This work introduces an approach to uncoupling electrons via maximum utilization of localized aromatic units, i.e., the Clar's π-sextets. To illustrate the utility of this concept to the design of Kekulédiradicaloids, we have synthesized a tridecacyclic polyaromatic system where a gain of five Clar's sextets in the openshell form overcomes electron pairing and leads to the emergence of a high degree of diradical character. According to unrestricted symmetry-broken UCAM-B3LYP calculations, the singlet diradical character in this core system is characterized by the y 0 value of 0.98 (y 0 = 0 for a closed-shell molecule, y 0 = 1 for pure diradical). The efficiency of the new design strategy was evaluated by comparing the Kekulésystem with an isomeric non-Kekulédiradical of identical size, i.e., a system where the radical centers cannot couple via resonance. The calculated singlet−triplet gap, i.e., the ΔE ST values, in both of these systems approaches zero: −0.3 kcal/mol for the Kekuléand +0.2 kcal/mol for the non-Kekulédiradicaloids. The target isomeric Kekuléand non-Kekulésystems were assembled using a sequence of radical periannulations, cross-coupling, and C−H activation. The diradicals are kinetically stabilized by six tertbutyl substituents and (triisopropylsilyl)acetylene groups. Both molecules are NMR-inactive but electron paramagnetic resonance (EPR)-active at room temperature. Cyclic voltammetry revealed quasi-reversible oxidation and reduction processes, consistent with the presence of two nearly degenerate partially occupied molecular orbitals. The experimentally measured ΔE ST value of −0.14 kcal/ mol confirms that K is, indeed, a nearly perfect singlet diradical.

Aptamers have been employed as the biorecognition element in electrochemical aptamer-based (E-AB) biosensors, for the detection of a diverse range of analyte molecules, on electrodes with sizescales ranging from a few microns to several millimeters. Simultaneous detection of multiple different analytes requires the selective modification of multiple electrode surfaces with different aptamers. This process is typically achieved by incubating separate macroscale electrodes in a solution with the desired aptamer, which is unsuitable for microelectrode arrays in which the electrodes are closely spaced. In this work, we selectively modified electrode surfaces with thiolated aptamers of different single-stranded DNA sequences, by successive removal and addition of thiol monolayers. This was achieved by electrodesorption of thiol monolayers using controlled potential, to expose unmodified gold electrodes to be modified with a different thiolated aptamer, thus enabling multiple different aptamers to be used on the surfaces of closely spaced microelectrodes. All aptamers were methylene blue terminated, allowing redox currents to be measured and used to monitor aptamer probe packing density on the electrode surface and the selectivity of the sensors. Here, we demonstrate the microscale E-AB sensor multianalyte detection method using aptamers for target analytes, adenosine triphosphate, dopamine, and serotonin, which can ultimately be applied to perform localized simultaneous detection using electrode arrays.

This work introduces an approach to uncoupling electrons via maximum utilization of localized aromatic units, i.e., the Clar’s sextets. To illustrate the utility of this concept to the design of Kekulé diradicaloids, we have synthesized a tridecacyclic polyaromatic system where a gain of five Clar’s sextets in the open shell form overcomes electron pairing and leads to the emergence of high degree of diradical character. According to unrestricted symmetry-broken UCAM-B3LYP DFT calculations, the singlet diradical character in this core system is characterized by the y0 value of 0.98 (y0 = 0 for closed shell molecule, y0 = 1 for pure diradical). The efficiency of the new design strategy was evaluated by comparing the Kekulé system with an isomeric non-Kekulé diradical of identical size, i.e., a system where the radical centers cannot couple via resonance and the high-spin ground state is unavoidable. The calculated singlet-triplet gap, i.e., the 〖ΔE〗_ST values, in both of these systems approach zero: -0.3 kcal/mol for the Kekulé and +0.2 kcal/mol for the non-Kekulé diradicaloids. The target isomeric Kekulé and non-Kekulé systems were assembled using a sequence of radical peri-annulations, cross-coupling and C-H activation. The diradicals are kinetically stabilized by six tert-butyl substituents and (triisopropylsilyl)acetylene groups. The Kekulé diradicaloid (K) has a half-life of 42 h under ambient conditions (i.e., exposure to air at the room temperature) while the non-Kekulé diradicaloid (NK) has a half-life of 2h. Both molecules are NMR-inactive but EPR-active at room temperature. The magnetic properties of the Kekulé diradicaloid was studied by superconducting quantum interference device (SQUID) to provide the experimental singlet-triplet energy gap, 〖ΔE〗_ST (K) = -0.8 kcal/mol, which was close to calculated value. Cyclic voltammetry revealed quasi-reversible two-electron oxidation and reduction processes, consistent with the presence of two degenerate partially occupied molecular orbitals.