Squaraine dye

Last updated
(top) a 1,2,3,3-tetramethyl-3H-indolium salt and (bottom) aniline derivative of squaraine dyes Squarainedyes.png
(top) a 1,2,3,3-tetramethyl-3H-indolium salt and (bottom) aniline derivative of squaraine dyes

Squaraine dyes are a class of organic dyes showing intense fluorescence, typically in the red and near infrared region (absorption maxima are found between 630 and 670 nm and their emission maxima are between 650–700 nm). They are characterized by their unique aromatic four membered ring system derived from squaric acid. Most squaraines are encumbered by nucleophilic attack of the central four membered ring, which is highly electron deficient. This encumbrance can be attenuated by the formation of a rotaxane around the dye to protect it from nucleophiles. They are currently used as sensors for ions and have recently, with the advent of protected squanaine derivatives, been exploited in biomedical imaging.

Fluorescence emission of light by a substance that has absorbed light or other electromagnetic radiation

Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation. It is a form of luminescence. In most cases, the emitted light has a longer wavelength, and therefore lower energy, than the absorbed radiation. The most striking example of fluorescence occurs when the absorbed radiation is in the ultraviolet region of the spectrum, and thus invisible to the human eye, while the emitted light is in the visible region, which gives the fluorescent substance a distinct color that can be seen only when exposed to UV light. Fluorescent materials cease to glow nearly immediately when the radiation source stops, unlike phosphorescent materials, which continue to emit light for some time after.

Squaric acid, also called quadratic acid because its four carbon atoms approximately form a square, is a dibasic organic acid with the chemical formula C4H2O4.

Rotaxane class of chemical compounds

A rotaxane is a mechanically interlocked molecular architecture consisting of a "dumbbell shaped molecule" which is threaded through a "macrocycle". The name is derived from the Latin for wheel (rota) and axle (axis). The two components of a rotaxane are kinetically trapped since the ends of the dumbbell are larger than the internal diameter of the ring and prevent dissociation (unthreading) of the components since this would require significant distortion of the covalent bonds.

Contents

Synthesis

Synthesis of squaraine dyes was reported at least in 1966. [1] They are derived from squaric acid which undergoes an electrophilic aromatic substitution reaction with an aniline or another electron rich derivative to form a highly conjugated product with extensive charge distribution. For instance, squaraine dyes are also formed via reaction of squaric acid or its derivatives with so-called "methylene bases" like 2-methyl-indolenines, 2-methyl-benzthiazoles or 2-methyl-benzo-selenazoles. Indolenine-based squaraines combine good photostability including high quantum yields when bound to proteins and reactive versions of these dyes are commonly used as fluorescent probes and labels for biomedical applications. [2] [3]

Electrophilic aromatic substitution is an organic reaction in which an atom that is attached to an aromatic system is replaced by an electrophile. Some of the most important electrophilic aromatic substitutions are aromatic nitration, aromatic halogenation, aromatic sulfonation, and acylation and alkylating Friedel–Crafts reaction.

Aniline chemical compound

Aniline is an organic compound with the formula C6H5NH2. Consisting of a phenyl group attached to an amino group, aniline is the prototypical aromatic amine. Its main use is in the manufacture of precursors to polyurethane and other industrial chemicals. Like most volatile amines, it has the odor of rotten fish. It ignites readily, burning with a smoky flame characteristic of aromatic compounds.

Squarylium dye III

Structure of squarylium dye Squarylium.GIF
Structure of squarylium dye

Squarylium dyes have poor solubility in most solvents, except for dichloromethane and a few others. Their absorption peaks at ~630 nm and luminescence at ~650 nm. [4] The luminescence is photochemically stable [5] and its quantum yield is ~0.65. [6]

Dichloromethane chemical compound

Dichloromethane (DCM or methylene chloride) is a geminal organic compound with the formula CH2Cl2. This colorless, volatile liquid with a moderately sweet aroma is widely used as a solvent. Although it is not miscible with water, it is polar, and miscible with many organic solvents.

The quantum yield (Φ) of a radiation-induced process is the number of times a specific event occurs per photon absorbed by the system. The "event" is typically a kind of chemical reaction.

Squarylium dye molecules can be encapsulated into carbon nanotubes enhancing the optical properties of carbon nanotubes. [7] Efficient energy transfer occurs between the encapsulated dye and nanotube — light is absorbed by the dye and without significant loss is transferred to the nanotubes. Encapsulation increases chemical and thermal stability of squarylium molecules; it also allows their isolation and individual characterization. For example, encapsulation of dye molecules inside carbon nanotubes completely quenches strong dye luminescence, thus allowing measurement and analysis of their Raman spectra. [8]

Within materials science, the optical properties of carbon nanotubes refer specifically to the absorption, photoluminescence (fluorescence), and Raman spectroscopy of carbon nanotubes. Spectroscopic methods offer the possibility of quick and non-destructive characterization of relatively large amounts of carbon nanotubes. There is a strong demand for such characterization from the industrial point of view: numerous parameters of the nanotube synthesis can be changed, intentionally or unintentionally, to alter the nanotube quality. As shown below, optical absorption, photoluminescence and Raman spectroscopies allow quick and reliable characterization of this "nanotube quality" in terms of non-tubular carbon content, structure (chirality) of the produced nanotubes, and structural defects. Those features determine nearly any other property, such as optical, mechanical, and electrical.

