Fluorescent Dyes

What are cyanine dyes?

Cyanine dyes are a class of dyes that can increase the photosensitivity of photosensitive materials. In 1873, it was discovered that the addition of cyanine dyes to silver bromide emulsions can make the emulsions produce new photosensitivity in the spectral region absorbed by the dyes. Since then, cyanine dyes have been widely used in black and white film, color film and infrared film. . Cyanine dyes are also often referred to as spectral sensitizers or sensitizing dyes.

basic structure
The basic structure of cyanine dyes can be represented by hybrid resonances of the following two limiting formulas:
Two nitrogen atoms are part of a heterocyclic nucleus, and the nitrogen atoms are connected by a chain of multiple methine groups. There are various heterocyclic rings, such as quinoline, thiazole and the corresponding benzo system. If the two ends of the above-mentioned chromophore conjugated system are established between nitrogen and oxygen atoms, such dyes are called merocyanines, also called neutral cyanines.
There are many types of dyes, which can be divided into cyanine, merocyanine and polynuclear cyanine according to the different chromophore conjugated systems; thiocarbocyanine, oxycarbocyanine and imidcarbocyanine according to the type of heterocyclic nucleus contained; According to the length of the polymethyl chain, it can be divided into primary methyl cyanine, secondary methyl cyanine (carbocyanine), pentamethine cyanine (dicarbocyanine), hepta methine cyanine (tricarbocyanine) and the like. Important cyanine dye varieties are as follows.

Cyanine dyes for black and white film
For example, the sensitizing dye N1555 is a sensitizing dye for black and white film, and its structural formula is:
λ=505nm
S=555nm (sensitization range 510~580nm)
λmax is the maximum absorption wavelength, and Smax is the maximum sensitization wavelength.

main application
Cyanine dyes used in color films such as:
①The sensitizing dye Rr340 is a sensitizing dye for color positive and negative films, and its structural formula is:
②The sensitizing dye Rr1833 is a sensitizing dye for the red-sensitive layer of the color positive film, and its structural formula is: sensitizing dye for infrared film, such as: cyanine dyes adsorbed on the surface of silver bromide crystals, sometimes reducing the sensitivity of silver bromide to blue light , called desensitization. Desensitizing dyes usually have this property, but some dyes have a significant desensitization effect, and some have no significant desensitization effect. Commonly used attenuating dyes such as α, β-azocarbocyanine.

Cyanine dyes
Cyanine dyes are a kind of nucleic acid dyes, which have the advantages of large molar absorption coefficient and high fluorescence quantum yield. By adjusting the length of the conjugated chain, the spectrum of cyanine can extend from the visible light region to the near-infrared region. Using the red region measurement can effectively eliminate background interference and obtain more ideal analytical sensitivity and selectivity. The spectrum of cyanine dyes is extremely sensitive to changes in the external microenvironment, which is very suitable for the analysis and research of biological and environmental samples.

Polymethine dye
Polymethyl cyanine dyes are a kind of chemicals. Various heterocycles such as indole, pyridine, quinoline, thiazole, and pyrrole are often used as end groups in cyanine dyes. The reflectivity and stability are better than other cyanine dyes.