Development of Pyrazolotriazole Magenta Coupler Using Intramolecular Hydrogen Bond For Higher Light Stability

摘要

A new type of lH-pyrazolo[5,l-c][l,2,4]triazole magenta couplers which produce dyes having high light stability was developed. The most peculiar characteristic to these couplers is that they have a ballast group that can form plural intramolecular hydrogen bonds in the forming dyes with an oxidized color developing agent. The conformation of the CD-3 azomethine dyes derived from these couplers were calculated by using Boltzmann Jump Method and the most stable structure was speculated. The calculation results showed that the ballast group would protect the dye nucleus by means of the intramolecular hydrogen bond in the most stable conformer. This steric protection is expected to prevent the reactive materials such as singlet oxygen (~1O_2) from attacking the dye, and as a result, to enhance the light stability of the dye. When the dye has a ballast group containing beta-alanine moiety, the steric protection is supposed to be particularly effective. It was demonstrated that the dyes possessing the plural intramolecular hydrogen bonds significantly enhance light stability. In order to prove this assumption, two types of CD-3 dyes were synthesized and their behaviors were investigated. One was the dye derived from the coupler containing a beta-alanine moiety and the other was the dye derived from the coupler not containing a beta-alanine moiety. The two types of dyes were analyzed by HPLC and 'HNMR. The result showed the intramolecular hydrogen bond was formed in the dye derived from the couplers containing beta-alanine moiety and its force was strongest. It was demonstrated that the intramolecular hydrogen bond is strongly related to enhancement of the light stability.