Crystal structures of a benzoselenazole-derived squarylium cyanine dye and three derivatives substituted at the central squaric ring

Abstract

The crystal structures of 4-[(3-hexylbenzoselenazol-3-ium-2-yl)methylidene]-2-[(3-hexyl-3H-benzoselenazol-2-ylidene)methyl]-3-oxocyclobut-1-en-1-olate and its analogues substituted at the squaric ring with O-methyl, NH-methyl and N,N-diethylamino groups have been determined using single crystal X-ray crystallography techniques. The unsubstituted squaraine dye is symmetrical and packs as a stepped ribbon array (via a C–H⋯O close interaction), which is in contrast to the slip-stacked arrangements observed in similar squaraine analogues. Each of the substituted analogues is asymmetric and pack in slightly differing slip-stacked charge-transfer columns. The NH-methyl analogue packs with a single water molecule per squaraine unit.