Insight on Mercapto-Coumarins: Synthesis and Reactivity

Mercapto (or sulfanyl)-coumarins are heterocycles of great interest in the development of valuable active structures in material and biological domains. They represent a highly exploitable class of compounds that open many possibilities for further chemical transformations. The present review aims to draw focus toward the synthetic applicability of various forms of mercapto-coumarins and their representations in pharmaceuticals and industries. This work covers the literature issued from 1970 to 2021.

How Fast Can Thiols Bind to the Gold Nanoparticle Surface?

Kinetics of gold nanoparticle surface modification with thiols can take more than one hour for completion. 7-mercapto-4-methylcoumarin can be used to follow the process by fluorescence spectroscopy and serves as a convenient molecular probe to determine relative kinetics. SERS studies with aromatic thiols further support the slow surface modification kinetics observed by fluorescence spectroscopy. The formation of thiolate bonds is a relatively slow process; we recommend one to two hour wait for thiol binding to be essentially complete, while for disulfides, overnight incubation is suggested.

Photophysics of 7-mercapto-4-methylcoumarin and derivatives: complementary fluorescence behaviour to 7-hydroxycoumarins

The photophysical behaviour of 7-mercapto-4-methylcoumarin (C-SH) and derivatives has been studied in different solvents. In contrast to 7-hydroxy-4-methylcoumarin, C-SH shows poor emission, but high fluorescence when the thiol is alkylated. The origin and character of the lowest singlet states are discussed, specifically proposing that the thione-like C[double bond, length as m-dash]S resonance form plays a key role in excited state deactivation in C-SH.

Suppressed blinking behavior of CdSe/CdS QDs by polymer coating

Semiconductor quantum dots (QDs) are very important fluorescent nanocrystals with excellent optical properties. However, QDs, at the single-particle level, show severe fluorescence intermittency (or blinking) on a wide time scale from milliseconds to minutes, which limits certain optical and biological applications. Generally, blinking behavior of QDs strongly depends on their surface state and surrounding environment. Therefore, current blinking suppression approaches are mostly focused on the introduction of an inorganic shell and organic small molecule compounds. In this study, we described a "bottom up" approach for the synthesis of CdSe/CdS/polymer core/shell/shell QDs via the in situ one-pot polymerization approach in order to control the blinking behavior of QDs. Three monomers (dithiothreitol (DTT), phenylenediamine (PDA), and hexamethylenediamine (HDA)) were respectively used to polymerize with hexachlorocyclotriphosphazene (HCCP), and then the polyphosphazene polymers were obtained with cyclotriphosphazene as the basic macromolecular backbone. By regulating the molar ratios of the activated comonomers, we can control the blinking behavior of CdSe/CdS/polymer QDs. Under the optimal conditions, the percentage of "non-blinking" CdSe/CdS/polymer QDs (the "on time" fraction > 99% of the overall observation time) was up to 78%. The suppression mechanism was attributed to the efficient passivation of QD surface traps by the sulfhydryl or phenyl groups in the polyphosphazene polymers.

Doubly-dynamic-covalent polymers composed of oxime and oxanorbornene links

Two sets of reversible covalent linkages distributed in series along a polymer backbone were used to prepare a new class of doubly dynamic-covalent polymers capable of reversibly dissociatingviatwo distinct pathways.

pH-Responsive quantum dots (RQDs) that combine a fluorescent nanoparticle with a pH-sensitive dye

A quantum dot conjugated to a dye through an experimentally simple process of self-assembly exhibits an enhanced emission when the dye is attached, and this effect is pH-sensitive.

The properties and performance of a pH-responsive functionalised nanoparticle

We report fluorescence measurements of three quantum dots (QDs) of different sizes functionalised with the same pH responsive naphthalimide dye. QD size strongly influences energy transfer between dye and dot. Using QDs with an emission maximum of 570 nm gives rise to an interesting transfer of energy from dye to dot, while QDs with an emission maximum at 670 nm give unexpected enhancement of the dye emission. Titrations of QDs with the dye provide a means to establish the loading and hence an approximation of the surface dye density, which varies in proportion to QD size. Quenching effects are observed beyond the loading limit, and may indicate non-specific interactions between the excess dye and the nanoparticle. Attachment of the dye to the QD core is achieved by a thiol/disulfide exchange process that has been interrogated with Raman spectroscopy. The stability of these QD–dye conjugates over time and across a physiological pH range has been investigated to provide an assessment of their performance and robustness.