Luminescence emission of light by a substance not resulting from heat

Luminescence is spontaneous emission of light by a substance not resulting from heat; it is thus a form of cold-body radiation. It can be caused by chemical reactions, electrical energy, subatomic motions or stress on a crystal. This distinguishes luminescence from incandescence, which is light emitted by a substance as a result of heating. Historically, radioactivity was thought of as a form of "radio-luminescence", although it is today considered to be separate since it involves more than electromagnetic radiation.

Raman scattering

Raman scattering or the Raman effect is the inelastic scattering of a photon by molecules which are excited to higher energy levels. The effect was discovered in 1928 by C. V. Raman and his student K. S. Krishnan in liquids, and independently by Grigory Landsberg and Leonid Mandelstam in crystals. The effect had been predicted theoretically by Adolf Smekal in 1923.

See also

Related Research Articles

Buckminsterfullerene chemical compound

Buckminsterfullerene is a type of fullerene with the formula C60. It has a cage-like fused-ring structure (truncated icosahedron) that resembles a soccer ball (football), made of twenty hexagons and twelve pentagons, with a carbon atom at each vertex of each polygon and a bond along each polygon edge.

Raman spectroscopy spectroscopic technique used to observe vibrational, rotational, and other low-frequency modes in a system

Raman spectroscopy ; named after Indian physicist Sir C. V. Raman) is a spectroscopic technique used to observe vibrational, rotational, and other low-frequency modes in a system. Raman spectroscopy is commonly used in chemistry to provide a structural fingerprint by which molecules can be identified.

Fluorescein chemical compound

Fluorescein is a manufactured organic compound and dye. It is available as a dark orange/red powder slightly soluble in water and alcohol. It is widely used as a fluorescent tracer for many applications.

Fluorophore Agents that emit light after excitation by light. The wave length of the emitted light is usually longer than that of the incident light. Fluorochromes are substances that cause fluorescence in other substances, i.e., dyes used to mark or label othe

A fluorophore is a fluorescent chemical compound that can re-emit light upon light excitation. Fluorophores typically contain several combined aromatic groups, or planar or cyclic molecules with several π bonds.

<i>beta</i>-Carotene chemical compound

β-Carotene is an organic, strongly colored red-orange pigment abundant in plants and fruits. It is a member of the carotenes, which are terpenoids (isoprenoids), synthesized biochemically from eight isoprene units and thus having 40 carbons. Among the carotenes, β-carotene is distinguished by having beta-rings at both ends of the molecule. β-Carotene is biosynthesized from geranylgeranyl pyrophosphate.

Pyrene chemical compound

Pyrene is a polycyclic aromatic hydrocarbon (PAH) consisting of four fused benzene rings, resulting in a flat aromatic system. The chemical formula is C
16H
10. This colorless solid is the smallest peri-fused PAH. Pyrene forms during incomplete combustion of organic compounds.

Two-photon excitation microscopy

Two-photon excitation microscopy is a fluorescence imaging technique that allows imaging of living tissue up to about one millimeter in depth. It differs from traditional fluorescence microscopy, in which the excitation wavelength is shorter than the emission wavelength, as the wavelengths of the two exciting photons are longer than the wavelength of the resulting emitted light. Two-photon excitation microscopy typically uses near-infrared excitation light which can also excite fluorescent dyes. However, for each excitation, two photons of infrared light are absorbed. Using infrared light minimizes scattering in the tissue. Due to the multiphoton absorption, the background signal is strongly suppressed. Both effects lead to an increased penetration depth for these microscopes. Two-photon excitation can be a superior alternative to confocal microscopy due to its deeper tissue penetration, efficient light detection, and reduced photobleaching.

Perylene chemical compound

Perylene or perilene is a polycyclic aromatic hydrocarbon with the chemical formula C20H12, occurring as a brown solid. It or its derivatives may be carcinogenic, and it is considered to be a hazardous pollutant. In cell membrane cytochemistry, perylene is used as a fluorescent lipid probe. It is the parent compound of a class of rylene dyes.

Texas Red chemical compound

Texas Red or sulforhodamine 101 acid chloride is a red fluorescent dye, used in histology for staining cell specimens, for sorting cells with fluorescent-activated cell sorting machines, in fluorescence microscopy applications, and in immunohistochemistry. Texas Red fluoresces at about 615 nm, and the peak of its absorption spectrum is at 589 nm. The powder is dark purple. Solutions can be excited by a dye laser tuned to 595-605 nm, or less efficiently a krypton laser at 567 nm. The absorption extinction coefficient at 596 nm is about 85,000 M−1cm−1.

