**1.1. What is photoactive graphene?**

The term "photoactive graphene" generally refers to graphene that undergo a chemical or physical reaction when interacted with sunlight and/or ultraviolet light. Unlike the transparent pristine graphene, photoactive graphene shows optical response characteristics when light passes through it.

To date, two different approaches toward the preparation of photoactive graphene can be found in the literature. As shown in Figure 1 (a), the first is based on the bandgap engineering (opening and tuning) of pristine graphene,[7] and in the second strategy the photoactive graphene is obtained by chemical functionalization with photoactive moieties.[8] The most reported examples of the first route are roughly classified into four categories: (1) heteroatom doping;[9-11] (2) chemical modification;[12] (3) electrostatic field tuning;[13, 14] and (4) cutting graphene into nanoribbons.[15-19] As shown in Figure 1 (b), the second strategy for giving photoactive to graphene is chemical functionalization of graphene with photoactive units, including organic conjugated molecules and polymers, inorganic semiconductors particles and quantum dots, rare-earth metal complexes, and so on. This approach has been demon‐ strated to be a feasible route to achieve the photo-electron response of graphene to light.[8, 20] Herein, we will only discuss the progress and challenges related to the chemical function‐ alization approach to preparing photoactive graphene.

**Figure 1.** Two different approaches toward the photoactive graphene. One is based on the bandgap opening and tun‐ ing of pristine graphene (a), another strategy is chemical functionalization of graphene with photoactive moieties (b).
