Pressure-induced transition from the dynamic to static Jahn-Teller effect in (Ph$_{4}$P)$_{2}$IC$_{60}$

TL;DR

This study investigates how high pressure induces a transition from dynamic to static Jahn-Teller effects in ext{(Ph}_4 ext{P)}_2 ext{IC}_{60}, revealing vibrational mode splitting and electronic state changes through infrared spectroscopy.

Contribution

It provides the first detailed high-pressure infrared analysis of Jahn-Teller effects in ext{(Ph}_4 ext{P)}_2 ext{IC}_{60}, linking vibrational and electronic changes to pressure-induced structural distortions.

Findings

Vibrational modes split into doublets at low pressure, indicating static Jahn-Teller effect onset.

Electronic LUMO states show reduced splitting under pressure, evidenced by redshifted absorption bands.

Pressure causes symmetry lowering and vibrational mode splitting consistent with a transition from dynamic to static Jahn-Teller distortion.

Abstract

High-pressure infrared transmission measurements on \PhC60 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 T$_{1u}$ modes of \C60a\ 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 G$_{1u}$ 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 \C60a, 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.