prov:value
| - This Example illustrates the preparation, by the reaction Q+R???N shown in FIG. 3, of the dye Q in which R3 is a butyl group and R1, R2 and R4 are each a hydrogen atom, this being the dye of Formula I in which Q1 is a 2,6-bis(1,1-dimethylethyl)-4H-thiopyran-4-ylidene grouping, Q2 is a 4-[2,6-bis(1,1-dimethmethylethyl)-4H-thiopyrylium] grouping, R3 is a butyl group and R1, R2 and R4 are each a hydr
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