Synthesis, structure, and complexation properties with transition metal cations of a novel methine-bridged bisquarylium dye

A new class of squarylium homologue, namely, an electronically neutral methine-bridged bisquarylium dye, was synthesized by a reaction of 4-(4-N,N-dialkylaminophenyl)-3-hydroxy-3-cyclobutene-1,2-dione with an excess amount of triethyl orthoformate. The X-ray crystallographic analysis revealed that the bisquarylium dye consists of two anilino-substituted cyclobutene components which are bridged with each other by a methine carbon. It was also confirmed that it possesses a highly delocalized pi-conjugation structure over the whole molecule. Its unique electronic structure yielded an intense light absorption in the near-infrared region. The complexation properties of the dye with various metal cations were investigated, and the complexation with transition metal cations such as Cr3+, Mn2+, Fe2+, Co2+ and Cu2+ exclusively induced drastic absorption spectral changes with hypsochromic shifts (Deltalambda; 59-197 nm). (C) 2002 Elsevier Science Ltd. All rights reserved.