Switchable ErSc2N rotor within a C80 fullerene cage: An EPR and photoluminescence excitation study

TL;DR

This study investigates ErSc2N@C80 fullerene using EPR and photoluminescence excitation to observe switchable rotor orientations and spin relaxation mechanisms, revealing photoinduced cage symmetry changes that are metastable at low temperatures.

Contribution

It demonstrates the first observation of photoinduced switching of ErSc2N configurations within a fullerene cage using combined EPR and PLE techniques.

Findings

Two rotor orientations observed in EPR consistent with PLE data.

Photoinduced switching of cage symmetry is metastable at 20 K.

Spin relaxation involves an Orbach process via the first excited state.

Abstract

Systems exhibiting both spin and orbital degrees of freedom, of which Er3+ is one, can offer mechanisms for manipulating and measuring spin states via optical excitations. Motivated by the possibility of observing photoluminescence and electron paramagnetic resonance from the same species located within a fullerene molecule, we initiated an EPR study of Er3+ in ErSc2N@C80. Two orientations of the ErSc2N rotor within the C80 fullerene are observed in EPR, consistent with earlier studies using photoluminescence excitation (PLE) spectroscopy. For some crystal field orientations, electron spin relaxation is driven by an Orbach process via the first excited electronic state of the 4I_15/2 multiplet. We observe a change in the relative populations of the two ErSc2N configurations upon the application of 532 nm illuminations, and are thus able to switch the majority cage symmetry. This photoisomerisation, observable by both EPR and PLE, is metastable, lasting many hours at 20 K.