29582 | Phys. Chem. Chem. Phys., 2016, 18, 29582--29590 This journal is © the Owner Societies 2016 Cite this: Phys. Chem. Chem. Phys., 2016, 18, 29582 Modulation of the exfoliated graphene work function through cycloaddition of nitrile imines†‡ Myriam Barrejo ´ n, a Marı ´ a J. Go ´ mez-Escalonilla, a Jose ´ Luis G. Fierro, b Pilar Prieto, c Jose ´ R. Carrillo, c Antonio M. Rodrı ´ guez, cd Gonzalo Abella ´ n, e M a Cruz Lo ´ pez-Escalante, f Mercedes Gaba ´ s, g Juan T. Lo ´ pez-Navarrete h and Fernando Langa* a After the feasibility of the 1,3-dipolar cycloaddition reaction between nitrile imines and exfoliated graphene by density functional theory calculations was proved, very few-layer graphene was effectively functionalized using this procedure. Hydrazones with different electronic properties were used as precursors for the 1,3-dipoles, and microwave irradiation as an energy source enabled the reaction to be performed in a few minutes. The anchoring of organic addends on the graphene surface was confirmed by Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and thermogravimetric analysis. Ultraviolet photoelectron spectroscopy (UPS) was used to measure the work function and band gap of these new hybrids. Our results demonstrate that it is possible to modulate these important electronic valence band parameters by tailoring the electron richness of the organic addends and/or the degree of functionalization. 1. Introduction Graphene is a two-dimensional material that is composed of a single layer of carbon atoms and it has recently attracted considerable scientific interest due to its significant physical properties and a large number of potential technological applications. 1–3 Graphene is characterized as a zero band gap semimetal in which the conduction and the valence bands meet at the Dirac point. The zero bandgap nature of graphene results in a high current leakage, which limits its applications as a candidate in standard logic electronic circuits. In this regard, the intro- duction of a bandgap in graphene through band structure engineering 4–7 into a semiconductor by opening up the band gap, and thus enhancing its potential practical electronic applica- tions is highly desirable. 8,9 Covalent chemistry provides a powerful pathway to tailor the physical properties of pristine graphene to transform intrinsic zero band gap energy graphene. Based on the well-known covalent chemical reactivity of fullerenes and carbon nanotubes, chemists have already achieved good control of the elemental covalent chemistry of graphene and a broad arsenal of chemical reactions have already been carried out on this flat form of carbon, despite its low chemical reactivity when compared with curved carbon nanostructures such as fullerenes and carbon nanotubes. 10–13 Cycloaddition chemistry is clearly an important tool in the chemistry of carbon nanostructures. The application of this chemistry leads to higher solubility, better control over composition and the development of more complicated carbon nanostructure archi- tectures for novel properties and new applications. The most frequently employed type of cycloaddition in carbon nano- structure chemistry is arguably the 1,3-dipolar cycloaddition and, in particular, the cycloaddition of azomethine ylides. 14,15 Nevertheless, nitrile imines, formed in situ in a one-pot pro- cedure from hydrazones and N-bromosuccinimide (NBS) or a Universidad de Castilla-La Mancha, Instituto de Nanociencia, Nanotecnologı ´a y Materiales Moleculares (INAMOL), 45071, Toledo, Spain. E-mail: Fernando.Langa@uclm.es b Instituto de Cata ´lisis y Petroleoquı ´mica, CSIC, Cantoblanco, 28049, Madrid, Spain c Departamento de Quı ´mica Orga ´nica, Inorga ´nica y Bioquı ´mica, Facultad de Ciencias y Tecnologı ´as Quı ´micas, Universidad de Castilla-La Mancha, Campus Universitario, 13071 Ciudad Real, Spain d Dipartimento di Scienze Chimiche, Universita ` degli Studi di Napoli Federico II, Via Cintia, 80126, Naples, Italy e Department of Chemistry and Pharmacy and Institute of Advanced Materials and Processes (ZMP), Friedrich Alexander University Erlangen-Nu ¨rnberg, Henkestrasse, 42, 91054 Erlangen and Dr.-Mack Strasse 81, 90762 Fu ¨rth, Germany f Unidad de Nanotecnologı ´a - The Nanotech Unit Dpto. Ingenierı ´a Quı ´mica, Lab. Materiales & Superficies, Universidad de Ma ´laga, 29071 Ma ´laga, Spain g Unidad de Nanotecnologı ´a - The Nanotech Unit Dpto. Fı ´sica Aplicada I, Lab. Materiales & Superficies, Universidad de Ma´laga, 29071 Ma ´laga, Spain h Department of Physical Chemistry, University of Ma´laga, Campus de Teatinos s/n, 29071, Ma ´laga, Spain † Dedicated to Prof. Tomas Torres on the occasion of his 65th birthday. ‡ Electronic supplementary information (ESI) available: Additional data of TGA plots and Raman, XPS and FTIR data, AFM and HRTEM images, VBA spectra and also computational details. See DOI: 10.1039/c6cp05285a Received 29th July 2016, Accepted 27th September 2016 DOI: 10.1039/c6cp05285a www.rsc.org/pccp PCCP PAPER Published on 30 September 2016. Downloaded by Universitat Erlangen Nurnberg on 02/01/2018 13:32:10. View Article Online View Journal | View Issue