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Color compensation technology made it possible to enhance the image quality of plasma panel display (PDP) devices. We examined the chemicals used in color compensation filters for PDP units in this study. Neon excitation during the plasma discharge causes orange light with an emission wavelength of 585 nm to be emitted from PDP devices. 1 This emitted orange light is mainly responsible for the degradation of color purity in PDP devices. 2 We synthesized three types of closed chain trimethine cyanines to attenuate unwanted spectral emissions having a wavelength 585 nm. Their common uses in PDP are near infrared absorbance filter. In this study, cyanines have been applied to neon orange light absorbing filter. By varying the number of carbons in the methine bridge of cyanine compound or by modifying the cyanine ring structure, 3,4 it is possible to synthesize cyanine structure absorbing particular wavelength and solvent solubility. A simple closed chain trimethine cyanine chromophore was synthesized by the condensation of 3-ethyl-2,4-dimethyl- pyrrole (kryptopyrrole) and TMOP with perchloric acid as shown in Scheme 1. Cyanine 1 was continuously synthesized using microchannel mixer and an extension tube. Kryptopyrrole was fed into one side of the microchannel mixer and the other reactants were fed into the other side. The reactants were mixed at the microchannel mixer and the reaction was carried out in the extension tube by heating at 60 o C. The microchannel mixer was operated at room temperature to avoid clogging it with precipitated solid particles. The volume of the extension tube was 10 mL, causing the retention time to vary from 0.37 s to 1.6 s depending on the total flow rate used in the experi- ment. We observed that a retention time of 0.37 s was sufficient to convert all reactants into product. A higher mass flow rate resulted in a shorter reactant retention time, thereby reducing the formation of byproducts. Cyanine 1 was produced with a yield of 95% and was 99.5% pure and dissolved in 2-butanone had a sharp absorption band at 580 nm with a half bandwidth of 36 nm. In comparison, azo or anthraquinone compounds typically had bandwidths of over 100 nm. 5 The width of the absorption band is dependent upon how closely the molecular structure in the first excited state resembles that in the ground state. The long conjugated chain structure of 1 was accompanied by a corresponding decrease in bandwidth. 6 The molar absorptivity of 1 was measured as 136,130 M -1 cm -1 . We synthesized a closed chain trimethine cyanine structure using 1-butyl-3-acetyl-2,4-dimethylpyrrole and 1,1,3,3-tetra- methoxypropane in the presence of perchloric acid as shown in Scheme 2. For the first step, several basic reagents were tested to generate a pyrrolyl anion for the alkylation of the nucleus in 3-acetyl-2,4-dimethylpyrrole with 1-bromobutane. Alkylation in the presence of potassium hydroxide in dimethyl sulfoxide gave 1-butyl-3-actyl-2,4-dimethylpyrrole with a 75 % yield. Other strong basic reagents such as potassium hydroxide in a solution of sodium amide or aqueous potassium hydroxide (50%) with tetrabutylammonium bromide in dichloromethane were also tested and delivered yields of 50% and 48%, respec- tively. Alkylation with sodium hydride in dimethyl sulfoxide increased the yield to 95%. The strong base, sodium hydride, reacts with dimethyl sulfoxide to produce dimsyl ions, which can effectively remove protons from the nucleus in 3-acetyl-2,4- dimethylpyrrole, thereby resulting in a more efficient alkylation with 1-bromobutane. The experimental result showed that 2 was obtained with a 70% yield and 98% purity. Some product loss took place during the washing and solid recovery steps. Cyanine 2 dissolved in 2-butanone had a maximum absorption at 580 nm with a half bandwidth of 39 nm. The molar absorp- tivity of 2 in 2-butanone was 32,303 M -1 cm -1 .

Flow Synthesis of Cyanine Dyes for Absorbing Orange Light from the Neon Gas Discharge