Styryl dyes, preparation

The heterocyclic quaternary salt l,3-diethyl-2-methyl-5-(iV-trifluoromethylsul-fonyl -trifluoromethylsulfoximido)-l -benzimidazolium tosylate, containing the superstrong electron acceptor (ap = 1.4) group CF3S(0)=NS0 2CF 3, was prepared and used as an intermediate for carbocyanine, merocyanine, and styryl dyes. The spectra of these dyes showed a large bathochromic shift compared with the... 

Trimethyloxindole is usually prepared by permanganate oxidation of Fischer s base.36 Cyanine, merocyanine (including spiropyran), and styryl dyes made from Fischer s base also give the oxindole upon thermal or photodegradation in air. The accumulated pot residues from the distillation of Fischer s base and the concentrates from dye preparations can be recycled by simply treating these chemical wastes with air (or better, hydrogen peroxide), preferably in the presence of visible light. The trimethyloxindole is recovered by a simple vacuum distillation in about 50% yield (from Fischer s base still residues).7... 

Sulfonation of Fischer s base in 30% oleum gives a 97% yield of the 5- and not the 6-substituted derivative, according to NMR spectral evidence. The compound was used to prepare cyanine and styryl dyes, but no spiropyrans were reported.44... 

The resolution of 3-phenylFischer s base itself would make available the chiral base for the preparation of not only indolinospiropyrans, but also for cyanine, merocyanine, and styryl dyes. Several attempts to effect this resolution using the camphorsulfonic, bromocamphorsulfonic, and dibenzoyltartaric acids in lower alcohols, 1,2,-dimethoxyethane and tetrahydrofuran, were unsuccessful in giving a clean resolution. Perseverance and luck are of prime importance. 

Fluorescent styryl dyes such as FMl-43 have been used to approximate neurotransmitter release by measuring rates of ex-ocytosis (16, 72, 73). These dyes reversibly label endosomal membranes and can be taken up into intracellular synaptic vesicles during endocytosis in systems in which vesicle recycling takes place. Typically, tissue is incubated in the fluorescent dye and then stimulated to promote vesicle cycling and therefore uptake of the dye. The preparation then is washed in fresh buffer to remove dye that remained extracellular. Using fluorescent microscopy, vesicle dynamics can be tracked. Neurotransmitter release is estimated from the rate of destaining (because of exocytosis) usually during stimulation. 

Aryl dyes may be prepared by forming a methine chain between a quaternary salt of a heterocyclic compound having a methyl group in the 2- or 4-position and an aryl compound, e.g. PAHs [6]. The best known compounds in this group are the styryl dyes. Following a synthetic route similar to that used in the preparation of styryl dyes, other dyes containing aryl groups may be prepared. For example, styryl dyes are prepared by the condensation of benzaldehydes with the quaternary salt of heterocyclic compounds [6]. 

Li et al. reported the first solid-phase synthesis of a DOFL based on the styryl structure." Styryl compoimds are simple fluorescent molecules that can be prepared by condensation of aldehydes and pyridinium salts. After testing a series of resins and reaction routes, the authors employed a 2-chlorotrityl polystyrene resin to load two amino alcohols with different length chains. The alcohol groups were then mesylated and subsequently treated with four picoline and three quinoline derivatives to render solid-supported pyridinium salts that were then condensed with 64 chemically diverse aldehydes under microwave irradiation (Figure 14.9a). Final cleavage with TFA-DCM (1 99) yielded a collection of 320 styryl dyes with very diverse spectral properties, and they were evaluated as amyloid probes without further purification. 

Several series of styryl-based dyes incorporating thia-crown ether moieties (e.g., II) have been prepared and smdied as selective optical sensors for heavy metal ions in aqueous solutions. 

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