(q+) first ejects singly and multiply charged fast atomic cations C(z+) (z ≥ 1) via Coulomb explosions on a timescale of 10 fs to stabilize the remaining core cluster. Thermal evaporations of slow atomic and molecular fragments from the core cluster subsequently occur on a timescale of 100 fs to 1 ps. Increasing the charge q makes the fragments smaller. This two-step mechanism governs the fragmentation dynamics in the most likely case that the initial kinetic energy accumulated upon ionization to C60(q+) by ion impact or X-ray free electron laser is larger than 100 eV.

General treatment of the multimode Jahn–Teller effect: study of fullerenecations

A general model for the analysis of the Adiabatic Potential Energy Surfaces (APES) of the molecules that are subject to the multimode Jahn-Teller effect is presented. The method utilizes the information obtained by DFT calculations on a distorted stationary point on the APES. The essence of the model is to express the distortion along a model minimal energy path called Intrinsic Distortion Path (IDP), projecting the geometry of the system on the normal modes of the either high-symmetry (HS) or low symmetry (LS) nuclear configuration. This allows us to determine the significance of all of the involved normal modes along a relevant particular path of distortion, and the direct calculation of the vibronic coupling constants. The IDP analysis is illustrated by the discussion of the multimode H ⊗ (g + 2h) JT effect in fullerene cations (C(60)(+)) giving a deep insight into the origin and the mechanism of vibronic coupling in fullerene based molecules.