Synthesis and sensing behavior of cyanoanthracene modified 1,3-alternate calix[4]benzocrown-6:: a new class of Cs+ selective optical sensors

1,3-Calix[4]bis (10-cyano-9-anthrylmethyl-o-benzocrown-6) AnCN2, and 1,3-calix[4]-25,27-bis(allyloxy)-26,28-(10-cyano-9-anthrylmethyl-o-benzocrown-6), AnCN1, were synthesized as the first generation of Cs+ selective optical sensors based on calixarenes. The maximum enhancement in the emission of AnCN2 and AnCN1 upon Cs' complexation was 11.7 and 8.2 in a 1 : 1 CH2Cl2-MeOH mixture. Their response to Various alkali metal ions follows the order Cs+ > Rb+ >> K+ >> Na+ > Li+ indicating good selectivity towards caesium. The fluorescence and absorption profile for CS' complexation suggest a 1 : 1 stoichiometry for the host AnCN1-Cs complex and a stability constant of 10(7) M-1. AnCN2, on the other hand, shows two plateau regions corresponding to a 1 : 2 stoichiometry for complexation of Cs'. The first complexation constant is much higher (10(7) M-1) than the second one (10(4) M-1). The NMR studies further substantiate the complexation of two metal ions by AnCN2. This is the first report of stepwise complexation of metal ions to a 1,3-alternate calix[4]bis(crown-6) derivative.