The organic Light Emitting Diodes (OLEDs) have been attracting considerable interest due to low cost of production and their use in producing flexible electronic materials. Poly [2-methoxy-5-(20-ethylhexyloxy)-1,4-phenylene] vinylene (MEH-PPV) is one of the most interesting materials that can be applied as OELDs due to its electroluminescent characteristic in the visible region of the electromagnetic spectrum. Poly (3,4 ethylenedioxithiophene) (PEDOT) has been investigated for applications in flexible organic solar cells. Computational chemistry methods are good tools for molecular investigation of organic semiconductors because of the possibility to compare molecular geometries and electronic properties for better understanding of charge mobility as a function of geometrical parameters that can be modified. In this work, we present a semi-empirical study for MEH-PPV and PEDOT systems using three methodologies, PM6, PM7 and RM1 to study the stabilization energy and gap energy behavior with chain length. The results showed that PM6 methodology better describes the chain length for both systems, where heavy atom energy become stable from certain monomeric units for MEH-PPV and PEDOT chain length. Furthermore, by PM6 methodology, gap energy produces asymptotic behavior with chain length, with closer agreement with experimental results than other methodologies. In addition, PM6 methodology provides the best geometry for large oligomers, proving the ability of this methodology to produce good results for organic semiconductor systems.
Keywords: MEH-PPV, MOPAC, PEDOT, PM6, PM7, RM1, semi-empirical methods.
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