An iridium-based chemiluminescent compound of Formula I wherein each R1-R20 independently is hydrogen, halide, cyano- or nitro-group, amino, substituted amino, alkylamino, substituted alkylamino, arylamino, substituted arylamino, alkylammonium, substituted alkylammonium, carboxy, carboxylate, carboxylic acid ester, carbamoyl, hydroxy, substituted or unsubstituted alkyloxy, substituted or unsubstituted aryloxy, sulfanyl, substituted or unsubstituted alkylsulfonyl, substituted or unsubstituted arylsulfonyl, sulfo, sulfino, sulfeno, sulfonate, sulfinate, sulfenate, sulfamoyl, sulfoxide, phosphono, hydroxyphosphinoyl, hydroxy-alkyl-phosphinoyl, phosphonate, phosphinate or R21, wherein R21 is aryl, substituted aryl, alkyl, substituted alkyl, branched alkyl, substituted branched alkyl, arylalkyl, substituted arylalkyl, alkylaryl, substituted alkylaryl, alkenyl, substituted alkenyl, alkynyl, substituted alkynyl, amino-alkyl, substituted amino-alkyl, amino-alkoxy, substituted amino-alkoxy, amino-aryl, substituted amino-aryl, amino-aryloxy, substituted amino-aryloxy, wherein within R1-R12, or/and within R13-R16 or/and within R17-R20, respectively, two adjacent Rs can form an aromatic ring or a substituted aromatic ring, wherein the substituent is selected from hydrogen, alkyl, substituted alkyl, halide, cyano- or nitro-group, a hydrophilic group, like amino, substituted amino, alkylamino, substituted alkylamino, alkylammonium, substituted alkylammonium, carboxy, carboxylate, carboxylic acid ester, carbamoyl, hydroxy, substituted or unsubstituted alkyloxy, substituted or unsubstituted aryloxy, sulfanyl, substituted or unsubstituted alkylsulfonyl, substituted or unsubstituted arylsulfonyl, sulfo, sulfino, sulfeno, sulfonate, sulfinate, sulfenate, sulfamoyl, sulfoxide, phosphono, hydroxyphosphinoyl, hydroxyl-alkyl-phosphinoyl, phosphonate, phosphinate or, wherein within R1-R12, or/and within R13-R16, or/and within R17-R20, respectively, two adjacent Rs can form an aliphatic ring or a substituted aliphatic ring, wherein the substituent is selected from hydrogen, alkyl, substituted alkyl, halide, cyano- or nitro-group, a hydrophilic group, like amino, substituted amino, alkylamino, substituted alkylamino, alkylammonium, substituted alkylammonium, carboxy, carboxylate, carboxylic acid ester, carbamoyl, hydroxy, substituted or unsubstituted alkyloxy, substituted or unsubstituted aryloxy, sulfanyl, substituted or unsubstituted alkylsulfonyl, substituted or unsubstituted arylsulfonyl, sulfo, sulfino, sulfeno, sulfonate, sulfinate, sulfenate, sulfamoyl, sulfoxide, phosphono, hydroxyphosphinoyl, hydroxyl-alkyl-phosphinoyl, phosphonate, phosphinate, wherein, if in any of R1-R21 a substitution is present, the substituent in R1-R21 is each independently selected from a halide, cyano- or nitro-group, a hydrophilic group, like an amino, alkylamino, alkylammonium, carboxy, carboxylate, carboxylic acid ester, carbamoyl, hydroxy, alkyloxy, arylalkyloxy, aryloxy, alkylaryloxy, polyethylenoxy, polypropylenoxy, sulfanyl, alkylsulfonyl, arylsulfonyl, sulfo, sulfino, sulfeno, sulfonate, sulfinate, sulfenate, sulfamoyl, sulfoxide, phosphono, hydroxyphosphinoyl, hydroxyl-alkyl-phosphinoyl, phosphonate, phosphinate, wherein alkyl as used herein is a linear or branched alkyl chain with a length of 1-20 carbon atoms or a heteroalkyl chain with the length of 1-20 atoms comprising 1-4 heteroatoms selected from O, N, P, and S, wherein aryl is a 5, 6, or 7 member aryl ring system, or a 5, 6, or 7 member heteroaryl ring system comprising 1-3 heteroatoms selected from O, S and N, wherein at least one of R13-R20 is -Q-Z, wherein Q is a linker or a covalent bond, and wherein Z is a functional group and, wherein at least one of X and Y is N and the other X or Y independently is N or C.