Cyanines

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Cyanine ( Gr. Cyanos , κυανός, blue ) or cyanine dyes is a collective name for synthetic, organic dyes from the group of polymethine dyes. These were systematized by Walter König in 1922 . All cyanines have both a quaternary ammonium group as an electron acceptor ( antiauxochrome ) and a tertiary amino group as an electron donor ( auxochrome ), which are linked by a polyene bridge. Cyanines are therefore always imines ( azomethines ). Both groups have a relatively strong bathochromic effect , which is why cyanine dyes even with very small π-electron systems absorb light in the visible range.

The group of cyanine dyes includes the diarylmethane dyes , the triphenylmethane dyes and the dyes of the quinonimines .

structure

The three subgroups of cyanines:
I = open-chain or streptocyanines,
II = hemicyanines,
III = closed -chain cyanines

The cyanines are divided into three subgroups:

  • The structure of the streptocyanine or open chain cyanine is
R 2 N + = CH [CH = CH-] n NR 2 (I)
  • If the quaternary nitrogen atom is part of a heterocyclic ring system, it is referred to as hemicyanine :
Aryl = N + = CH [CH = CH-] n NR 2 (II)
  • If the second nitrogen atom is also part of a ring, it is a closed-chain cyanine :
Aryl = N + = CH [CH = CH-] n N = Aryl (III)

The chain links between the two nitrogen atoms are usually in the more stable all-trans form . In many cases, derivatives of nitrogen-containing heterocycles such as quinolines , thiazoles , pyrroles , imidazoles or oxazoles in which one or both nitrogen atoms are part of a ring system are also used. The heterocyclic dye compound can thus either be a hemicyanine (type II) or a closed-chain cyanine (type III).

Manufacturing

Cyanine dyes can be made using a variety of methods, including the condensation of complex aldehydes with amines .

Common cyanine dyes

dye Excitation wavelength (nm) Emission wavelength (nm) Molar mass in g mol −1 Photon yield
Cy2 489 506 714 0.12
Cy3 (512); 550 570; (615) 767 0.15
Cy3B 558 572; (620) 658 0.67
Cy3.5 581 594; (640) 1102 0.15
Cy5 (625); 649 670 792 0.28
Cy5.5 675 694 1128 0.28
Cy7 743 767 818 0.28

Properties and use

Most cyanines are colored blue and sensitive to light, so they have poor color fastness and are generally unsuitable for dyeing textiles. The photosensitivity makes them ideal for use in photography , where they are used to sensitize the photo emulsion . Cyanines are also used in organic dye lasers and as a medicine against worm infections . Brooker's merocyanine is used as a solvatochromic indicator .

CD / DVD dye

Cyanines were used for the production of the first CD-Rs and are partly still in use (e.g. by Taiyo Yuden), as specified in the Orange Book . Since cyanine is chemically unstable, various mixtures (metal-stabilized cyanine from TDK , Super Cyanine from Taiyo Yuden ) have been developed that have the same durability as the azo and phthalocyanine media. Cyanine dyes for CD-R are patented by Taiyo Yuden. Like azo dyes, cyanines are long-strategy dyes . Type numbers 0 to 4 are reserved for cyanines on CD-R. Today's DVD-R media use mixtures of cyanines and azo dyes.

biochemistry

After SDS-PAGE , proteins can be stained with the triaryl methane dye Coomassie brilliant blue or the merocyanines Fast Green FCF , SYPRO Orange or SYPRO Red . The asymmetric cyanine dye SYBR Green I is used to detect double-stranded DNA . The triarylmethane dyes fuchsin and parafuchsin are used for staining in histology . Various cyanines can be used for molecular marker used for. B. Cy5 succinimidyl ester .

See also

Individual evidence

  1. ↑ Johannes, HH: Cyanine: Direct functionalization, oligomerization, linear and non-linear optical properties , dissertation TU Braunschweig , 2000.
  2. ↑ a b Entry on cyanine dyes. In: Römpp Online . Georg Thieme Verlag, accessed on August 14, 2013.
  3. ↑ K, Umezawa, A, Matsui, Y, Nakamura, D, Citterio, K, Suzuke: Bright, Color-Tunable Fluorescent Dyes in the Vis / NIR Region: Establishment of New “Tailor-Made” Multicolor Fluorophores Based on Borondipyrromethene . In: Chem Eur J.. . 15, 2009, p. 1096. doi : 10.1002 / chem.200801906 .
  4. ↑ Shelf life comparison: cyanine and metal-stabilized cyanine
  5. ↑ OJ Keray: Functionalized cyanine dyes as molecular labeling reagents (PDF; 3.3 MB) , dissertation at Heinrich Heine University Düsseldorf , 2007.