Structural control over spin localization in triarylmethyls

Abstract

Triarylmethyls (TAMs) are a class of long-lived purely organic radicals discovered at the beginning of the twentieth century. The chemical versatility and high stability of TAMs have lead to their application in many fields of science and technology. All compounds of this class are composed of three aryl rings bonded to a central carbon atom, where their unpaired electron mainly resides. Due to the π-conjugated electronic nature of this molecular structure, the possibility arises of controlling the unpaired electron localization (i.e. spin localization) by the torsion angles of the three aryl rings. By using density functional theory calculations (DFT) we have carefully investigated this phenomenon for a wide range of TAMs and probed how it is influenced by other important parameters such as chemical functionalization and temperature. Our results demonstrate that a single general spin versus structure relation is followed for all of our studied TAMs confirming that having a predictable structure-dependent spin localisation is an intrinsic feature of these radicals. Considering that spin localisation in TAMs is linked to many other important properties (e.g. magnetic interactions, optical absorption bands, magnetoresistance phenomena), the fact that manipulation of aryl ring twist angles could lead to molecular level control over such features presents enormous potential for future scientific and technological applications.