J-aggregate
Encyclopedia
A J-aggregate is a type of dye
with an absorption band
that shifts to a longer wavelength
(bathochromic shift
) of increasing sharpness (higher absorption coefficient) 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 .
Scheibe and Jelley independently observed that in ethanol
the dye PIC chloride has two broad absorption maxima at around 19,000 cm-1 and 20,500 cm-1 and that in water a third sharp absorption maximum appears at 17,500 cm-1 (571 nm). The intensity of this band further increases on increasing concentration
and on adding sodium chloride
. In the oldest aggregation model for PIC chloride the individual molecules are stacked like a roll of coins forming a supramolecular polymer but the true nature of this aggregation phenomenon is still under investigation. Analysis is complicated because PIC chloride is not a planar molecule. The molecular axis can tilt in the stack creating a helix pattern. In other models the dye molecules orientate themselves in a bickwork, ladder or staircase fashion. In various experiments the J-band was found to split as a function of temperature, liquid crystal
phases were found with concentrated solutions and CryoTEM revealed aggregeate rods 350 nm long and 2.3 nm in diameter.
J-aggregate dyes are found with polymethine
dyes in general, with cyanine
s, merocyanine
s, squaraine and perylene bisimides.
In H-aggregates a hypsochromic shift
is observed with low or no fluorescence
.
Dye
A dye is a colored substance that has an affinity to the substrate to which it is being applied. The dye is generally applied in an aqueous solution, and requires a mordant to improve the fastness of the dye on the fiber....
with an absorption band
Absorption band
An absorption band is a range of wavelengths, frequencies or energies in the electromagnetic spectrum which are able to excite a particular transition in a substance...
that shifts to a longer wavelength
Wavelength
In physics, the wavelength of a sinusoidal wave is the spatial period of the wave—the distance over which the wave's shape repeats.It is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings, and is a...
(bathochromic shift
Bathochromic shift
Bathochromic shift is a change of spectral band position in the absorption, reflectance, transmittance, or emission spectrum of a molecule to a longer wavelength ....
) of increasing sharpness (higher absorption coefficient) 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
Stokes shift
Stokes shift is the difference between positions of the band maxima of the absorption and emission spectra of the same electronic transition. It is named after Irish physicist George G. Stokes. When a system absorbs a photon, it gains energy and enters an excited state...
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 .
Scheibe and Jelley independently observed that in ethanol
Ethanol
Ethanol, also called ethyl alcohol, pure alcohol, grain alcohol, or drinking alcohol, is a volatile, flammable, colorless liquid. It is a psychoactive drug and one of the oldest recreational drugs. Best known as the type of alcohol found in alcoholic beverages, it is also used in thermometers, as a...
the dye PIC chloride has two broad absorption maxima at around 19,000 cm-1 and 20,500 cm-1 and that in water a third sharp absorption maximum appears at 17,500 cm-1 (571 nm). The intensity of this band further increases on increasing concentration
Concentration
In chemistry, concentration is defined as the abundance of a constituent divided by the total volume of a mixture. Four types can be distinguished: mass concentration, molar concentration, number concentration, and volume concentration...
and on adding sodium chloride
Sodium chloride
Sodium chloride, also known as salt, common salt, table salt or halite, is an inorganic compound with the formula NaCl. Sodium chloride is the salt most responsible for the salinity of the ocean and of the extracellular fluid of many multicellular organisms...
. In the oldest aggregation model for PIC chloride the individual molecules are stacked like a roll of coins forming a supramolecular polymer but the true nature of this aggregation phenomenon is still under investigation. Analysis is complicated because PIC chloride is not a planar molecule. The molecular axis can tilt in the stack creating a helix pattern. In other models the dye molecules orientate themselves in a bickwork, ladder or staircase fashion. In various experiments the J-band was found to split as a function of temperature, liquid crystal
Liquid crystal
Liquid crystals are a state of matter that have properties between those of a conventional liquid and those of a solid crystal. For instance, an LC may flow like a liquid, but its molecules may be oriented in a crystal-like way. There are many different types of LC phases, which can be...
phases were found with concentrated solutions and CryoTEM revealed aggregeate rods 350 nm long and 2.3 nm in diameter.
J-aggregate dyes are found with polymethine
Polymethine
Polymethines are compounds made up from an odd number of methine groups bound together by alternating single and double bonds.Compounds made up from an even number of methine groups are known as polyenes....
dyes in general, with cyanine
Cyanine
Cyanine is a non-systematic name of a synthetic dye family belonging to polymethine group. Cyanines have many uses as fluorescent dyes, particularly in biomedical imaging...
s, merocyanine
Merocyanine
Merocyanines are a class of fluorescent dyes typified by merocycanine I.These dyes are usually intensely colored and have large extinction coefficients....
s, squaraine and perylene bisimides.
In H-aggregates a hypsochromic shift
Hypsochromic shift
Hypsochromic shift is a change of spectral band position in the absorption, reflectance, transmittance, or emission spectrum of a molecule to a shorter wavelength...
is observed with low or no fluorescence
Fluorescence
Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation of a different wavelength. It is a form of luminescence. In most cases, emitted light has a longer wavelength, and therefore lower energy, than the absorbed radiation...
.