| 摘要 |
A chromogenic pyrazine compound of formula: <CHEM> wherein X<1> and X<2>, which may be the same or different, are each selected from hydrogen, alkyl, optionally substituted alkyl, alkoxy, carboxyalkyl, optionally substituted aryl, optionally substituted heteroaromatic, optionally substituted aralkyl or dialkylamino, provided that both X<1> and X<2> are not both hydrogen at the same time; and A<1> and A<2>, which may be the same or different, are each: (i) a heterocyclic ring system having an aryl group annellated through a conjugated nitrogen linkage; or (ii) a homocyclic aryl group having a substituent -NR1R2 wherein R1 and R2 are separately hydrogen or an optionally substituted alkyl, aryl or aralkyl group or both R1 and R2 together with the nitrogen atom to which they are joined form a nitrogen-linked ring, provided that R1 and R2 are not both hydrogen at the same time. |
