Xanthene dyes refer to a class of dyes that have xanthene structure as the core. The fluorescence intensity of xanthene dyes is strong and the spectrum could range from yellow to red. Furthermore, the photophysical properties of xanthene dyes are also excellent, such as high molar extinction coefficient, high fluorescence quantum yield and high stability. Moreover, xanthene dyes could be easily modified. Therefore, those dyes have been widely used in various fields.
Figure 1. The molecular structure of xanthene dyes.
- Fluorescent probe: Fluorescent probe has the advantages of high sensitivity and strong selectivity, which are important for detection. Chromophore is one of the most important structures of fluorescent probes. Due to the high molar extinction coefficient, long excitation and emission wavelength, high fluorescence quantum yield and good water solubility, xanthene dyes are ideal candidates. Generally, a lactam or lactone structure segment is attached to the xanthene, and open-ring or closed-ring reaction occurs under the induction of the detected groups. Therefore, the conjugated system of xanthene chromophore is changed, causing the fluorescence of the fluorescent probe to be “on” or “off”.
Figure 2. The detection mechanism of xanthene fluorescent probe.
- Photocatalyst field: Visible light is a cheap, readily available, and renewable resource. Taking the advantages of mild reaction conditions and simple operation, visible light-induced reactions have received widespread attention. Xanthene dyes contain large π conjugated system, which can realize π-π* transition under the irritation of low-energy visible light, making it an important visible light catalyst. As a photocatalyst, xanthene dye can be applied in many reactions, including cross-coupling reactions, cyclization, oxidation reaction, reduction reaction, etc.
- Dyeing field: With high stability, xanthene dyes can be used as colorants for dyeing various fabrics, cosmetics, crayons and inks. Moreover, xanthene dyes are often used as markers to stain cells and tissues, which can be observed and detected by fluorescence microscope or flow cytometer.
- The others: Xanthene dyes can be used to study the speed and direction of water flow due to their bright color and water solubility. In addition, xanthene dyes can also be used as anti-bacterial, anti-viral and anti-inflammatory drugs.
Classification: Xanthene dyes can be divided in to fluorescein, rhodamine and rhodol.
- Fluorescein: Fluorescein was firstly synthesized by von Baeyer in 1871. Fluorescein is soluble in many solvents, such as acetone, methanol and the others, and can be used as an indicator in chemical analysis, biological detection and the others.
Figure 3. The molecular structure of fluorescein.
- Rhodamine: Rhodamine was firstly reported by Noelting and Dziewoński in 1905. The water solubility of rhodamine is excellent, and can be used in fluorescent cell stain, colored glass and other industries. Unfortunately, rhodamine is carcinogenic, so it is no longer allowed to be used as a food stain.
Figure 4. The molecular structure of Rhodamine dye.
- Rhodol dyes: Rhodol is a hybrid of fluorescein and rhodamine.
Figure 5. The molecular structure of Rhodol dyes.
- Baeyer A. Uber Ein Neue Klasses von Farbstoffen (On a New Class of Dyes) [J].Ber Dtsch Chem Ges, 1871, 4:555-558.
- Noelting, Dziewobski K. Zur Kenntniss der Rhodamine [J].Ber Dtsch Chem Ges,1905,38:3516-3527.