Novel Hyperbranched Molecules Containing Pyrrole Units from Diacetylene Compounds and their Electronic Properties
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Novel Hyperbranched Molecules Containing Pyrrole Units from Diacetylene Compounds and their Electronic Properties
Lioudmila Fomina1, Jorge Godínez Sánchez1, José A. Olivares2, Fabio L. CuppoSant´Anna2, Luis E. Sansores1 and Roberto Salcedo1 1
Instituto de Investigaciones en Materiales, Universidad Nacional Autónoma de México, Circuito Exterior s/n. C.U. A. Postal 70-360. Delegación Coyoacán. C.P. 04510. México D.F. México
2 Centro de Investigación en Polímeros, COMEX, Marcos Achar Lobaton No 2 Tepexpan, México, 55885
ABSTRACT Novel hyperbranched molecules containing pyrrole units were obtained from ortho-, metaand para-diaminodiphenyldiacetylenes, as AB2 type monomers by one-step polymerization. Diacetylenic fragments reacted with terminal amino groups in the presence of copper chloride to give pyrrole units. Diaminodiphenyldiacetylene monomers have been synthesized from ethynilanilines in three steps. The novel monomers and hyperbranched molecules were characterized by NMR, IR and thermal analysis. Some conductivity proofs were also carried out and this behavior was assessed. The electronic behavior of some of these molecules was studied by means of theoretical methods. DFT optimization processes were carried out for three structures derived from the generation growing. There are at least two conformational isomers of the structure (meta- and para-) which show conductivity properties, the meta-isomer shows semiconductor nature but this species is hard to modeling because the steric hindrances cause optimization problems and indeed the third generation species was not achieved. In other context, the para-isomer allows the calculation of three generations and shows clearly a tendency to narrow the energy gap between the frontier orbitals but besides the behavior of the HOMO-1 seems reinforce the conductivity phenomenon. INTRODUCTION In the last decades have been made several researches about the synthesis and characterization of many organic materials bearing highly conjugated structures. These materials exhibit semiconduction and non-linear optics properties, so that these compounds are used to elaborate electrochemical devices, organic light emitting diodes (OLEDs), rechargeable batteries, smart windows, among others. The dendrimeric polymers can be classified into three large groups [1]: a). The first one refers specifically to the basic dendrimers i.e. molecules which grow in branches [2] and they are prepared by in steps; b). The second group is formed by the so called dendro-injerted polymers [3] which have been described as the intermediated species between the dendrimers and the hyperbranched polymers; c). And the third group is constituted by the hyperbranched polymers [4, 5].There are several species which belong to the third group [6]. They are very interesting substances with highly branched structures, third dimensional
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architecture, globular shape, terminal functional groups and particular electronic behavior [5]; they can be prepared by polymeric one or several steps synthesis [6]. The diacet
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