Other Fluorophores

The widely used near-infrared organic small-molecule fluorophores also include coumarin fluorophores, naphthalimide fluorophores, hybrid fluorophores, porphyrin fluorophores and so on.

Coumarin fluorophores

Introduction

Coumarin and its derivatives have strong fluorescence properties in the visible light region, which makes them useful as laser fuels and nonlinear optical chromophore, as well as good fluorescent brighteners, laser fuels, fluorescent probes and nonlinear optical materials. Coumarin fluorophores are benzopyrone structures, which have the advantages of high fluorescence quantum yield, large Stokes-shift, adjustable photophysical and photochemical properties and good stability, etc. They are excellent fluorophores in the design of fluorescence sensor molecules.

Application

• Hg²⁺ detection: Coumarin fluorophore has been widely used in Hg²⁺ detection probes due to its excellent photophysical and chemical properties. In 2011, Guha ^[1] has synthesized a fluorescent probe with vanillin-coupled coumarin (see fig.1). It has been used for the imaging analysis of Hg²⁺ accumulation in Candida albicans cells.

Fig.1 Proposed binding mode of probe with Hg²⁺

• Biological mercaptan detection: Quantitative detection of biological mercaptan has important medical significance. The probe based on coumarin connects the fluorophore to the tumor cell locator via disulfide bonds, which are easily broken by sulfhydryl group and release the precursor fluorophore, which is commonly used in the detection of biological proteins ^[2].

Fig.2 Schematic diagram of response mechanism between probe and bio-mercaptan

Naphthalene imides fluorophores

Introduction

Naphthalene imides fluorophores have been widely used in the field of fluorescence sensing due to their high fluorescence quantum yield, moderate emission wavelength, large Stokes-shift, good photostability and easy structure modification. Expect that, naphthalimides derivatives, as a kind of fluorescent dyes, also are used in textile, printing and dyeing, ink, coatings and other industries for their excellent dyeing properties, stability and light fastness.

Fig.3 The structure of naphthalimide derivatives

Application

• Small-molecule detection probe: Fu^[3]. has synthesized and reported a two-photon fluorescent probe SnHN-N3 (see fig.4) for H₂S detection, which has advantages over traditional fluorescent probes. Yang J. ^[4] synthesized and reported a fluorescent probe NAD (see fig.5) for the detection of cysteine, which not only has high sensitivity and excellent selectivity, but also has a very low detection limit.

Fig.4 Schematic illustrations of SnHN-N3 with H₂S

Fig.5 Fluorescence response schematic illustration of NAD toward cysteine
• Bio-enzyme assay: Naphthalimide-based fluorophore has been applied to probes to study the enzyme activity in living organisms. Qiang ^[5]. synthesized and reported a two-photon fluorescent probe for the detection of human carboxylesterases 2 (HCE₂), which not only can specifically recognize HCE₂, but also has a very low detection limit with very fast response.

Fig.6 Fluorescence response schematic illustration of probe toward HCE₂

• Metal ion detection: Naphthalimide has stable planar structure, large Stokes-shift and high quantum yield, so it has been selected as a fluorescent group for the construction of fluorescent probe for the detection of Al³⁺ due to its excellent properties. Liu Jing ^[6] has designed and synthesized a fluorescent enhancement probe (NCFP) based on the naphthalene imide derivatives. The results indicate that the fluorescent probe has strong fluorescence responses to Al³⁺, and remarkably high selectivity to Al³⁺ than other metal ions.

Fig.7 Proposed mechanism between probe molecule and Al³⁺

The background and application of coumarin and naphthalimide fluorophores are briefly introduced, Alfa Chemistry also provides other commonly used fluorophores, if you need assistance, please don't hesitate to contact us.

References

1. Guha S.; et al. Vanillin-coumarin hybrid molecule as an efficient fluorescent probe for trace level determination of Hg (II) and its application in cell imaging. Talanta, 2011, 85(3): 1658-1664.
2. Feuster E.K.; et al. Detection of amines and unprotected amino acids in aqueous conditions by formation of highly fluorescent iminium ions. J. Am. Chem. Soc.2003, 125, 16174-16175.
3. Fu Y J.; et al. A cell surface specific two-photon fluorescent probe for monitoring intercellular transmission of hydrogen sulfide. Analytica Chimica Acta, 2017, 994: 1.
4. Yang JJ.; et al. Synthesis of 1, 8-naphthalimide based cysteine fluorescent probe and its application in biological-imaging. Chem. J. Chinese. U, 2017 (7): 198.
5. Jin Q.; et al. ACS Appl Mater Inter, 2015, 7(51): 28474.
6. Liu J.; et al. Synthesis and spectral properties of naphthalimide grafted chitosan fluorescent probe for aluminum Ion. Chinese Journal of Luminescence, 2018, 39(4): 573-579.