| CPC C09B 11/24 (2013.01) [C12Q 1/6818 (2013.01)] | 20 Claims |

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1. A compound which is a photoactivable fluorescent dye having the structural formula I:
![]() wherein:
n=0, 1, 2, 3;
X is selected from O, CRR′, SiRR′ and GeRR′, where R and R′ represent independently alkyl, cycloalkyl, alkenyl, alkynyl or aryl;
Y is H, SO3H or SO3M, with M being a positively charged counterion;
R1 is H, CO2H, C(O)NH-linker-CO2H, C(O)O-ligand, C(O)NH-ligand or C(O)NH-linker-ligand;
R2 is H, unsubstituted alkyl, substituted alkyl, unsubstituted cycloalkyl or substituted cycloalkyl;
R3 and R4 are independently H or F;
R5 is H, Me, CO2H, C(O)NH-linker-CO2H, C(O)O-ligand, C(O)NH-ligand or C(O)NH-linker-ligand;
wherein the ligand at each occurrence represents a reactive group or tag, capable to form a covalent or non-covalent bond or molecular complex with a target chemical entity or substance;
and wherein
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