Nathaniel S. Finney

Fluorescent signaling based on sulfoxide profluorophores: application to the visual detection of the explosive TATP.

The first visual fluorescence-based assay for the peroxide explosive triacetone triperoxide (TATP) is described. The assay is based on a conceptually new fluorescence signaling mechanism, in which nonemissive pyrenyl sulfoxide profluorophores are oxidized to visibly emissive pyrenyl sulfones. Although not without limitations, these first-generation fluorescent probes can provide a visual response to ca. 100 nmol of TATP. In addition, the success of this assay suggests the potential for broader application of aryl sulfoxides in fluorescent chemosensing.

Helquats: A Facile, Modular, Scalable Route to Novel Helical Dications

The synthesis and properties of helical extended diquat (helquat), and derivatives that bear resemblance to diquat and azoniahelicene, was reported. Triyne with elongated tethers connecting the heterocyclic moiety with the pendant alkyne functionalities undergoing cycloisomerization give helquat featuring two seven-membered rings. The seven helquats reported are accessed uniformly in three steps from commercially available starting materials, entailing a Sonogashira coupling, bisquaternization, cycloisomerization, and 2+2+2 cycloisomerization. The evidence for the reversible electrochemical Weiz-type manifold and regular columnar stacks in crystal structures suggest the potential of helquats as electroactive functional elements.

Versatile Precursors for the Synthesis of Enynes and Enediynes

Abstract (Z)-Ethyl 2,3-dibromopropenoate, readily available in multigram quantities, undergoes selective replacement of the β-bromide in coupling reactions with trimethylsilylacetylene to produce the (Z)-enyne 2. This product may be further elaborated to various functionalized enynes of defined geometry or may be coupled with a second acetylenic reactant to produce (Z)-enediynes.

Thiourea-Based Fluorescent Chemosensors for Aqueous Metal Ion Detection and Cellular Imaging

We describe three significant advances in the use of thioureas as reporting elements for metal-responsive fluorescent chemosensors. First, on the basis of the crystal structure of a chemosensor analogue, we provide a deeper understanding of the details of the thiourea coordination environment. Second, we describe a new generation of chemosensors with higher affinities for Zn(2+) and Cd(2+) than were observed for earlier probes, expanding the scope of this type of probe beyond Hg(2+) detection. Third, we show that a thiourea-based chemosensor can be employed for fluorescence microscopy imaging of Hg(2+) ion concentrations in living mammalian cells.

Sulfoxides as Response Elements for Fluorescent Chemosensors

Sulfoxides are shown to be viable reporting groups for fluorescent chemosensor development. Metal coordination of sulfoxide-appended fluorophores suppresses excited-state pyramidal inversion of the sulfoxide, leading to enhanced fluorescence emission. This new structural motif allows the construction of fluorescent chemosensors that do not require nitrogen coordination as part of the signaling process, that have a range of selectivities and affinities for oxophilic metal ions, and that can function in water.

Thioureas as Reporting Elements for Metal-Responsive Fluorescent Chemosensors

Proof that sulfur is a viable reporting element for the development of fluorescent chemosensors for metal ions is presented. To date, the majority of metal-responsive fluorescent chemosensors have relied on metal-nitrogen coordination to provide a fluorescence response, most commonly by suppressing photoinduced electron transfer (PET) quenching. While chemosensors with direct application to biology, medicine, and analytical chemistry have been so developed, reliance on the coordination chemistry of nitrogen remains a practical and conceptual limitation. Building on the fact that thioureas can quench fluorescence emission by PET, it is shown that the quenched emission of thiourea-appended naphthalimides can be restored by metal binding and that metal affinity and selectivity can be controlled through structural modification of the thiourea substituents. Further, such chemosensors can function in aqueous media and, unlike nitrogen-based chemosensors, are unresponsive to increases in [H(+)]. Given that the coordination properties of sulfur are distinct from those of nitrogen, this work lays the foundation for the development of a new class of interesting and useful metal-responsive fluorescent probes.

Synthesis and Evaluation of 2,5-Linked Alternating Pyridine−Thiophene Oligomers

The first iterative access to alternating 2,5-linked pyridine-thiophene (Py-Th) oligomers is presented. These oligomers exhibit strong absorption and emission, even in the solid state (picture of the longest oligomer, above). Protonation leads to large red shifts in emission and, unlike most known thiophene-containing oligomers, they are readily reduced but not oxidized. These species represent a promising new class of materials for further study and potential application.

Efficient Discovery of Fluorescent Chemosensors Based on a Biarylpyridine Scaffold

The discovery of several fluorescent chemosensors for Hg(II) and Ag(I) in mixed aqueous solution is reported. The ease with which these fluorionophores were prepared from a common core underscores the utility of conformational restriction as a signaling mechanism. In addition, for the first time, significant changes were observed in biarylpyridine emission wavelength, allowing ratiometric detection of Hg(II) and Ag(I). Finally, on the basis of computational analyses, beneficial structural modifications were predicted for the next generation of chemosensors.

Allene synthesis from 2-alkyn-1-ols

Abstract Activation of 2-alkyn-1-ols as their methanesulfonate esters and displacement with hydrazine furnishes the corresponding alkynyl hydrazine derivatives which undergo smooth oxidative rearrangement with diethyl azodicarboxylate (DEAD) or 4-methyl-1,2,4-triazoline-3,5-dione (MTAD) to form allenes.

Systematic evaluation of 2,6-linked pyridine-thiophene oligomers.

An efficient synthesis of alternating 2,6-linked pyridine-thiophene (Py-Th) oligomers allows systematic evaluation of their optical and electrochemical properties. The six- and eight-ring oligomers are revealed to be brightly luminescent, even in the solid state. The oligomers are easily reduced but cannot be electrochemically oxidized. The longer oligomers have reduction potentials similar to those reported for pyridine-thiophene polymers of less defined structure. Protonation of the pyridine or substitution at C4 are shown to further modulate the electronic properties and, in combination with the low-lying absolute LUMO energies, these data suggest that the compounds are potential n-type materials worthy of further study.