**4.2. Photocatalysts**

their study on employing ethidium bromide (EB) as a model for constructing an inexpen‐ sive and label-free biosensor to improve the sensitivity performance of GO–DNA-based sensors. Experiment results indicated that the fluorescence of EB was quenched by GO in

**Figure 6.** Nonradiative decay by dipolar coupling to electron–hole pair transition in the graphene surface and to a low‐

Covalent or noncovalent functionalization of graphene with various photoactive compo‐ nents has been considered to be crucial for graphene processing.[44, 45] The photoactive graphene *via* chemical approach holds promise for optimizing dispersibility in common solvents, tailoring surface chemical reactivity, and tuning the electronic properties of graphene.[43] Therefore, chemical functionalization strategy produced photoactive gra‐ phene has many advantages over pristine graphene and bare photoactive molecules, especially in the field of photo-energy conversion devices and as synergistic catalyst for

A typical OPV cell consists of a transparent conductor, a photoactive layer, and an electrode. OPV cells rely on organic small molecules or polymers for light absorption and charge transport. Different from the traditional inorganic semiconductors where free electrons and holes are easily generated under solar illumination, in OPV device, neither bilayer and planar heterojunction structure or an intermixed bulk heterojunction (BHJ) structure, a strongly

the process of long-range resonance energy transfer.[92]

er extent through the emission of radiation.

102 Graphene - New Trends and Developments

organic synthesis reactions.[93, 94]

**4.1. Organic Photovoltaic (OPV)**

**4. Applications of photoactive graphene**

Graphene-involved semiconductor photocatalysts have attracted extensive attention because of their usefulness in environmental and green chemical catalyst applications.[99] Recently, photoactive-graphene-based photocatalysis has been widely used to catalyze various organic

**Figure 8.** GO/P3HT composite as a synergistic photocatalyst (Loh *et al*., *J. Phys. Chem. Lett.* 2012, *3*, 2332-2336).

reactions. For example, in Figure 8, photoactive graphene of noncovalently bonded graphene– polymer (P3HT) composite shows significant advancement of photocatalystic performance in Mannich reaction over commercial photocatalyst P25 (Loh *et al*., 2012).[100] Transient optical absorption studies have inferred that the tertiary amine is oxidized by the positive hole on the highest occupied molecular orbital (HOMO) of P3HT *via* single electron transfer to form the radical cation. At the same time, the excited electron is injected from the lowest unoccupied molecular orbital (LUMO) of P3HT into GO, which is then used to activate molecular oxygen to form the dioxygen radical anion; the latter can be stabilized by the aromatic scaffold in GO. [93] Pan *et al.* found that incorporation of Rose Bengal (RB) with GO sheet can provide higher catalyst actively of the visible light induced oxidative C-H functionalization of tertiary amines, even there was no direct physical interactions between RB and GO.[101]
