Fluoroponytailed Brooker's merocyanines: Studies on solution behavior, solvatochromism and supramolecular aggregation

• Published in: Dyes and pigments Vol. 184; p. 108798
• Main Authors: Fliri, Lukas, Partl, Gabriel, Winkler, Daniel, Laus, Gerhard, Müller, Thomas, Schottenberger, Herwig, Hummel, Michael
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01-01-2021
• Subjects: Brooker's merocyanine; Concentration dependent coloration; Dye-aggregation; Fluoroponytail; Micelle formation; Solvatochromism; Solvatochromism; Concentration dependent coloration; Micelle formation; Fluoroponytail; Dye-aggregation; Brooker's merocyanine
• ISSN: 0143-7208; 1873-3743
• DOI: 10.1016/j.dyepig.2020.108798

In this investigation, influences on solution behavior and solvatochromism caused by the attachment of a 1H,1H,2H,2H-perfluorooctyl side chain onto derivatives of the well-known Brooker's Merocyanine (BM) chromophore are explored. Starting from either 4-picoline or 2-picoline, the corresponding polyfluoroalkylated o- and p-BM have been synthesized in three steps. For all dyes, UV–Vis measurements were conducted in 21 different solvents. An attempted analysis of solvatochromic properties applying linear fits according to Kamlet-Taft parameters turned out to be partially inconclusive and was only feasible for five of the novel dyes after careful examination of their UV–Vis spectra. The observed changes of the spectral characteristics, in combination with the occurrence of either strong hypsochromic or bathochromic shifts, were too significant to be only ascribable to the influence of the solvating medium. Additionally, the maxima of different dyes in different solvents exposed tendencies to converge at specific wavelengths. Taking into account that both, merocyanines as well as fluorosurfactants are known for their formation of supramolecular assemblies, we suggest that aggregation is responsible for the observed phenomena, although controversially disputed in the preliminary literature concerning BM. To underline our proposal, concentration dependent UV–Vis measurements were supplemented.
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•Synthesis of ten fluoroponytailed Brooker’s Merocyanines containing different auxochromes for a systematic UV-Vis study.•Detection of striking aberrations of Lambert-Beer's law, strongly suggesting the formation of supramolecular aggregates.•Concentration dependent coloration of dilutions of 5c in EtOH, ranging from pale yellow to intensely blue.•Profound negative solvatochromic shifts (Δλ). For 5c a Δλ of 262 nm is observed between H2O (398 nm) and CHCl3 (660 nm).