Covalently Patterned Graphene Surfaces by a Force-Accelerated Diels-Alder Reaction Shudan Bian, † Amy M. Scott, † Yang Cao, ‡ Yong Liang, ‡ Sílvia Osuna, ‡ K. N. Houk,* ,‡ and Adam B. Braunschweig* ,† † Department of Chemistry, University of Miami, Coral Gables, Florida 33146, United States ‡ Department of Chemistry and Biochemistry, University of California, Los Angeles, Los Angeles, California 90095, United States * S Supporting Information ABSTRACT: Cyclopentadienes (CPs) with Raman and electrochemically active tags were patterned covalently onto graphene surfaces using force-accelerated Diels- Alder (DA) reactions that were induced by an array of elastomeric tips mounted onto the piezoelectric actuators of an atomic force microscope. These force-accelerated cycloadditions are a feasible route to locally alter the chemical composition of graphene defects and edge sites under ambient atmosphere and temperature over large areas (∼1 cm 2 ). G raphene has become the focus of much research attention because of its high conductivity, 2D structure, and superior mechanical properties. 1 Patterning onto the basal plane of graphene may increase the bandgap of graphene, a boon for integrated optics and electronics, or for the fabrication of graphene-based sensors. 2 However, a consequence of the stabilizing π-conjugation of graphene is that the basal plane is resistant toward chemical functionalization; thus, carrying out organic chemistry on graphene site-specifically is particularly challenging. Scalable methods to covalently pattern organic molecules onto graphene have not, to the best of our knowledge, been demonstrated. Functional molecules have been anchored to graphene using noncovalent interactions 3 or bonding to oxidized defect sites and edges. 2d,4 Alternatively, photochemical, 5 dipolar-cycloadditions, 6 and diazonium salt 2b,7 reactions couple organics directly with the basal plane of graphene, albeit not in patterns and with an input of energy that would denature or destroy soft matter. The recent report by Haddon et al. proposing that single layer graphene (SLG) participates in DA reactions as a dienophile at temperatures as low as 50 °C over 3 h 8 suggested to us conditions that could be used to scalably pattern graphene at ambient temperatures and atmosphere. Because of their negative activation volumes, 9 cycloaddition reactions are significantly accelerated in pressur- ized reaction vessels, and the Reinhoudt and Ravoo groups have covalently micropatterned various surfaces by inducing Cu I -free Huisgen and DA reactions through applied force between inked elastomeric stamps and surfaces. 10 Thus, we reasoned that a localized force exerted between SLG and a diene would accelerate the DA reactions and thereby immobilize molecules into patterns onto the basal plane of graphene through the formation of two new C-C bonds (Figure 1a). To demonstrate that force-accelerated cycloadditions could covalently pattern large areas (∼1 cm 2 ) of SLG sheets, we used an elastomeric tip array mounted onto the piezoelectric actuators of an atomic force microscope (AFM) to exert a localized force between functionalized CPs and SLG sheets. These tip arrays are commonly used for polymer pen lithography, 11 where patterns are formed by ink transfer from the tips to the surface through an aqueous meniscus. Moreover, their large areas (>1 cm 2 ) and the computer-controlled movement of the piezoactuators that hold the array provide high throughput and flexible pattern design. We have recently induced both the Cu I -catalyzed azide-alkyne click reaction 12 and the Staudinger ligation 13 on Au and SiO 2 surfaces with these tip arrays under ambient temperatures and pressures, confirming the suitability of these tip arrays for covalently immobilizing soft matter nondestructively through selective organic transformations. Because the elastomeric tips also Received: August 1, 2012 Published: June 11, 2013 Figure 1. (a) DA oligomerization reaction between functionalized CP and a SLG surface. (b) Cy3-containing Raman active 1 and ferrocene- containing electrochemically active 2 ink molecules used to confirm force-accelerated patterning. (c) An elastomeric tip-array. (d) The tip- array coated with an ink mixture (red) consisting of a CP and poly(ethylene glycol) (PEG). (e) The inked tip array is pushed into the SLG surface. (f) Following rinsing of the surface to remove the PEG and excess CP, only the covalently immobilized molecules remain on the surface. Communication pubs.acs.org/JACS © 2013 American Chemical Society 9240 dx.doi.org/10.1021/ja4042077 | J. Am. Chem. Soc. 2013, 135, 9240-9243