Radical Single-Molecule Junctions

Abstract

Radicals are unique molecular systems for applications in electronic devices due to their open-shell electronic structures. Radicals can function as good electrical conductors and switches in molecular circuits while also holding great promise in the field of molecular spintronics. However, it is both challenging to create stable, persistent radicals and to understand their properties in molecular junctions. The goal of this Perspective is to address this dual challenge by providing design principles for the synthesis of stable radicals relevant to molecular junctions, as well as offering current insight into the electronic properties of radicals in single-molecule devices. By exploring both the chemical and physical properties of established radical systems, we will facilitate increased exploration and development of radical-based molecular systems.

Sufficient driving force for quinoidal isoindigo-based diradicaloids with tunable diradical characters

“…There has been an increasing effort to design and synthesize stable p-conjugated diradicaloids by the kinetic blocking of radical centers and/or thermodynamic stabilization by the introduction of electron-withdrawing substituents and spin delocalization. 8 A large number of persistent and stable diradicaloids have been rationally designed and synthesized, such as quinoidal oligothiophenes and p-extended quinodimethanes (QDMs), diphenalenyl compounds, heteroacenes, indeno-derivatives, rylene ribbons and their tetracyano derivatives, as well as typical donor-acceptor systems. 5,[9][10][11][12][13] The embedded Kekule-type quinoidal resonance structures, para-QDM, and their extended derivatives help to enhance diradical characters.…”

Au-Thiolate Interfacial Coordination: The Key to Determining the Spin State of a Blatter Radical When Incorporated into Gold–Molecule–Gold Junctions

“…Single-molecule electronics, intending to take full advantage of the molecular characteristics to design and manufacture functional electronic devices, offers an alternative option to conventional silicon-based microelectronics. Over the past decades, it has triggered tremendous interest and attention. − Being populated with an odd number of electrons, organic radicals, whose natures provide possibilities for functional devices, have attracted significant interest in single-molecule electronics . First, the open-shell characters of radicals make them promising candidates in molecular spintronics and quantum sensing. − Moreover, owing to the presence of low-lying singly occupied molecular orbitals (SOMOs), the appearance of a resonance peak near the Fermi energy, E f , in the transmission spectra can be expected when the radicals are connected to two metallic electrodes .…”

“…These may include high conductance, high Seebeck coefficient, , rectification, , or reversed conductance decay with an increasing length. − In general, isolated radicals are already very sensitive to their surroundings due to the open-shell electronic structure, let alone the radicals sandwiched between two metallic electrodes, which face a more complex electronic environment. In fact, retaining the open-shell electronic configuration of radicals within a junction is one of the greatest challenges to give full play to the characteristics of radicals in single-molecule electronics. , …”

“…1−4 Being populated with an odd number of electrons, organic radicals, whose natures provide possibilities for functional devices, have attracted significant interest in single-molecule electronics. 5 First, the open-shell characters of radicals make them promising candidates in molecular spintronics and quantum sensing. 6−9 Moreover, owing to the presence of low-lying singly occupied molecular orbitals (SOMOs), the appearance of a resonance peak near the Fermi energy, E f , in the transmission spectra can be expected when the radicals are connected to two metallic electrodes.…”

“…In fact, retaining the open-shell electronic configuration of radicals within a junction is one of the greatest challenges to give full play to the characteristics of radicals in single-molecule electronics. 5,19 The 1,2,4-benzotriazin-4-yl radicals, generally known as Blatter radicals (BRs), have attracted a great deal of attention recently because of their rich physical properties, such as ferromagnetic interactions, 20,21 π-spin delocalization, 22 and low excitation energy, 23 just to name a few. Most of all, this class of radicals has extraordinary stability in ambient conditions and can even be stored for months.…”