Normal & reversed spin mobility in a diradical by electron-vibration coupling

Yi Shen,Fang Miao,Dongsheng Wang,Fabrizia Negri,Yonghao Zheng,Yasi Dai,Sergio Moles Quintero,Juan Casado,Hanjiao Chen,Guodong Xue

doi:10.1038/s41467-021-26368-8

Abstract

π−conjugated radicals have great promise for use in organic spintronics, however, the mechanisms of spin relaxation and mobility related to radical structural flexibility remain unexplored. Here, we describe a dumbbell shape azobenzene diradical and correlate its solid-state flexibility with spin relaxation and mobility. We employ a combination of X-ray diffraction and Raman spectroscopy to determine the molecular changes with temperature. Heating leads to: i) a modulation of the spin distribution; and ii) a “normal” quinoidal → aromatic transformation at low temperatures driven by the intramolecular rotational vibrations of the azobenzene core and a “reversed” aromatic → quinoidal change at high temperatures activated by an azobenzene bicycle pedal motion amplified by anisotropic intermolecular interactions. Thermal excitation of these vibrational states modulates the diradical electronic and spin structures featuring vibronic coupling mechanisms that might be relevant for future design of high spin organic molecules with tunable magnetic properties for solid state spintronics.

Highlights

Π−conjugated radicals have great promise for use in organic spintronics, the mechanisms of spin relaxation and mobility related to radical structural flexibility remain unexplored
On the way to uncover the fundamental properties of the spin in the organic matter, an important feature is the description of the connections between structural flexibility of π-conjugated molecules and spin delocalization and dynamics in the flexible backbone
In diradicals and in π-conjugated molecules, one always observes a continuum in the “normal” quinoidal→aromatic transformation on heating what makes certainly unexpected this structural A→PQ inversion or “reversed” quinoidal→aromatic transformation we discover in CAR

Summary

Introduction

Π−conjugated radicals have great promise for use in organic spintronics, the mechanisms of spin relaxation and mobility related to radical structural flexibility remain unexplored. Heat absorption provokes the preferential excitation of low energy torsional vibrational modes of the “freer” azobenzene driving the π-conjugated structure towards a more aromatic form, or “normal” quinoidal→aromatic transformation.

Results

Conclusion