ConspectusA major challenge in materials science is the ongoing search for coupling agents that are readily synthesized, capable of versatile chemistry, able to easily functionalize materials and surfaces, and efficient in covalently linking organic and inorganic entities. A decade ago, we began a research program investigating perfluorophenylazides (PFPAs) as the coupling agents in surface functionalization and nanomaterial synthesis. The p-substituted PFPAs are attractive heterobifunctional coupling agents because of their two distinct and synthetically distinguishable reactive centers: (i) the fluorinated phenylazide, which is capable of forming stable covalent adducts, and (ii) the functional group R, which can be tailored through synthesis.Two approaches have been undertaken for material synthesis and surface functionalization. The first method involves synthesizing PFPA bearing the first molecule or material with a functional linker R, and then attaching the resulting PFPA to the second material by activating the azido group. In the second approach, the material surface is first functionalized with PFPA via functional center R, and coupling of the second molecule or material is achieved with the surface azido groups. In this Account, we review the design and protocols of the two approaches, providing examples in which PFPA derivatives were successfully used in material surface functionalization, ligand conjugation, and the synthesis of hybrid nanomaterials.The methods developed have proved to be general and versatile, and they are applicable to a wide range of materials (especially those that lack reactive functional groups or are difficult to derivatize) and to various substrates of polymers, oxides, carbon materials, and metal films. The coupling chemistry can be initiated by light, heat, and electrons. Patterned structures can be generated by selectively activating the areas of interest. Furthermore, the process is easy to perform, and light activation occurs in minutes, greatly facilitating the efficiency of the reaction. PFPAs indeed demonstrate many benefits as versatile surface coupling agents and offer opportunities for further exploration.

Covalent functionalization of pristine graphene poses considerable challenges due to the lack of reactive functional groups. Herein, we report a simple and general method to covalently functionalize pristine graphene with well-defined chemical functionalities. It is a solution-based process where solvent-exfoliated graphene was treated with perfluorophenylazide (PFPA) by photochemical or thermal activation. Graphene with well-defined chemical functionalities was synthesized and the resulting materials were soluble in organic solvents or water depending on the nature of the functional group on PFPA. KeywordsGraphene; Azides; Covalent functionalization; Photochemistry Graphene, a material having a two-dimensional atomic layer of sp 2 carbon, has emerged as a nanoscale material with a wide range of unique properties. [1][2][3] In order to realize the many potential applications that graphene can offer, the availability of graphene with well-defined and controllable surface and interface properties is of critical importance. Despite the numerous studies on the properties and potentials of graphene, robust methods for producing chemically functionalized graphene are still lacking. 4,5 The most common method for the covalent functionalization of graphene employs graphene oxide (GO), 6 which is prepared by treating graphite particles with strong acids. 7 The oxidation process produces various oxygen-containing species, the nature and density of which are difficult to control.Covalent functionalization of pristine graphene poses considerable challenges due to its lack of reactive functional groups. Herein, we report a simple and general method for the covalent functionalization of pristine graphene. The approach is based on perfluorophenylazide (PFPA), 8,9 which upon photochemical or thermal activation, is converted to the highly reactive singlet perfluorophenylnitrene that can subsequently undergo C=C addition reactions with the sp 2 C network in graphene to form the aziridine adduct. We have confirmed the covalent bond formation between PFPA and graphene using X-ray photoelectron spectroscopy. 10,11 By controlling the functional group on the PFPA (Scheme 1), graphene with well-defined chemical functionalities can be prepared in a single step using a simple solution-based process.* To whom correspondence should be addressed. yanm@pdx.edu. PFPAs bearing alkyl (1), ethylene oxide (2), and perfluoroalkyl groups (3) (Scheme 1) were synthesized and used in this study (see Supporting Information for detailed synthesis and characterization of the compounds). These functional groups were chosen to impact the solubility and surface energy of the resulting graphene. Pristine graphene was prepared by exfoliating graphite in o-dichlorobenzene (DCB), a procedure that has been shown to produce graphene flakes in high yield. 12 Sonication of graphite in DCB followed by centrifugation gave a well-dispersed graphene solution, which was collected and used in the subsequent reactions. These graphene flakes consisted primarily of ...

