Naturally occurring dyes are promising material as a pigment, because of their non-toxicity. Flavylium FV is a cationic dye having the 2-phenylbenzopyrylium skeleton, which is the same as those of natural anthocyanin dyes. Therefore, the impact of FV on the environment is expected to be small, compared with other synthetic dyes. In addition, the flavylium derivatives can be synthesized easily by the aldol condensation of salicylaldehydes and acetophenones. However, the stability of FV is known

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... o be poor FV easily undergoes transformation to a colorless 2-hydroxychalcone under slightly basic or heated conditions 1-6 . As shown in , the decoloration process starts by the hydration of FV caused by the attack of water or hydroxyl ion to give a colorless hemiacetal, followed by the conversion to the 2hydroxychalcone derivatives 7 . If the stability of FV can be enhanced, we expect to be able to use FV as an environmentally friendly coloring material. We have previously reported that FV can be stabilized by complexation with acidified clay, montmorillonite K10 8 . FV molecules are successfully intercalated into the interlayer of K10. The causes of the stabilization have been thought to be as follows 1 the electrostatic Yoshiumi KOHNO , † , Ryo HOSHINO , Shuji IKOMA , Masashi SHIBATA , Ryoka MATSUSHIMA , Yasumasa TOMITA , Yasuhisa MAEDA and Kenkichiro KOBAYASHI We have enhanced the stability of a flavylium dye, a model compound of a natural anthocyanin dye, by the incorporation into the interlayer of a natural clay, bentonite. The composite of the flavylium and the bentonite shows excellent stability under increased temperature up to 353 K or alkaline environment pH 9 compared to the original flavylium dyes. This material can be candidate of an environmentally friendly coloring material. Increased amount of dye causes a muddy color due to the formation of dye aggregate. Samples with brilliant color can be obtained with the loading amount less than 0.25 mmol dye per g-clay.