Names | |
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IUPAC name 1-methyl-4-[(oxocyclohexadienylidene)ethylidene]-1,4-dihydropyridine | |
Identifiers | |
3D model (JSmol) | |
ChemSpider | |
ECHA InfoCard | 100.255.640 |
PubChem CID | |
UNII | |
CompTox Dashboard (EPA) | |
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Properties | |
C14H13NO | |
Molar mass | 211.26 g/mol |
Appearance | Red crystals |
Melting point | 220 °C (428 °F; 493 K) (decomposes) |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). |
Brooker's merocyanine (1-methyl-4-[(oxocyclohexadienylidene)ethylidene]-1,4-dihydropyridine, MOED) [1] is an organic dye belonging to the class of merocyanines.
MOED is notable for its solvatochromic properties, meaning it changes color depending on the solvent in which it is dissolved.
As shown in the structural formula, MOED can be depicted using two resonance structures: neutral and zwitterionic. Research indicates that the zwitterionic structure is the major contributor to resonance hybrid when the compound exists in polar solvents such as water, and the neutral form when it exists in nonpolar solvents such as chloroform. [2]
When MOED is dissolved in various liquids, its colour will vary, depending on the solvent and its polarity. In general, the more polar the solvent, the shorter the wavelengths of the light absorbed will be, this is referred to as a hypsochromic shift. When light of a certain colour (wavelength) is absorbed, the solution will appear in the complementary colour of the one absorbed. Therefore, in water, a highly polar solvent, MOED appears yellow (corresponding to absorbed blue light of wavelengths 435–480 nm), but is purple or blue (corresponding to absorbed green to yellow light of wavelengths 560–595 nm) in acetone, a less polar solvent.
The effect stems in part from the stabilization of the ground state of the merocyanine molecule in polar solvents, which increases the energy gap between the ground state and excited states, which corresponds to shorter wavelengths (increased energy) of the absorbed light. Similarly, protic and aprotic solvents also affect MOED in solution differently. Solvents that are hydrogen donors (i.e. water, acids), will affect the visible absorption spectra by engaging in hydrogen bonding or donating the hydrogen outright, making the molecule favor the zwitterionic resonance form; an example of this may be seen in the picture where acetic acid, though less polar than water, was able to produce a more yellow solution.
Solvent | Color | λ(max, nm) | Relative solvent polarity [4] |
---|---|---|---|
Water | Yellow | 442 | 1 |
Methanol | Red-orange | 509 | 0.762 |
Ethanol | Red | 510 | 0.654 |
2-Propanol | Violet | 545 | 0.546 |
DMSO | Blue-violet | 572 | 0.444 |
Acetone | Blue-violet | 577 | 0.355 |
Pyridine | Blue | 603 | 0.302 |
Chloroform | Blue | 618 [5] | 0.259 |
Because of its solvatochromic properties MOED, and solvatochromic dyes in general, are useful as solvent polarity indicators, and for creating solutions that absorb light at a specific frequency. Additional potential areas of use include pH sensors and transition metal cation indicators. Further uses of MOED includes the production of certain photosensitive materials. Research into merocyanine dyes is ongoing. [6]
Brooker's merocyanine can be prepared beginning with the methylation of 4-methylpyridine to produce 1,4-dimethylpyridinium iodide. Base catalyzed reaction with 4-hydroxybenzaldehyde and subsequent intramolecular dehydration provides Brooker's merocyanine.
A solvent is a substance that dissolves a solute, resulting in a solution. A solvent is usually a liquid but can also be a solid, a gas, or a supercritical fluid. Water is a solvent for polar molecules and the most common solvent used by living things; all the ions and proteins in a cell are dissolved in water within the cell.
Solvation describes the interaction of a solvent with dissolved molecules. Both ionized and uncharged molecules interact strongly with a solvent, and the strength and nature of this interaction influence many properties of the solute, including solubility, reactivity, and color, as well as influencing the properties of the solvent such as its viscosity and density. If the attractive forces between the solvent and solute particles are greater than the attractive forces holding the solute particles together, the solvent particles pull the solute particles apart and surround them. The surrounded solute particles then move away from the solid solute and out into the solution. Ions are surrounded by a concentric shell of solvent. Solvation is the process of reorganizing solvent and solute molecules into solvation complexes and involves bond formation, hydrogen bonding, and van der Waals forces. Solvation of a solute by water is called hydration.
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In organometallic chemistry, organolithium reagents are chemical compounds that contain carbon–lithium (C–Li) bonds. These reagents are important in organic synthesis, and are frequently used to transfer the organic group or the lithium atom to the substrates in synthetic steps, through nucleophilic addition or simple deprotonation. Organolithium reagents are used in industry as an initiator for anionic polymerization, which leads to the production of various elastomers. They have also been applied in asymmetric synthesis in the pharmaceutical industry. Due to the large difference in electronegativity between the carbon atom and the lithium atom, the C−Li bond is highly ionic. Owing to the polar nature of the C−Li bond, organolithium reagents are good nucleophiles and strong bases. For laboratory organic synthesis, many organolithium reagents are commercially available in solution form. These reagents are highly reactive, and are sometimes pyrophoric.
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.
Photochromism is the reversible transformation of a chemical species (photoswitch) between two forms by the absorption of electromagnetic radiation (photoisomerization), where the two forms have different absorption spectra. In plain language, this can be described as a reversible change of color upon exposure to light.
In chemistry, solvatochromism is the phenomenon observed when the colour of a solution is different when the solute is dissolved in different solvents.
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5H
4NH(O). It is a colourless solid. It is well known to form hydrogen bonded dimers and it is also a classic case of a compound that exists as tautomers.
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Fluorescence is used in the life sciences generally as a non-destructive way of tracking or analysing biological molecules. Some proteins or small molecules in cells are naturally fluorescent, which is called intrinsic fluorescence or autofluorescence. Alternatively, specific or general proteins, nucleic acids, lipids or small molecules can be "labelled" with an extrinsic fluorophore, a fluorescent dye which can be a small molecule, protein or quantum dot. Several techniques exist to exploit additional properties of fluorophores, such as fluorescence resonance energy transfer, where the energy is passed non-radiatively to a particular neighbouring dye, allowing proximity or protein activation to be detected; another is the change in properties, such as intensity, of certain dyes depending on their environment allowing their use in structural studies.
In chemistry, solvent effects are the influence of a solvent on chemical reactivity or molecular associations. Solvents can have an effect on solubility, stability and reaction rates and choosing the appropriate solvent allows for thermodynamic and kinetic control over a chemical reaction.
In organic chemistry, enone–alkene cycloadditions are a version of the [2+2] cycloaddition This reaction involves an enone and alkene as substrates. Although the concerted photochemical [2+2] cycloaddition is allowed, the reaction between enones and alkenes is stepwise and involves discrete diradical intermediates.
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Structural of methine dyes
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