Purification of PTCDA by Vacuum Sublimation and Spectral Test and Analysis

The organic semiconductor 3, 4, 9, 10 perylenetetracarboxylic dianhydride (PTCDA) with the purity of 97.5% was purified by sublimation to 99.9%. The high-purity PTCDA material was measured by mass spectra, infrared spectrum and X-ray photoelectron spectroscopy (XPS). Detailed analysis revealed its molecular structure, the forming of chemical bond, the vibration modes of atoms in equilibrium lattice position, electronic configuration and the shift of binding energy of atoms. Based on the infrared spectrum analysis, the molecular structure of PTCDA is consisting of perylene core group with five C rings and two anhydrides located at both ends of perylene core, which is mainly bonded with covalent bond. The stretching vibration of C atoms in the crystal lattice dominates in their equilibrium positions. The PTCDA molecules have a large number of π electrons which can move freely; the intermolecular delocalized π bond overlap determines the conductivity of PTCDA. Based on XPS analysis, it can be found that there exist two kinds of C atoms with different binding energy: 285.3 and 288.7 eV, respectively, corresponding to the C atoms in the perylene ring and anhydride. In addition, there are two kinds of O atoms, i. e. C==0 and C--O--C, whose bonding energy is 531.3 and 533.1 eV, respectively.