**2. Photocatalysts**

Photocatalysts are organic or inorganic substances that absorb light and get excited to a higher energy level and transfer this energy to a reacting partner thereby triggering a chemical reaction. Few commonly used photocatalysts for the difunctionalization of alkenes [6] are shown in (**Figures 2** and **3**). These photocatalysts can be divided into two categories: (A) Transition-metal complexes and (B) Organic dyes.


**Figure 2.** *Commonly used metal-based Photocatalyst for Difunctionalization.*

*Construction of C-N Bond* via *Visible-Light-Mediated Difunctionalization of Alkenes DOI: http://dx.doi.org/10.5772/intechopen.98949*

#### **Figure 3.**

*Commonly used organic dye Photocatalyst for Difunctionalization of alkene.*

in the formations of carbon-heteroatom bond in the difunctionalization of alkene. Compared to metal-containing photocatalyst, organic dyes require mild reaction conditions as it uses visible light of low power source and therefore the number of organic dyes have been employed as photo redox catalysts [8].

### **3. General mechanism**

In general, at first, a photocatalyst (P.C) is converted to its excited state (\*P.C) by irradiation of visible light and undergoes an energy transfer or a redox path. In the reductive quench path, the (\*P.C) absorbs an electron from the electron donor to produce a reduced photo catalyst (P.C). Which is a good reductant for the oneelectron reduction of the substrate (S) or transition metal (Mn+). Simultaneously, the photocatalyst is regenerate to the ground state and the reduced species radical anion (S**.** ) or M(n1)+ undergo further reaction. In the oxidative quench pathway, the (\*P.C) loses an electron to the electron acceptor to generate an oxidized photo catalyst (P.C<sup>+</sup> ) which is a good oxidant for the one-electron oxidation of the substrate (S) or transition metal (Mn+). The photo catalyst is regenerated and oxidative species radical cation (S+**.** ) or M(n + 1) + could undergo further transformations. Both of these cycles produce D <sup>+</sup>• and A • radicals in a single operation through SET to

**Figure 4.** *Redox Photocatalyst via reductive or oxidative pathway.*

make the overall process neutral. Here, the reductive path refers to the reduction of the excited photo catalyst (\*P.C) where the external electron donor D is oxidized, whereas the oxidative path defines oxidation of the excited photo catalyst (\*P.C) with concomitant reduction of the external electron acceptor A (**Figure 4**).
