Synthesis and optical properties of novel thermally stable bis-merocyanine dyes

A new series of thermally stable linked bis-merocyanine dyes were synthesized from thiazolium salt derivatives and bis-rhodanines in good yields. The synthesized compounds were fully characterized by FT-IR, UV/Vis, NMR and mass spectrometry and their thermal properties were determined by TGA and DSC. The shape of the absorption spectra of bis-merocyanine dyes is affected both by the nature of the spacer and the polarity of the solvent. Absorption and fluorescence spectra of compound B1T6 were measured at room temperature (298 K), in various solvents to investigate their solvatochromic behaviour. The ground and excited state dipole moments of B1T6 compound were estimated experimentally by solvatochromic shift method using Bilot-Kawski, Lippert-Mataga, Bakhshiev, Kawski-Chamma-Viallet and Reidchardt's microscopic solvent polarity functions. It was observed that the excited-state dipole moment was found to be higher than the corresponding ground-state dipole moments, due to a substantial redistribution of electron densities and charges in a more polar excited-state. The geometry of this compound was optimized; HOMO-LUMO energy values and the ground state dipole moment mu g were also evaluated theoretically by quantum chemical calculations using the DFT method by adopting B3LYP/G-31 G (d, p) of theory (Gaussian 09). (C) 2019 Elsevier B.V. All rights reserved.