Photocatalyst is a general term for a chemical that can act as a catalyst when excited by photons. Photocatalysts through the absorption of visible light to reach the excited state to promote the reaction of high speed, greatly improve the utilization efficiency of light energy and has a high life, through the electron or energy transfer with the substrate, self-back to the ground state after reabsorption of visible light can continue to catalyze the reaction. In general, photocatalysis technology has used in environmental purification, advanced new energy, cancer medicine, efficient antibacterial and other cutting-edge fields.
Fig.1 Photocatalytic mechanism schematic diagram
The common photocatalyst can be divided into metal iridium, ruthenium complex photocatalyst, carbazole photocatalyst, acridine photocatalyst and so on according to its main structure.
- Iridium complexes: Iridium and other noble metal complexes and macromolecule conjugated substances can catalyze organic synthesis reactions under light induction. At present, such catalysts are mainly used in homogeneous catalytic reaction systems. Huang  used iridium polypyridine complex as photocatalyst and persulfate as precursor of HAT catalyst, the arylation of unactivated alkanes and heteraromatic hydrocarbons was successfully carried out under visible light irradiation. In addition, this reaction has good functional group tolerance and wide reaction range for alkanes and hetero-aromatic hydrocarbons substrates, and can directly obtain alkyl substituted N-hetero-aromatic hydrocarbons, which provides a convenient way for the synthesis of key structural elements in natural products and bioactive molecules.
Fig.2 The direct arylation of unactivated alkanes with heteroarenes 
- Ruthenium complexes: Ruthenium complexes play an increasingly important role in the field of photocatalysis due to their excellent photophysical and photochemical properties. When excited by light, it is used as the medium for electron transfer from electron donor sacrificial agent to catalyst in the reduction system, which involves two mechanisms: oxidation quenching and reduction quenching. In the photocatalytic oxidation system, as the medium to realize the hole transfer from electron acceptor sacrifice agent to catalyst, so as to achieve the photocatalytic effect. Peter  and his co-workers reported a new synthetic pathway, which uses ruthenium metal complex as photocatalyst, to obtain the oxazoline skeleton by regionally selective visible light induced cyclization, and to generate many multisubstituted oxazoline.
Fig.3 Synthetic route 
- Carbazole class: Conjugated polymer performance research is very extensive, in photoelectric, catalysis, lithium battery, gas adsorption, ultracapacitors, medicine and other aspects have a more comprehensive study. Carbazoles and their derivatives have good photocatalytic properties and energy storage properties as electron rich and hole transport materials, so carbazoles are widely concerned. For example, the relatively inexpensive organic photocatalyst 4CzIPN has the advantages of long excited state lifetime, wide REDOX window and high fluorescence quantum yield, so it is very attractive to apply it to metal-free organic photosynthesis .
Fig.4 Structure of 4CzIPN
- Acridine class: The high cost of noble metal photocatalyst promotes the development of small molecule organic dye photocatalyst. Acridine salt as an effective and sustainable choice of photocatalyst has attracted extensive attention. With the development of technology, the photophysical properties and stability of acridine photocatalyst were improved by modifying the core structure of acridine photocatalyst. In 2004, Fukuzumi [4,5] disclosed an organic photocatalyst, 9-mesityl-10-methylacridinium perchlorate, Mes-Acr-MeClO4, which has a reported excited-state reduction potential. Because of the highly positive reduction potential of this photocatalyst and the reported long-lived excited state, it may be considered to facilitate single electron oxidation of a variety of alkenes, including unactivated alkenes. Then, Kaila  designed a general approach to catalytic Alkene anti-Markovnikov hydrofunctionalization reactions via acridinium photoredox catalysis.
Fig.5 Synthetic route via acridinium photoredox catalysis
Alfa chemistry provides a variety of photocatalysts, including transition metal complexes of iridium and ruthenium, acridine photocatalysts, carbazole photocatalysts and other common photocatalysts. If you do not find the product you need in our catalogue, please contact us, we are pleased to provide you with exclusive custom service.
- Huang.; et al, Direct arylation of unactivated alkanes with heteroarenes by visible-light catalysis. The Journal of Organic Chemistry, 2019, 84(20): 12904-12912.
- Peter.; et al, Visible light-induce regioselective cycloaddition of benzoyl azides and alkenes to yield oxazolines. The Journal of Organic Chemistry, 2019, 84(10): 6278-6285.
- Lu, J.; et al, Donor–Acceptor Fluorophores for Energy-Transfer-Mediated Photocatalysis. J. Am. Chem. Soc. 2018, 140, 13719.
- Fukuzumi, S.; et al, Electron-Transfer State of 9-Mesityl-10-methylacridinium Ion with a Much Longer Lifetime and Higher Energy Than That of the Natural Photosynthetic Reaction Center. J. Am. Chem. Soc. 2004, 126, 1600−1601.
- Ohkubo, K.; et al, Simultaneous Production of p-Tolualdehyde and Hydrogen Peroxide in Photocatalytic Oxygenation of p-Xylene and Reduction of Oxygen with 9-Mesityl-10-Methylacridinium Ion Derivatives. Chem. Commun. 2010, 46, 601.
- Kaila A,; et al, A general approach to catalytic Alkene anti-Markovnikov hydrofunctionalization reactions via acridinium photoredox catalysis. Acc. Chem. Res, 2016, 49, 9, 1997–2006.