Mechanical tuning of conductance and thermopower in helicene molecular junctions

Abstract

Helicenes are inherently chiral polyaromatic molecules composed of all-ortho fused benzene rings possessing a spring-like structure. Here, using a combination of density functional theory and tight-binding calculations, it is demonstrated that controlling the length of the helicene molecule by mechanically stretching or compressing the molecular junction can dramatically change the electronic properties of the helicene, leading to a tunable switching behavior of the conductance and thermopower of the junction with on/off ratios of several orders of magnitude. Furthermore, control over the helicene length and number of rings is shown to lead to more than an order of magnitude increase in the thermopower and thermoelectric figure-of-merit over typical molecular junctions, presenting new possibilities of making efficient thermoelectric molecular devices. The physical origin of the strong dependence of the transport properties of the junction is investigated, and found to be related to a shift in the position of the molecular orbitals.

Slow Magnetic Relaxation in Chiral Helicene-Based Coordination Complex of Dysprosium

“…Moreover, [n]-helicene ligands are helically-shaped, so they possess a chirality despite the absence of enantiocenter. Due to these intrinsic properties, this family of ligands is widely employed for various applications, ranging from organic molecular electronics [33], probes for detection of chirality and sensing devices [34] to molecular junction [35].…”

Length enhancement of thermoelectric effects in DNA duplex chains due to quantum interferences

“…In Fig. 6(b) we present the recalculated ZT value versus n using a typical value of phonon thermal conductance j ph ¼ 20pW K À1 [33][34][35][36][37] of similar molecules. It has been shown [32] that in some cases the phonon thermal conductance is inversely proportional to the square of molecule length L, i.e.…”

Nanoscale Organic Thermoelectric Materials: Measurement, Theoretical Models, and Optimization Strategies

“…In some molecules when weak coupling and strong coupling interaction are coexisted, mechanically control could be able to achieve more obvious adjustment of thermoelectric properties. Theoretical studies for a helicene molecular showed that the conductance increased with increasing compressive strain and decreased with increasing tensile strain, whereas the opposite trend was observed for the Seebeck coefficient . The numerical result shown the sign of the Seebeck coefficient can be reversed when the tension and compression states are switched, indicating another way to realize the transition from n‐type to p‐type materials.…”