Introduction
The ketone photosensitizer is an important kind of photosensitizer and features many advantages, such as good structural planarity, simple synthesis and easy structure modification. With so many advantages, the ketone photosensitizer has been extensively applied to various fields, including dye-sensitized solar cell (DSSC), phototherapy and photosensitized reaction. The ketone photosensitizer also is an important structural unit in the field of organic optoelectronic materials and is sequentially used in function materials and organic photovoltaics.
Categories
According to the structure and properties of the ketone photosensitizer, the common ketone photosensitizers can be divided into the following categories.
- Flavonoid-based photosensitizers
The most important is flavonoid-based photosensitizers in the field of ketone photosensitizers. The flavonoid-based photosensitizers usually can be extracted from flowers petals, leaves, roots, and barks. Compared to the traditional metal complex sensitizers, flavonoid-based photosensitizers contain outstanding features, such as being environmentally-friendly, abundant, low cost, simple extraction process and so on.[1] Moreover, the flavonoid-based photosensitizers extracted from the red grape, radish, sour orange peel exhibit a favorable coupling with TiO2 by the hydroxyl and carbonyl groups. Also, the flavonoid-based photosensitizers extracted from the radish was extensively applied in DSSC to improve the DSSC performance. The structure of flavonoid-based photosensitizers was flexible which makes the design of new efficient DSSCs possible.
- Diketopyrrolopyrrole-based photosensitizers
Compared to the flavonoid-based photosensitizers, the diketopyrrolopyrrole-based (DPP) photosensitizers photosensitizers have two nitrogen atoms in the five-membered heterocycle. Given its good structural planarity, simple synthesis and easy structure modification, the DPP photosensitizers play an important part in phototherapy.[2] In addition, DPP photosensitizer also is an important structural unit in the field of organic optoelectronic materials because of their highly stable, strong electron affinity and high molar absorption coefficient. They are also widely used in various fields, such as fluorescent probes, biological imaging, organic sensitizing dyes and organic photovoltaics.
Figure 1. The DPP photosensitizers and its application
- Thioxanthones photosensitizers
The thioxanthones photosensitizer is a kind of famous Norrish type II photosensitizer that absorbs at 360-400 nm.[3] Thioxanthones photosensitizer was attractive as visible light photosensitizers when the long wave absorption combined with higher triplet energy. Due to their long wave absorption, the thioxanthones photosensitizer was added to different quaternary ammonium salts as latent active species and produce a series of photobase generators (PBGs). Meanwhile, PBGs were photosensitive to long wavelengths due to the characteristic absorption of thioxanthone at 380 nm. Importantly, a study on photolysis confirmed thioxanthone acetic acid is a highly efficient radical photoinitiator and the PBGs released active basic species efficiently to produce active free radicals.
Figure 2. The photosensitized reaction of thioxanthones photosensitizers
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References
- Sabagh S.; et al. Photovoltaic properties of the flavonoid-based photosensitizers: molecular-scale perspective on the natural dye solar cells. Int. J. Quantum Chem. 2020, 120(10): 26171-26182.
- Wang L.; et al. Research progress in cancer treatment by diketopyrrolopyrrole-based photosensitizers and photothermal agents. Chinese J. Org. Chem. 2020, 40(12): 4155-4167.
- Dong X.; et al. Thioxanthone acetic acid ammonium salts: highly efficient photobase generators based on photodecarboxylation. RSC Adv. 2015, 5(66): 53342-53348.
