Self Organization in Thin Films of a Substituted Perylene Imide with a Twisted Aromatic Core
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0965-S09-05
Self Organization in Thin Films of a Substituted Perylene Imide with a Twisted Aromatic Core Harald Graaf1, Christine C Mattheus2,3, and Derck Schlettwein2 1 Institut für Physik, Technische Universität Chemnitz, Chemnitz, D-09107, Germany 2 Institute of Applied Physics, Justus-Liebig-Universität Giessen, Heinrich-Buff-Ring 16, Giessen, D- 35392, Germany 3 now at ASML, DR Veldhoven, NL-5504, Netherlands ABSTRACT The aromatic core of perylene bisimides can be twisted by chemical substitution with chlorine in the bay-position. An example for this strategy is 1,6,7,10-tetra-chloro-N,N’dimethyl-perylene-tetracarboxylic-bisimide, Cl4MePTCDI. This twisting leads to a decrease in directed intermolecular interactions, which causes a decrease in the electronic coupling of the molecules, interesting to be investigated in thin films of this molecular semiconductor. An amorphous solid phase was formed by physical vapor deposition. This amorphous phase showed the tendency to crystallize under ambient conditions as apparent von optical microscopy at the films. The crystallized phase was investigated by atomic force microscopy AFM and optical methods, where a formation of weak excimers was found.
INTRODUCTION Aside from the electronic properties of individual molecules, the intermolecular coupling of the electronic systems is of uttermost importance for the observed optical and electrical properties of organic semiconductor thin films [1,2]. Since the intermolecular coupling is greatly influenced by the relative intermolecular orientation, a high level of control over the intermolecular interaction is needed to achieve the desired optical and electrical characteristics for a given application [3-6]. Chemical substitution has a strong influence on the molecular energy levels [1,2] and on the geometrical arrangement of the molecules in solid particles and thin films [6-10] and can therefore determine greatly the intermolecular interactions, the electronic coupling and hence the electric and optic characteristics of the films. Perylene dyes are a good class of materials to probe this strategy and the transition from N,N’-dimethylperylene-3,4,9,10-bis(dicarboximide) (MePTCDI) to its chlorinated derivative 1,6,7,12-Tetrachloro-N,N’-dimethylperylene-3,4,9,10-bis(dicarboximide) (Cl4MePTCDI) is a good example [11,12]. Crystallized thin films are often characterized by a desired increased mobility of charge carriers,[12] but showed an increased tendency of excimer formation leading to quenching of the luminescence [11]. Besides this the ordered packing in a crystal hinders also a diffusion of larger gas molecules into the bulk, while in unstructured materials such a diffusion takes place more easily [13]. In this paper vapor-deposited films of the twisted 1,6,7,12-tetrachloro-N,N´dimethylperylene-3,4,9,10-bis(dicarboximide) (Cl4MePTCDI) [14] will be investigated. The structure of Cl4MePTCDI is shown in Figure 1.
Figure 1: Structure of Cl4MePTCDI
The four chlorine atoms at the bay-position lead to an twisting of the aromatic
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