Synthetic Metals 159 (2009) 659–665 Contents lists available at ScienceDirect Synthetic Metals journal homepage: www.elsevier.com/locate/synmet A comparative investigation between poly(1-ethynylpyrene) and poly(1,6-(3-ethynylpyrenylene)): Influence of the structure on the thermal, optical, electrochemical properties and conductivity Juan Manuel Reyna-González a , Martha Aguilar-Martínez b , Alberto García-Concha a , Celso Palomar, Ernesto Rivera a,∗ a Instituto de Investigaciones en Materiales, Universidad Nacional, Autónoma de México, Circuito Exterior Ciudad Universitaria, C.P. 04510, México D.F., Mexico b Facultad de Química, Universidad Nacional Autónoma de México, Ciudad Universitaria, C.P. 04510, México D.F., Mexico article info Article history: Received 13 February 2008 Received in revised form 1 December 2008 Accepted 17 December 2008 Available online 23 January 2009 Keywords: Pyrene Polymer Thermal and optical properties Electrochemistry abstract A comparative investigation between trans-poly(1-ethynylpyrene) (trans-PEP) obtained chemically and poly(1,6-(3-ethynylpyrenylene) (E-PEP) prepared electrochemically was carried out. Thermal and opti- cal properties of the polymers were studied by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and absorption spectroscopy. Electrochemical properties were evaluated by cyclic voltamperometry, in a 0.1M Et 4 NClO 4 /THF solution at 10mV/s, using a Pt disc as working electrode and Ag/AgCl as reference electrode. On the other hand, the conductivity of both polymers was measured in pressed pellet. Trans-PEP (T 10 = 369 ◦ C) showed a higher thermal stability than its homologue E-PEP (T 10 = 256 ◦ C). DSC of the polymers showed that trans-PEP exhibits a softening point at 330 ◦ C, whereas E- PEP does it at 117 ◦ C. Absorption spectra of the polymers revealed that trans-PEP exhibits two absorption bands at  = 336 nm and  = 580 nm due to the pyrene moieties and the highly conjugated polyacetylene main chain, respectively. By contrast, E-PEP showed only an absorption band at  = 358 nm followed by a tail, which reveals that this polymer possesses a lower degree of conjugation. Molecular modelling per- formed in short segments of these polymers confirmed this hypothesis. Regarding the electrochemical properties, trans-PEP showed an anodic peak at 1500mV and a conductivity value  = 2.7 × 10 -2 S/cm, whereas E-PEP exhibited an anodic oxidation peak at 1670mV and  = 8.4 × 10 -2 S/cm. © 2008 Elsevier B.V. All rights reserved. 1. Introduction In the last 30 years, -conjugated polymers have been con- sidered as promising materials for the development of various opto-electronic devices such as light emitting diodes, photo- voltaic cells and non-linear optical systems among others. The opto-electronic properties vary considerably depending on the extent of conjugation length between the consecutive repeat units [1–9]. Previously, we reported the chemical polymerization of 1- ethynylpyrene (EP) and other related monomers under different reaction conditions [10,11]. Catalytic polymerization of EP with WCl 6 resulted in the formation of trans-poly(1-ethynylpyrene) (trans-PEP) with molecular weights ranging from 24,000 to 470,000g/mol and polydispersities between 2.9 and 11 [10]. Poly- merization of EP was also carried out using the catalytic system (1-Me-Indenyl)(PPh 3 )Ni–C C–Ph and methylaluminoxane (MAO) ∗ Corresponding author. Tel.: +52 55 56 22 47 33; fax: +52 55 56 16 12 01. E-mail address: riverage@iim.unam.mx (E. Rivera). [11]. This method provided the formation of soluble cis-transoidal poly(1-ethynylpyrene) (cis-PEP) with weight-averaged molecular weights (M w ) ranging from 2200 to 24,000 g/mol and polydis- persities about 2. In both cases, the polymerization takes place exclusively through the triple bond present in the monomer. Fur- thermore, we reported a comparative investigation between the thermal, optical, electrochemical properties and conductivity of poly(1-ethynylpyrene) in function of the main configuration of the polymer backbone and the internal stacking of the pendant pyrenyl groups [12,13]. We selected pyrene containing monomers to carry out this study, because pyrene is an efficient fluorescent probe, which has been successfully used as molecular label in the study of a huge variety of polymers [14–24]. In this work, we report a compara- tive study between polypyrenylacetylenes obtained chemically and electrochemically. The chemical and electrochemical polymeriza- tion of 1-ethynylpyrene is illustrated in Fig. 1. Thermal, optical, electrochemical properties and conductivity of these polymers were studied in detail, and the results were analyzed, compared and correlated with the optimized geometries predicted by molecular modelling. 0379-6779/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.synthmet.2008.12.012