Study on New Cyan Dye Forming Compounds (II)

Indazole Derivatives (1)

Abstract

Five kinds of 3-substituted indazole (IND) derivatives were synthesized. Among them, only two kinds of IND derivs, 3-sulfonamidoindazole (IND-1) and 3-phosphoramidoindazole (IND-2), were able to couple with quinonediimine (QDI) at 7-position on indazole ring to form azomethine cyan dyes (IND-1-Dye and IND-2-Dye).
The absorption spectra of these dyes were measured in methanol and we found that both dyes were hypsochromically shifted in hue compared with conventional phenolic cyan dye (PH-Dye) and that they had more desirable spectral absorption characteristics with narrower half band width (W_1/2) and smaller unfavorable absorption peak at the region of 400-500 nm than PH-Dye.
The important factors for the coupling reactivity of IND-1 and IND-2 can be summarised as follows: 1) stabilization of possible 2H-indazole (quinonoid form) through intramolecular hydrogen bonding between 2-NH and 3-NHSO₂-(or 3-NHP0-), 2) the dissociation of 3-NHSO₂-(3-NHP0-), and 3) the migration of an anion charge from 3-N-SO₂-(3-N-PO-) to the carbon atom at the 7-position on the indazole ring. However, indazole is considered to be able to couple with QDI not only at 7- but also 5-position. The more study is required on determining the coupling position. The detailed study on this point is now in progress.