High-pressure infrared transmission measurements on (Ph4P)2IC60 were performed up to 9 GPa over a broad frequency range (200 -20000 cm −1 ) to monitor the vibrational and electronic/vibronic excitations under pressure. The four fundamental T1u modes of C − 60 are split into doublets already at the lowest applied pressure and harden with increasing pressure. Several cation modes and fullerene-related modes split into doublets at around 2 GPa, the most prominent one being the G1u mode. The splitting of the vibrational modes can be attributed to the transition from the dynamic to static Jahn-Teller effect, caused by steric crowding at high pressure. Four absorption bands are observed in the NIR-VIS frequency range. They are discussed in terms of transitions between LUMO electronic states in C − 60 , which are split because of the Jahn-Teller distortion and can be coupled with vibrational modes. Various distortions and the corresponding symmetry lowering are discussed. The observed redshift of the absorption bands indicates that the splitting of the LUMO electronic states is reduced upon pressure application.

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We report the Jahn-Teller (JT) dynamics of the C À 60 monoanion under pressure in (Ph 4 P) 2 IC 60 . (Ph 4 P) 2 IC 60 was synthesized by electrochemical crystallization and investigated by infrared transmission measurements up to 5 GPa. The behavior of two T 1u vibrational modes of C À 60 , which exhibit signatures of the dynamic JT effect at ambient conditions, was followed under pressure. The pressureinduced transition from the dynamic to the static JT state was observed at $2 GPa. Due to symmetry lowering related to the dynamic JT effect, the G 1u mode is activated and shows a splitting at the pressure-induced dynamic-to-static JT distortion. 1 Introduction C 60 -fullerene, the highly symmetric system in nature has kindled interest among the scientific community, to investigate its intriguing properties. The neutral C 60 molecule crystallizes in face-centered cubic (fcc) structure at room temperature and has large enough interstitial space for doping with alkali metals. Several fullerene-related compounds were synthesized and have been investigated. With appropriate doping, the properties of C 60 can be tuned from insulating to superconducting state or even magnetic. Doping C 60 with electrons induces interesting properties in the corresponding compounds: metallic superconducting phases A 3 C 60 (where A stands for alkali metal), semiconducting A 4 C 60 or ferromagnetic TDAE-C 60 which are governed by various physical phenomena [1,2].(Ph 4 P) 2 IC 60 (C 60 -tetraphenylphosphoniumiodide) is one of the charge transfer salts, synthesized by electrochemical method [3]. This fully ionic (Ph 4 P) 2 IC 60 is air stable. (Ph 4 P) 2 IC 60 is tetragonal with space group I 4/m . The I 4/m space group sustains two geometrically equivalent orientations of the C