Photolytic discoloration of azo dye incorporated organoiron polymer A.S. Abd-El-Aziz * , B. Elmayergi, B. Asher, T.H. Afifi, K.J. Friesen Department of Chemistry, University of Winnipeg, 515 Portage Avenue, Winnipeg, Man., Canada R3B 2E9 Received 27 November 2005; accepted 31 December 2005 Available online 21 February 2006 This paper is dedicated to Professor Brian James in celebration of his 70th birthday, as well as in recognition of his outstanding contribution to chemistry. Abstract Organoiron polymers with azo dyes pendant to the backbone incurred loss of color upon irradiation with UV light (k = 300 nm) in acetonitrile solution. The loss of color is attributed to the interaction of the cleaved iron moiety with the azo chromophore. Similarly, addition of small amounts (61 mM) of both Fe(II) and Fe(III) to the organic polymer analogue yielded comparable discoloration rates upon irradiation. The iron cation forms a complex with the azo chromophore group in the polymer, and subsequently leads to the pho- todegradation of the azo dye. At higher initial polymer concentrations, minimal discoloration was observed due to the light attenuation effect of the deeply colored solutions. In the presence of small amounts of water, the iron cation is inhibited from partaking in complex formation and no polymer discoloration was observed. For the organic polymer analogue, the presence of water did not show significant change over its absence upon irradiation. The discoloration of the polymer relies solely on its interaction with the iron cation present in solution, and does not require addition of any catalyst or reagent. This process might be developed into a pragmatic and viable method for the treatment of specifically designed colored materials using only UV light. Ó 2006 Elsevier B.V. All rights reserved. Keywords: Azo dye; UV-light; Organoiron complexes; Organoiron polymers, Discoloration; Photolysis; Iron cation; Synthesis 1. Introduction Organometallic polymers have been a topic of recent focus due to their interesting electrical, catalytic, physical, and chemical properties [1–3]. Transition metal coordi- nated complexes have received considerable interest, in particular Cr(CO) 3 , Mo(CO) 3 , Mn(CO) 3 , CpFe + and Cp * Ru + , for their design of novel molecules [4–8]. The elec- tron withdrawing ability of the transition metal moiety affords nucleophilic aromatic substitution and addition reactions, which were not allowed through traditional organic routes [9–12]. Our research group has utilized the reactions of cationic g 6 -chloroarene-g 5 -cyclopentadienyl- iron complexes with varying nucleophiles to produce novel organoiron complexes [13–19]. The incorporation of azo chromophores into these high molecular weight materials introduces unique nonlinear optical properties to the polymer, exhibiting functionality in optical storage devices, electrooptic modulators and sec- ond harmonic generators [20]. We have recently reported the synthesis of a number of neutral and cationic iron-con- taining polymers with azo dyes either directly in the back- bone or pendant to the polymer [21–23]. These polymerization reactions occurred under mild conditions due to the exceptional electron-withdrawing capability of the cyclopentadienyliron cations (CpFe + ). The resulting organoiron polymers exhibited good to excellent solubility in polar organic solvents [24,25]. Azo-incorporated synthe- sized polymers had wavelength maxima similar to the cor- responding monomers, and exhibited characteristic ammonium and azonium bands on acidification. Photolytic demetallation with exposure to 300 nm light cleaves the CpFe + moiety from the polymer backbone, allowing for the isolation of the organic analogue. The corresponding 0020-1693/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.ica.2005.12.061 * Corresponding author. Tel.: +1 204 786 9944; fax: +1 204 783 8910. E-mail address: a.abdelaziz@uwinnipeg.ca (A.S. Abd-El-Aziz). www.elsevier.com/locate/ica Inorganica Chimica Acta 359 (2006) 3007–3013