We present a simple and efficient method to covalently immobilize graphene on silicon wafers using perfluorophenylazide (PFPA) as the coupling agent. Graphene sheets were covalently attached to PFPA-functionalized wafer surface by a simple heat treatment under ambient conditions. The formation of single and multiple layers of graphene were confirmed by Raman spectroscopy, and optical and atomic force microscopy. Evidence of covalent bond formation between graphene and PFPA decorated silicon wafer was given by X-ray photoelectron spectroscopy and sonication treatment.Graphene, a two-dimensional atomic thin layer of carbon nanostructure, has emerged as a unique nanoscale material with promising applications in electronics due to its stable crystal structure, optical transparency, and its exceptional electronic properties of high electron mobility and high saturation velocity for both electrons and holes [1][2][3][4][5][6][7] . However, realization of these potentials has been severely hampered by the availability of large-scale and stable graphene structures that are needed for electronic device fabrication. Furthermore, graphene films with well-defined and controllable surface and interface properties are important for both fundamental studies and practical applications of the material. 8,9 Among various reported preparation methods, 10-17 mechanical cleavage of highly oriented pyrolytic graphite (HOPG) remains to be the most popular and successful in producing single or few layers of graphene sheets. 18 The earliest approach involves the use of a Scotch tape to peel multiple layers of graphene from HOPG, and transfer the sheets to a substrate by pressing followed by releasing. The films obtained in this manner contain different numbers of graphene layers, and the percentage of single graphene sheets varies from sample to sample. An improved version of the mechanical cleavage technique involves applying external pressure to press HOPG on the substrate and thus physically transferring the material from HOPG to the substrate. 19,20 Chou and coworkers used the pillars on a stamp fabricated by nanoimprinting to cut and exfoliate graphene islands from HOPG, and then transferred the films from the stamp to the device active areas on a substrate. 19 Padture et al. fabricated a graphite stamp by etching into HOPG using the technique of photolithography. The HOPG stamp was then pressed onto a silicon wafer creating arrays of multi-layered graphene sheets on the substrate surface. 20 The graphene sheets deposited by these transferring methods are physisorbed on the substrate and can be easily removed by solvent wash (with isopropanol or acetone) or sonication. 21 Here, we report a method to covalently attach graphene to silicon wafers using perfluorophenylazides (PFPA) as the coupling agent. Upon photochemical or thermal activation, the azido group gives the highly reactive singlet perfluorophenylnitrene that can subsequently undergo C-H insertion and/or C=C addition reactions with the neighboring molecules (Scheme...

Producing large-scale graphene films with controllable patterns is an essential component of graphene-based nanodevice fabrication. Current methods of graphene pattern preparation involve either high cost, low throughput patterning processes or sophisticated instruments, hindering their large-scale fabrication and practical applications. We report a simple, effective, and reproducible approach for patterning graphene films with controllable feature sizes and shapes. The patterns were generated using a versatile photocoupling chemistry. Features from micrometres to centimetres were fabricated using a conventional photolithography process. This method is simple, general, and applicable to a wide range of substrates including silicon wafers, glass slides, and metal films.

Nanomaterials, possessing unique physical and chemical properties, have attracted much interest and generated wide varieties of applications. Recent investigations of functionalized nanomaterials have expanded into the biological area, providing a versatile platform in biomedical applications such as biomolecular sensing, biological imaging, drug delivery and disease therapy. Bio-functions and bio-compatibility of nanomaterials are realized by introducing synthetic ligands or natural biomolecules onto nanomaterials, and combining ligand-receptor biological interactions with intrinsic nanomaterial properties. Common strategies of engineering nanomaterial surfaces involve physisorption or chemisorption of desired ligands. We developed a photochemically initiated surface coupling chemistry, bringing versatility and simplicity to nanomaterial functionalization. The method was applied to attach underivatized carbohydrates efficiently on gold and iron oxide nanoparticles, and the resulting glyconanoparticles were successfully used as a sensitive biosensing system probing specific interactions between carbohydrates and proteins as well as bacteria.