cyanine dyes

https://doi.org/10.1351/goldbook.C01487
Synthetic dyes with the general formula R2N[CH=CH]nCH=N+R2mesomer-arrow chemimgR2N+=CH[CH=CH]nNR2 (n is a small number) in which the nitrogen and part of the conjugated chain usually form part of a heterocyclic system, such as imidazole, pyridine, pyrrole, quinoline and thiazole, e.g.
C01487.png
Source:
PAC, 1995, 67, 1307. (Glossary of class names of organic compounds and reactivity intermediates based on structure (IUPAC Recommendations 1995)) on page 1329 [Terms] [Paper]