Structural characterization of some Schiff base compounds: Investigation of their electrochemical, photoluminescence, thermal and anticancer activity properties Gökhan Ceyhan a , Muhammet Köse a , Mehmet Tümer a,n , İbrahim Demirtaş b , Ayse Şahin Yağlioğlu b , Vickie McKee c a Chemistry Department, Kahramanmaraş Sütcü Imam University, 46100 Kahramanmaraş, Turkey b Chemistry Department, Çankırı Karatekin University, 18100 Çankırı, Turkey c Chemistry Department, Loughborough University, LE11 3TU Leics, UK article info Article history: Received 11 January 2013 Received in revised form 27 March 2013 Accepted 5 June 2013 Available online 14 June 2013 Keywords: Schiff base Electrochemical X-ray Luminescence Anticancer abstract Three Schiff base compounds, N,N′-bis(2,4-dimethoxy benzaldiimine)-1,4-diamino cyclohexane (IGA 1 ), N,N′-bis(2,3,4-trimethoxy benzaldiimine)-1,4-diamino cyclohexane (IGA 2 ) and N,N′-bis(3,4,5-trimethoxy benzaldiimine)-1,4-diamino cyclohexane (IGA 3 ) were synthesized and characterized by the spectroscopic and analytical methods. The electrochemical and photoluminescence properties of the compounds IGA 1 – IGA 3 have been investigated in the different conditions. All the synthesized Schiff base compounds IGA 1 , IGA 2 and IGA 3 were screened for their cytotoxicity (HeLa and Vera cells). The structural characterization of the Schiff base compounds was determined by single crystal X-ray diffraction studies. The molecules IGA 1 and IGA 3 both lie on centers of symmetry but in IGA 2 the molecule has no crystallographically imposed symmetry. In the compound IGA 1 , Schiff base molecules are linked by π stacking interactions. There is no evidence of π stacking in both IGA 2 and IGA 3 , however there are some C–H⋯π and C–H…O interactions in these compounds. The thermal stabilities of the compounds were investigated in the nitrogen atmosphere. & 2013 Elsevier B.V. All rights reserved. 1. Introduction Schiff base condensation reactions of primary amines with aldehydes and ketones result in the formation of imines which contain a characteristic C¼ N double bond. Hugo Schiff described the condensation between an aldehyde and an amine leading to a Schiff base in 1864 [1]. Schiff bases decompose or polymerize rapidly unless there is at least one aryl group bonded to the nitrogen or the carbon atom of the C ¼ N double bond [2]. Schiff bases have played an important role in the development of coordination chemistry, as they readily form stable complexes with most of the transition metals exhibiting different coordination modes and functionalities [3,4]. Schiff bases, and nowadays active and well-designed Schiff base ligands are considered “privileged ligands” [5], because they are easily prepared by a simple one-pot condensation of aldehydes and primary amines in an alcohol solvent. Schiff bases have a wide variety of applications in many fields, e.g., biological, inorganic and analytical chemistry [6,7]. Application of many new analytical devices requires the presence of organic reagents as essential compounds of the measuring system. They are used in optical and electrochemical sensors, as well as in various chromatographic methods, to enable detection of enhance selectivity and sensitivity [8]. In addition, Schiff bases are able to stabilize many different metals in various oxidation states, controlling the performance of metals in a large variety of useful catalytic transformations. Metal complexes of these bases have numerous applications including antibacterial, antifungal [9,10] and antiviral activities [11] as well as other biological applications [12]. Several applications have been related for these complexes in chemical analysis [13], absorption and transport of oxygen [14], in pesticides [15] and heterogeneous and homogeneous catalysis for oxidation and polymerization of organic compounds [16,17]. Recently, we have synthesized and characterized a series of Schiff base ligands and their early and transition metal complexes [18–25]. They show excellent luminescence and electrochemical properties by providing proper conjugate absorption groups sui- table for energy transfer, which that could be used as a lumines- cent device. They also exhibit high antimicrobial and catalytic activity [23–25]. In the present work, three Schiff base compounds N,N′-bis (2,4-dimethoxy benzaldiimine)-1,4-diamino cyclohexane (IGA 1 ), N,N′-bis(2,3,4-trimethoxy benzaldiimine)-1,4-diamino cyclohexane (IGA 2 ) and N,N′-bis(3,4,5-trimethoxy benzaldiimine)-1,4-diamino Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/jlumin Journal of Luminescence 0022-2313/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jlumin.2013.06.002 n Corresponding author.: Tel.: +90 344 280 1444; fax: +90 344 280 1352. E-mail addresses: mtumer@ksu.edu.tr, gceyhan@ksu.edu.tr (M. Tümer). Journal of Luminescence 143 (2013) 623–634