Design, synthesis and characterization of new trimethine oxonol dyes from 1,3-indandione and 2-substituted vinamidinium salts

Abstract

A series of novel cationic trimethine oxonol dyes with pyridinium substituents in the β-position of polymethine chain have been synthesized via an easy and efficient methodology by the condensation of 1,3-indandione with various substituted vinamidinium salts in ethanol as a green solvent without formation of any byproducts. The chemical structure of the synthesized dyes was investigated by FTIR, 1H NMR, 13C NMR, and HRMS techniques. The solutions of the new dyes in DMF absorbed visible light wavelengths at about 524–530 nm with narrow band widths and high molar absorption coefficients (around 1–2 × 105 dm3 mol−1 cm−1). They also exhibited fluorescence with a maximum emission intensity at about 700 nm and a relatively large (about 171–176 nm) Stokes shift. An optimized geometrical configuration of the dyes has been determined by using the density functional theory (DFT) at B3LYP/6-311G(d,p) theoretical level.