Stability and tinctorial strength of black leuco-colorants as viewed from the crystal structure of a phenolic developer
Abstract:Certain leuco dyestuffs are known to exhibit a brilliant color by reaction with a phenolic developer. 2-[(4-hydroxyphenyl) sulfonyl]-phenol (BPS) is a well-known developer for black leuco dyes such as 6′-(diethylamino)-3′-methyl-2′-(phenylamino)-spiro[isobenzofuran-1(3H), 9′-[9H]-xanthen)-3-one (ODB) in thermosensitive papers. Although BPS is a small molecule (molecular weight: about 250), it is thermally stable as characterized by a high melting point of about 184 °C. Furthermore, the stability of BPS is also extended to the 1:1 “leuco/developer” system. In this connection, structure analysis of BPS has been carried out in order to elucidate the stability of BPS itself as well as its leuco/developer system. Then, we found that one BPS molecule is hydrogen-bonded to four different neighboring ones, forming an OH...O two-dimensional hydrogen-bond network. This ensures a high thermal stability of BPS. On the other hand, in the ODB/BPS system, only one of the four hydrogen bonds in BPS is used for the formation of the 1:1 ODB/BPS colorant while the remaining three hydrogen bonds keep the network. As for the tinctorial strength in spin-coated ODB/BPS, the color intensity is found to be limited to about 70% of the maximum available value. This is because there is a fraction of ODB molecules, whose lactone ring is still closed owing to the steric hindrance.
Document Type: Research Article
Publication date: January 1, 2010
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