Thermal and Electron Impact Decomposition of 4-hydroxy-4'-cyano-azobenzene

* email: moantaanca@yahoo.com; Tel.: +40251-597048 4-Hydroxy-4'-cyano-azobenzene (HCA) is an azoic dye with various applications in organic synthesis. Thus, its derivatives attracted great attention in the last two decades due to their employment in the synthesis of photoresponsive azobenzene polymers. They have possible applications in non linear optics and optoelectronics and for optical information storage, thanks to laser-induced trans-cis-trans photoisomerization cycles of azobenzene cromophores [1]. Thus, certain teams used the HCA synthon in the synthesis of azobenzene side-chain-type copolymers with improved photoinduced anisotropy and long-term stability [2-4]. The photoinduced anisotropy in polythiophenes containing HCA derivatives was studied [5]. Recently, it was synthesised a photoresponsive polymer gel employing the coupling of HCA derivatives to αcyclodextrin ring by esterification [6]. Azocellulose polymers [7] have also been synthesized by coupling 4cyanophenylazophenol to the primary hydroxyl group of Dglucopyranose units of natural cellulose of ultrahigh molecular weight by the Mitsunobu reaction. Another class of polymers with application in holographic information storage was reported in [8] where a family of azobenzene peptides containing HCA was synthesized . HCA has also been integrated in photoresponsive trisurea compounds [9]. They act as self-assembled materials with light-induced photoswitchable properties due to the azo linkages. An interesting application of HCA was reported by [10] using this compound in the preparation of a new liquid crystal that can be used as stationary phase in gaschromatography. The structural formula of this azo dye was thoroughly investigated by several authors using different techniques (NMR, IR, UV-VIS) [1, 8, 9,11]. The mass spectrometry is important because it provides a lot of structural information with little expenditure of the sample. In electron impact (EI) mass spectra, the fragmentation consists of competitive and consecutive unimolecular fragmentation pathways [12,13]. The TG/DTA provides quantitative information on weight losses due to decomposition and/or evaporation of low molecular materials as a function of time and temperature. Due to the usage of azo dyes in special domains that require high temperatures, the investigation of their thermal stability is very important. Given this reason, the azo dyes were studied using thermogravimetric analysis [14-17]. The interpretation of thermal degradation processes can be supported by mass spectrometric analysis because the nature of the released volatiles may be thus deduced. The structure of 4-hydroxy-4'-cyanoazobenzene (HCA) is given in figure 1.