Fluoroponytailed Brooker's merocyanines

Abstract

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 specificwavelengths. 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.