Heterocycle-substituted xanthene dyes

A compound of Formula 1a:

• wherein:
• X is O, S, or —C(CH3)2—;
• A is —OR1 or —NR1R1a;
• B is ═O or ═N+R4R4a;
• C is —OR4 or —NR4R4a;
• R1, R1a, R4, and R4a are each independently H or alkyl, unsubstituted or substituted with -L-SO3−, -L-PO32−, a water-soluble polymer, or with -L-Rx;
• or one or more pair of R1 and R1a or R4 and R4a together with the nitrogen to which they are attached form a saturated or unsaturated ring optionally substituted by any of -L-SO3−, -L-PO32− and -L-Rx;
• or at least one of R1, R1a, R4, or R4a is an enzyme substrate or a protecting group;
• R7 is a 5-membered monocyclic heteroaryl group, optionally substituted with one or more substituents selected independently from halogen, CO2−, CN, alkyl, alkenyl, alkoxy, alkylthio, alkylamino, dialkylamino, alkylaminocarbonyl, dialkylaminocarbonyl, alkylaminosulfonyl, dialkylaminosulfonyl, aminosulfonyl, aryl, heteroaryl, -L-PO32−, L-SO3−, and -L-Rx;
• R2, R3, R5, R6, R8, R9, are each independently H, halogen, CN, alkyl, alkenyl, alkoxy, aryl, heteroaryl, -L-PO32−, -L-SO3−, or -L-Rx;
• or one or more pair of R2 and R1a, R3 and R4a, R4 and R5, R5 and R6, R8 and R9, or R9 and R1, together with the atoms to which they are attached form one or more fused saturated or unsaturated rings that are optionally substituted by at least one halogen, CN, alkyl, alkenyl, alkoxy, alkylthio, alkylamino, dialkylamino, alkylaminocarbonyl, dialkylaminocarbonyl, alkylaminosulfonyl, dialkylaminosulfonyl, aminosulfonyl, aryl, heteroaryl, -L-PO32−, L-SO3−, or -L-Rx;
• Rx is a reactive group;
• L is a bond or (Q)n;
• each Q is independently NRd, S(O)t, O, C(═X), (C═X), substituted or unsubstituted alkyl, substituted or unsubstituted heteroalkyl, substituted or unsubstituted aryl, substituted or unsubstituted heteroaryl, substituted or unsubstituted cycloalkyl, or substituted or unsubstituted heterocycloalkyl, wherein t is 0-2, and no more than two NRd are adjacent and no two O are adjacent;
• n is 1-20;
• and
• each Rd is H, substituted or unsubstituted alkyl;
• wherein
• R7 is substituted with -L-Rx or at least one of R2 and R3 is -L-SO3−.