3972 DOI: 10.1021/la903335v Langmuir 2010, 26(6), 3972–3974 Published on Web 12/17/2009 pubs.acs.org/Langmuir © 2009 American Chemical Society Solubilized Derivatives of Perylenetetracarboxylic Dianhydride (PTCDA) Adsorbed on Highly Oriented Pyrolytic Graphite James C. Russell, † Matthew O. Blunt, † Gudrun Goretzki, ‡ Anna G. Phillips, ‡ Neil R. Champness, ‡ and Peter H. Beton* ,† † School of Physics and Astronomy, University of Nottingham, University Park, Nottingham, U.K., and ‡ School of Chemistry, University of Nottingham, University Park, Nottingham, U.K. Received September 4, 2009. Revised Manuscript Received November 20, 2009 The effect on 2D molecular crystallization caused by the addition of propylthioether side groups to the 3,4,9,10- perylenetetracarboxylic dianhydride (PTCDA) molecule is investigated using scanning tunneling microscopy (STM). The molecule was deposited from 1-phenyloctane onto highly oriented pyrolytic graphite (HOPG) and imaged at the liquid-solid interface. We observe a different structure to previously reported arrangements of PTCDA due to the presence of the propylthioether side groups which inhibits the formation of the herringbone phase. A model, supported by calculations based on density functional theory, is proposed in which molecules form rows stabilized by hydrogen bonding. Introduction The molecule perylenetetracarboxylic dianhydride, PTCDA, has been widely studied as a prototype active material for organic electronic devices. 1,2 PTCDA may be readily deposited by vac- uum deposition, and the properties of the resulting thin films have been investigated on a variety of different substrates including HOPG, 3,4 Ag(111), 5 Au(111), 6 Ag/Si(111)-( √ 3 Â √ 3), 7-9 Sn/Si(111)-(2 √ 3 Â √ 3), 10 and Cu(111). 11 In recent studies the interest in sublimed monolayers of PTCDA has been extended through the demonstration of the covalent coupling of adsorbed PTCDA to a variety of amine compounds, 12,13 leading to the identification of two-dimensional disordered polymers. This process is closely related to a reaction that occurs in solution phase where the substitution of the anhydride group with an alkane chain attached via an imide group leads to a family of compounds which have been widely investigated. 14-17 The addition of an imide-linked alkane chain promotes solu- bility of the resulting molecule, but the anhydride group of the PTCDA is eliminated through this coupling. In fact, and despite the extensive literature describing the adsorption of PTCDA under vacuum conditions, there have been very few studies of solution deposition of PTCDA due to its limited solubility. 18 Nevertheless, the controlled adsorption of arrays of molecules onto surfaces from a solution phase has become increasingly relevant to the fields of nanoscience and nanotechnology for the purposes of fabricating small electronic devices and sensors. 19,20 In this paper, we investigate a possible route to solubilizing PTCDA which leaves intact the anhydride functionality and show that such a modified derivative may be deposited on a substrate from a solution phase. The solubility is promoted by the intro- duction of a propyl chain attached to each side of the PTCDA molecule via a thioether link. The di(propylthio)perylenetetra- carboxylic dianhydride (DPT-PTCDA) molecule is shown in Figure 1. Experimental Section The DPT-PTCDA molecules were synthesized using the same procedure as summarized in previous work. 21 The molecules were dissolved in 1-phenyloctane (Sigma-Aldrich, 97% purity). A 10 μL droplet of solution was removed using a pipet and deposited onto a freshly cleaved HOPG surface. An Agilent 4500 series SPM was used to perform the imaging experiments in conjunction with the PicoScan control box and software. The STM was mounted in an isolation chamber with acoustic and vibrational damping to reduce environmental effects. Fresh STM tips were mechanically cut from 0.25 mm (80:20) PtIr wire before each experiment. The quality of the mechanically cut tips was *Corresponding author. E-mail: peter.beton@nottingham.ac.uk. (1) Forrest, S. R. Chem. Rev. 1997, 97, 1793–1896. (2) Schreiber, F. Phys. Status Solidi A 2004, 201, 1037–1054. (3) Hoshino, A.; Isoda, S.; Kurata, H.; Kobayashi, T. J. Appl. Phys. 1994, 76, 4113–4120. (4) Kendrick, C.; Kahn, A.; Forrest, S. R. Appl. 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