Compounds having particular interest as labels and various novel uses in diagnostics and therapeutics are provided which have structure (1) ##STR1##

wherein R¹ is a binding partner, a linker or H;

• a and b are 0 or 1, provided that the total of a and b is 0 or 1;
• A is N or C;
• X is S, O, —C(O)—, NH or NCH₂R⁶;
• Y is —C(O)—;
• Z is taken together with A to form an aryl or heteroaryl ring structure comprising 5 or 6 ring atoms wherein the heteroaryl ring comprises a single O ring heteroatom, a single N ring heteroatom, a single S ring heteroatom, a single O and a single N ring heteroatom separated by a carbon atom, a single S and a single N ring heteroatom separated by a carbon atom, 2 N ring heteroatoms separated by a carbon atom, or 3 N ring heteroatoms at least two of which are separated by a carbon atom, and wherein the aryl or heteroaryl ring carbon atoms are unsubstituted with other than H or at least 1 nonbridging ring carbon atom is substituted with R⁶ or O;
• R⁶ is independently H, C₁-C₆ alkyl, C₂-C₆ alkenyl, C₂-C₆ alkynyl, NO₂, N(R³)₂, CN or halo, or an R⁶ is taken together with an adjacent R⁶ to complete a ring containing 5 or 6 ring atoms;
• R³ is a protecting group or H; and tautomers, solvates and salts thereof; and provided that where a is 0, b is 1, and R¹ is ##STR2##
• in which D² is independently hydroxyl, blocked hydroxyl, mono, di or triphosphate, or an oligodeoxyribonucleotide otherwise containing only the bases A, G, T and C; and
• D³ is H or OH;

  then Z is not unsubstituted phenyl.

Also provided are novel intermediates and methods for the preparation and use of the structure (1) compounds.