Wen Jie Ong

Dynamic self-correcting nucleophilic aromatic substitution

AbstractDynamic covalent chemistry, with its ability to correct synthetic dead-ends, allows for the synthesis of elaborate extended network materials in high yields. However, the limited number of reactions amenable to dynamic covalent chemistry necessarily confines the scope and functionality of materials synthesized. Here, we explore the dynamic and self-correcting nature of nucleophilic aromatic substitution (SNAr), using ortho-aryldithiols and ortho-aryldifluorides that condense to produce redox-active thianthrene units. We demonstrate the facile construction of two-, three- and four-point junctions by reaction between a dithiol nucleophile and three different model electrophiles that produces molecules with two, three and four thianthrene moieties, respectively, in excellent yields. The regioselectivity observed is driven by thermodynamics; other connections form under kinetic control. We also show that the same chemistry can be extended to the synthesis of novel ladder macrocycles and porous polymer networks with Brunauer–Emmett–Teller surface area of up to 813 m2 g−1.Dynamic covalent chemistry offers promise for the formation of elaborate extended network materials in high yields, but the limited number of reactions available confines the scope and functionality of the materials synthesized. Now, nucleophilic aromatic substitution has been shown to be reversible, and thus self-correcting, enabling the easy synthesis of sulfur-rich materials.

Redox Switchable Thianthrene Cavitands

National Science Foundation (U.S.). Center for Energy Efficient Electronics Science (Award ECCS0939514)

Tunneling nanoelectromechanical switches

Nanoelectromechanical (NEM) switches have emerged as a promising competing technology to the conventional metal-oxide semiconductor (MOS) transistors. NEM switches exhibit abrupt switching behavior with large on-off current ratios, near-zero off-state leakage currents and sub-threshold slopes below the 60 mV/decade theoretical limit of conventional MOS devices [1]. However, current NEM switches commonly operate at relatively high actuation voltages exceeding 1 V and suffer from failure due to stiction [1]. Reducing the switching gap is a common approach utilized to lower the operating voltage. However, the decrease in the gap size further increases the surface adhesion forces and consequently the possibility of stiction-induced failure.

Electromechanically actuating molecules

Controlled motion at the nanoscale is an emerging avenue for low powered electronics. The necessity for precision at the nanoscale makes organic chemistry an exciting addition to electronics, as organic synthesis is based upon the design and creation of nanoscale and sub-nanoscale structures. We have recently demonstrated the role of organic materials in the development of a nanoelectromechanical (NEM) switch that operates by electromechanical modulation of tunneling current through a switching gap defined by a few nanometer-thick organic molecular layer sandwiched between conductive contacts [1]. In this device, the molecular layer not only facilitates controlled formation of nanoscale switching gaps, but also avoids direct contact of the electrodes to minimize surface adhesion and provides force control at the nanoscale to prevent device failure due to stiction. Recent work has focused on the compression of the molecular layer by an applied electrostatic force between the two electrodes to reduce the tunneling gap. However, we envision next generation devices can contain advanced materials, which undergo electrochemically stimulated shape changes to modulate the tunneling distance and current. In order to achieve large current on-off ratios, the molecules must be capable of producing significant changes in dimension or shape upon electrical stimuli. Herein, we report a few examples of electromechanically actuating molecules.