**2. Rational design of photoactive graphene**

Graphene can be functionalized at the basal plane and the edges.[32] On the basal plane, sp2 hybridization of carbon leads to a strong covalent bonding, as well as delocalization of the π electrons. The sheet edges are considered the most reactive sites,[33] and the dangling bonds at edge sites of graphene are highly reactive to guest atoms or molecules. In addition, the functional molecules attached onto the basal plane of graphene lead to modification of the π– π conjugation and thus the physical and chemical properties and the electron density distri‐ bution. There are generally three major purposes for chemically functionalizing graphene: enabling its solution processing, tuning its energy level and gap, as well as providing photo‐ active functionalities.[8]
