Quantum Chemical Calculations of Reorganization Energy for Self-Exchange Electron and Hole Transfers of Aromatic Diamine
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Quantum Chemical Calculations of Reorganization Energy for Self-Exchange Electron and Hole Transfers of Aromatic Diamines as Electron-donor Molecules Qi Wei, Khishigjargal Tegshjargal, Davaasambuu Sarangerel, and Chimed Ganzorig Center for Nanoscience and Nanotechnology and Department of Chemical Technology, School of Chemistry and Chemical Engineering, National University of Mongolia, Ulaanbaatar, Mongolia ABSTRACT Reorganization energy is one of the important factors to decide the rate of electron transfer according to the Marcus theory. Small reorganization energy is highly desirable in design of optoelectronic and electronic devices like as organic light emitting diode. For this reason, reorganization energy of aromatic diamine derivatives, N,N′-diphenyl-N,N′-bis(3-methylphenyl)(1,1′-biphenyl)-4,4′-diamine (TPD) and 4,4′-diphenyl-N,N,N′,N′-tetraphenylbenzidine (DTPB) have been studied theoretically by self-exchange electron transfer theory. By executing the Gaussian 03 calculation we can easily figure out the optimization point which needed for calculation of the inner reorganization energy (λ) of self-exchange electron transfer reaction. Also ionization potential and electron affinities of these molecules can be calculated at the density functional theory level with basis set 6-31G** and 6-31G* using Gaussian 03 software on the basis of ab initio method. It gives possibility to develop a semi-empirical model for the observed absorption and photoluminescence spectrum. INTRODUCTION Electron transfer (ET) plays an important role in wide aspects of chemical, physical, and biological processes, and great progress has been made in theoretical perspective due to its fundamental nature [1]. Reorganization energy is the energy associated with relaxing geometry of the system after ET. For the convenience, the reorganization energy is usually divided into two parts: inner and outer reorganization energy, depending on which atoms are relaxed [2]. Inner reorganization energy relates to the change in equilibrium geometry of donor or accepter site due to gain or loss of electronic charge upon ET. Outer reorganization energy is due to electronic and nuclear polarization or relaxation of surrounding medium [3]. According to the Marcus theory, reorganization energy is the key factor to decide the rate of electron transfer and hole transfer devices such as organic field-effect transistor and organic light-emitting diodes. Small reorganization energy is highly desirable in the molecular design of optoelectronic and electronic materials. Extending the π-conjugation and employing a rigid molecular framework are effective factors for reducing the reorganization energy of organic molecules. Despite the importance of reorganization energy, precise measurements of this quantity are rather rare as it is difficult to measure the reorganization energy directly. Since theoretical calculation of reorganization energy is necessary and beneficial for prediction a novel design of optoelectronic and electronic materials. Various organic molecule
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