An iridium-based chemiluminescent compound of Formula II wherein in Formula I (a) and in Formula I (b), respectively and independently, each R1-R16 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 R17, wherein R17 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, 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, 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-R17 a substitution is present, the substituent in R1-R17 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 group, 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-R16 in Formula I (a) is -Q1-Y, wherein at least one of R13-R16 in Formula I (b) is Q2 wherein Q1 is a linker and each Q2 independently is a linker or a covalent bond, wherein (n) is an integer from 1 to 50 and wherein Y is a functional group.