Structural control over spin localization in triarylmethyls

Abstract

Using density functional theory calculations we demonstrate the existence of a general relation between structure and spin localisation in an important class of organic radicals, and point towards its potential use in future applications.

Design of multi-functional 2D open-shell organic networks with mechanically controllable properties

“…Application of a uniaxial strain to both networks gives rise to a smooth perturbation of the molecular structure within every TAM unit composing the material. In agreement with our previous study on single molecule TAMs, 11 the strain-induced aryl ring twist gives rise to a monotonic and homogeneous change in the spin localization within every radical centre. Accordingly, the electronic and magnetic properties of the materials are also found to change, demonstrating the validity of our approach to design 2D multi-functional materials with externally controllable characteristics.…”

“…1). 11 In this respect, the role of chemical functionalization seems to be limited to determining the aryl ring twist angles due to steric hindrance, but other effects such as the electro-donating/withdrawing nature of substituents play a secondary role. The same steric repulsion, as determined by chemical functionality, also determines the rotational freedom of the three aryl rings and thus the ease with which their twist angles may be externally manipulated.…”

“…4d) should give rise to a net change in spin localization within every radical centre within the networks as found for single TAM molecules. 11 By examining the spin density distribution for the relaxed (Fig. 5a) and most stretched (Fig.…”

“…1). 11 Based on π-overlap arguments, 20–23 we found that a linear relationship exists between the spin density on αC and the average of the cosine squared of the three dihedrals (cos 2   φ = (cos 2   φ 1 + cos 2   φ 2 + cos 2   φ 3 )/3). Moreover, we found that this relationship is independent of both the chemical functionalization of the considered TAM derivative and the system's temperature.…”

“…31–37 In a very similar way, externally applied strain onto a suitably designed TAM-based material could induce an aryl ring twist within every TAM unit composing the material's skeleton which, in turn, should open the possibility of externally controlling its most fundamental characteristics. 11 External manipulation of aryl ring twist angles in π-conjugated materials though, as far as we know, has not yet been experimentally achieved, highlighting the challenging task that it represents. To accomplish this objective there are some important criteria regarding the structural characteristics of the TAM-based material to be designed:…”