Dipyrromethene Dyes

Dipyrromethene dye is a kind of visible region dye, which has many excellent optical properties. Firstly, the dye has strong absorption in the ultraviolet region. Secondly, the fluorescence spectrum wavelength of the dye can be adjusted, up to more than 600nm. Thirdly, the half-peak width in fluorescence spectrum of the dye is narrow. Finally, the fluorescence quantum yield of the dye is high. In the parent structure of dipyrromethene dye molecule, boron nitride heterocyclic ring in the middle and pyrrole ring on the left and right sides constitute a rigid planar conjugated structure, and two fluorine atoms are located on both sides of the plane. The R1-R8 positions in the molecular structure can be modified, and different functional groups can be introduced into different positions to obtain derivatives with different properties. Therefore, by selectively introducing functional groups, the optical properties, chemical properties and physical properties can be adjusted.

Figure 1. The parent structure of dipyrromethene dye molecule.

Applications:

• Photodynamic therapy field: Dipyrromethene dyes can be used as photosensitizers in photodynamic therapy. Based on photosensitizer and light that has corresponding wavelength to the absorption spectrum of such photosensitizer, photodynamic therapy is a non-invasive treatment for cancer. When the photosensitizer is injected into the organism and metabolized for a period of time, the concentration of photosensitizer in the tumor tissues is higher than that in normal tissues. At this time, if the laser of the corresponding wavelength is irradiated to the affected area, the tumor tissues can be destroyed. As photosensitizers of photodynamic therapy, dipyrromethene dyes have high selectivity for cancer treatment. In areas not exposed to light, photosensitizers are non-toxic, and  tend to be toxic when exposed to light.

Figure 2. Dipyrromethene dye used in photodynamic therapy.

• Fluorescent sensors field: Fluorescent sensors are molecules that can effectively express molecular recognition events through fluorescent signals. A typical fluorescent sensor is generally composed of fluorophore, spacer and acceptor. The response to molecular recognition process is achieved through "on-off" fluorescence.

Figure 3. Dipyrromethene dye applied as a fluorescent sensor.

• Fluorescent probe field: Fluorescent probe uses fluorescent reagent to label or generate covalent or non-covalent derivatives with high fluorescence intensity. This detection method has the advantages of high sensitivity and low detection limit, and can be used to detect metal ions, organic molecules and biomacromolecules. In particular, the modified NIR dipyrromethene dyes have great potential application prospect in the field of biological detection due to their small damage to organisms.

Figure 4. Dipyrromethene dye designed as a fluorescent probe.

• The others: The dipyrromethene dyes are also widely used in other fields, such as tunable lasers, and solar cells.

Classification:

According to the solubility of dipyrromethene dyes, it can be divided into water-soluble, amphiphilic and water-insoluble dipyrromethene dyes.

• Water-soluble dipyrromethene dyes: Water-soluble dipyrromethene dyes refer that the dyes have good solubility in aqueous media.
• Amphiphilic dipyrromethene dyes: Amphiphilic dipyrromethene dyes mean that the dyes have certain solubility in both the aqueous and the oil phases.
• Water-insoluble dipyrromethene dyes: Water-insoluble dipyrromethene dyes refer that the dyes have good solubility in oil phases.

References:

1. Awuah S G, You Y. Boron dipyrromethene (BODIPY)-based photosensitizers for photodynamic therapy[J]. Rsc Advances, 2012, 2(30):11169-11183.
2. Wu Y, Peng X, Guo B, et al. Boron dipyrromethene fluorophore based fluorescence sensor for the selective imaging of Zn(II) in living cells[J]. Organic & Biomolecular Chemistry, 2005, 3(8):1387-1392.
3. Rational design of a boron-dipyrromethene-based fluorescent probe for detecting Pd²⁺ sensitively and selectively in aqueous media[J]. Analyst, 2019, 144.