Quenching (fluorescence)

Quenching refers to any process which decreases the fluorescence intensity of a given substance. A variety of processes can result in quenching, such as excited state reactions, energy transfer, complex-formation and collisional quenching. As a consequence, quenching is often heavily dependent on pressure and temperature. Molecular oxygen, iodide ions and acrylamide are common chemical quenchers. The chloride ion is a well known quencher for quinine fluorescence. Quenching poses a problem for non-instant spectroscopic methods, such as laser-induced fluorescence.

Solvatochromism

Solvatochromism is the term used to describe the phenomenon that is observed when the colour due to a solute is different when that solute is dissolved in different solvents.

Fluorene chemical compound

Fluorene, or 9H-fluorene, is a polycyclic aromatic hydrocarbon. It forms white crystals that exhibit a characteristic, aromatic odor similar to that of naphthalene. It is combustible. It has a violet fluorescence, hence its name. For commercial purposes it is obtained from coal tar. It is insoluble in water and soluble in many organic solvents.

Molecular logic gate molecule that performs a logical operation

A molecular logic gate is a molecule that performs a logical operation based on one or more physical or chemical inputs and a single output. The field has advanced from simple logic systems based on a single chemical or physical input to molecules capable of combinatorial and sequential operations such as arithmetic operations i.e. moleculators and memory storage algorithms.

Tetraphenylporphyrin chemical compound

Tetraphenylporphyrin, abbreviated TPP or H2TPP, is a synthetic heterocyclic compound that resembles naturally occurring porphyrins. Porphyrins are dyes and cofactors found in hemoglobin and cytochromes and are related to chlorophyll and vitamin B12. The study of naturally occurring porphyrins is complicated by their low symmetry and the presence of polar substituents. Tetraphenylporphyrin is hydrophobic, symmetrically substituted, and easily synthesized. The compound is a dark purple solid that dissolves in nonpolar organic solvents such as chloroform and benzene.

J-aggregate

A J-aggregate is a type of dye with an absorption band that shifts to a longer wavelength of increasing sharpness when it aggregates under the influence of a solvent or additive or concentration as a result of supramolecular self-organisation. The dye can be characterized further by a small Stokes shift with a narrow band. The J in J-aggregate refers to E.E. Jelley who discovered the phenomenon in 1936. The dye is also called a Scheibe aggregate after G. Scheibe who also independently published on this topic in 1937.

Carbon quantum dots

Carbon quantum dots are small carbon nanoparticles with some form of surface passivation.

Cycloparaphenylene

Cycloparaphenylenes (CPPs) are cylindrical molecules made of para-linked benzene rings in a hoop-like structure. For this reason they are sometimes referred to as carbon nanohoops, especially because they can be viewed as a fragment of an armchair carbon nanotube (CNT). CPPs represent a challenging target to synthetic chemists due to the ring strain incurred from forcing benzene rings out of planarity.

References

  1. ↑ Sprenger, H. E. & Ziegenbein, W. (1966). "Condensation Products of Squaric Acid and Tertiary Aromatic Amines". Angew. Chem. Int. Ed. 5: 894. doi:10.1002/anie.196608941.
  2. ↑ E. Terpetschnig & J.R. Lakowicz (1993). "Synthesis and characterization of asymmetrical squarains – a novel class of cyanine dyes". Dyes and Pigments. 21: 227–234. doi:10.1016/0143-7208(93)85016-S.
  3. ↑ E. Terpetschnig; et al. (1993). "An investigation of squaraines as a new class of fluorophores with long-wavelength excitation and emission". Journal of Fluorescence. 3: 153. doi:10.1007/BF00862734.
  4. ↑ squarylium dye
  5. ↑ D. Keil; et al. (1991). "Synthesis and characterization of 1,3-bis-(2-dialkylamino-5-thienyl)-substituted squaraines—a novel class of intensively coloured panchromatic dyes". Dyes and Pigments. 17: 19. doi:10.1016/0143-7208(91)85025-4.
  6. ↑ K.-Y. Law (1987). "Squaraine chemistry. Effects of structural changes on the absorption and multiple fluorescence emission of bis[4-(dimethylamino) phenyl]squaraine and its derivatives". J. Phys. Chem. 91: 5184–5193. doi:10.1021/j100304a012.
  7. ↑ K. Yanagi; et al. (2007). "Photosensitive Function of Encapsulated Dye in Carbon Nanotubes". J. Am. Chem. Soc. 129 (16): 4992–4997. doi:10.1021/ja067351j. PMID   17402730.
  8. ↑ Y. Saito; et al. (2006). "Vibrational Analysis of Organic Molecules Encapsulated in Carbon Nanotubes by Tip-Enhanced Raman Spectroscopy". Jap. J. Appl. Phys. 45 (12): 9286–9289. Bibcode:2006JaJAP..45.9286S. doi:10.1143/JJAP.45.9286.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.