Near-IR region absorbing 1,4-diaminoanthracene-9,10-dione motif based ratiometric chemosensors for Cu 2þ Navneet Kaur, Subodh Kumar * Department of Chemistry, Guru Nanak Dev University, Amritsar 143005, India Received 18 August 2007; received in revised form 17 December 2007; accepted 25 January 2008 Available online 31 January 2008 Abstract 1,4-Bis[2-aminoethylamino]anthracene-9,10-diones selectively bind with Cu 2þ to form complexes with unusual selectivity under basic conditions. The deprotonation of the aryl amine NH in the case of these chemosensors causes a bathochromic shift in the absorption band from 585 nm and 635 nm to 725 nm and enables ratiometric estimation of Cu 2þ between pH 8 and 12. Ó 2008 Published by Elsevier Ltd. 1. Introduction The understanding of the molecular interactions between different chemical entities is the key to the development of chemical sciences and many interdisciplinary areas, which share boundaries with chemical sciences. The availability of tools to understand and evaluate such molecular interactions has resulted in enormous expansion of knowledge in the design of new drug entities (receptoreligand interactions) 1 and studies in new abiotic receptors (supramolecular science) 2 for the past half century. Anthracene-9,10-diones due to their diverse chemical features depending on the substitution pattern have shown widespread potential for the development of dye stuff materials, 3 DNA-inter- calating molecules, 4 redox active 5 and optical sensors. 6 Recently, we have reported that aminoethyl functional groups bearing anthracene-9,10-diones (Fig. 1) effectively bind Cu 2þ amongst various alkali, alkaline earth and transition metal ions. 7 The variation in substituent nature and their posi- tion on the anthracene-9,10-dione platform effectively controls the stability of their Cu 2þ complexes across various pH ranges. The presence of the aminoethylamino moiety at position 1 (1a and 1b) and positions 1,8 (2a and 2b) leads to most stable complexes with Cu 2þ between pH 6 and 8 while above pH 8, the increased concentration of hydroxyl anions, probably due to formation of Cu(OH) 2 , results in decomplexation of the complex, which could be controlled by increasing the hydrophobic environment around anthracene-9,10-dione in 1c. 1,4-Bis[2-aminoethylamino]anthracene-9,10-diones are one of the most effective DNA intercalators 4 and one such deriva- tive, mitoxantrone, has been in clinical use for more than three decades. More recently, their derived systems have found appli- cations as anion sensors. 6 In biochemical processes, due to the presence of a large number of components, the possibility of the interaction of the molecule under study with a species other than the target receptor can significantly affect the overall interaction with O O HN N R R O O HN NH N N R R R R 1a. R = H 1b. R = CH 3 1c. R = CH 2 CONHC 8 H 17 2a. R = H 2b. R = CH 3 Figure 1. Structures of sensors 1 and 2. * Corresponding author. Fax: þ91 183 2258820. E-mail address: subodh_gndu@yahoo.co.in (S. Kumar). 0040-4020/$ - see front matter Ó 2008 Published by Elsevier Ltd. doi:10.1016/j.tet.2008.01.095 Available online at www.sciencedirect.com Tetrahedron 64 (2008) 3168e3175 www.elsevier.com/locate/tet