Fluorescent dyes containing fused tetracyclic bis-boron heterocycle and uses in sequencing

A compound of Formula (I):

• a salt or a mesomeric form thereof, wherein each of R1, R2, R3, R6, R7 and R8 is independently H, unsubstituted or substituted C1-C6 alkyl, C1-C6 alkoxy, unsubstituted or substituted C2-C6 alkenyl, unsubstituted or substituted C2-C6 alkynyl, C1-C6 haloalkyl, C1-C6 haloalkoxy, C1-C6 hydroxyalkyl, (C1-C6 alkoxy)(C1-C6 alkyl), unsubstituted or substituted amino, halo, cyano, carboxyl, hydroxy, nitro, sulfonyl, sulfino, sulfo, sulfonate, S-sulfonamido, N-sulfonamido, —C(═O)NR9 R10, —X—R11, unsubstituted or substituted C3-C10carbocyclyl, unsubstituted or substituted C6-C10 aryl, unsubstituted or substituted 5 to 10 membered heteroaryl, or unsubstituted or substituted 3 to 10 membered heterocyclyl;
• each of R4 and R5 is independently H, unsubstituted or substituted C1-C6 alkyl, unsubstituted or substituted C3-C10 carbocyclyl, unsubstituted or substituted C6-C10 aryl, unsubstituted or substituted 5 to 10 membered heteroaryl, or unsubstituted or substituted 3 to 10 membered heterocyclyl;
• each of R9 and R10 is independently H, or unsubstituted or substituted C1-C6 alkyl;
• X is —O—, —S—, CH═CH— or —C≡C—;
• each of R11 is independently unsubstituted or substituted C3-C10 carbocyclyl, unsubstituted or substituted C6-C10 aryl, unsubstituted or substituted 5 to 10 membered heteroaryl, or unsubstituted or substituted 3 to 10 membered heterocyclyl;
• each of Ra, Rb, Rc and Rd is independently halo, cyano, unsubstituted C1-C6 alkyl, C1-C6 haloalkyl, C1-C6 alkoxy, C1-C6 haloalkoxy, unsubstituted or substituted C6-C10 aryl, unsubstituted or substituted C6-C10 aryloxy, or —OC(═O)R12;
• R12 is unsubstituted or substituted C1-C6 alkyl, unsubstituted or substituted C2-C6 alkenyl, unsubstituted or substituted C6-C10 aryl, or unsubstituted or substituted 5 to 10 membered heteroaryl;
• alternatively, when both Ra and Rb are —OC(═O)R12, the two R12 together with the atoms to which they are attached form an unsubstituted or substituted 6 to 10 membered heterocyclyl;
• alternatively, when both Rc and Rd are —OC(═O)R12, the two R12 together with the atoms to which they are attached form an unsubstituted or substituted 6 to 10 membered heterocyclyl;
• and
• provided that at least one of R1, R2, R3, R4, R5, R6, R7 and R8 comprises a carboxyl group.