The synthesis, spectroscopic properties and crystal structures of some rhodanine merocyanine dyes for optical recording with a blue diode laser

Six rhodanine merocyanine dyes were synthesized via both a conventional solvent method and a microwave method using rhodanine, 2-methylthio quaternary salts and 1H-indole-3-carbaldehyde as starting materials. The products were identified using UV–Vis, IR, MS, 1H NMR and elemental analysis. The UV–Vis absorption spectra of the dyes in chloroform, DMSO, water, acetone, ethanol and methanol were investigated. The structures of two dyes (5a and 5b) were characterized and analyzed by X-ray diffraction as well. Crystallographic data revealed that dye 5a belonged to tetragonal, I4 (1)/a space group, while dye 5b belonged to monoclinic, P-1 space group. In the case of both dyes, intermolecular associations occurred by π–π stacking and intermolecular hydrogen bonds, which contributed to stabilize the crystal structure.

► Merocyanine dyes were synthesized by conventional method and microwave method.
► The synthesized dyes exhibited intensive absorption in blue light region.
► Two X-ray crystal structures were investigated in this work.
► The dyes have potential for optical recording with blue diode laser.