An iridium-based chemiluminescent compound of Formula I wherein R1-R16 is hydrogen, halide, cyano- or nitro-group, amino, alkylamino, substituted alkylamino, arylamino, substituted arylamino, alkylammonium, substituted alkylammonium, carboxy, carboxylic acid ester, carbamoyl, hydroxy, substituated or unsubstituated alkyloxy, substituted or unsubstituted aryloxy, sulfanyl, alkylsulfonyl, arylsulfonyl, sulfo, sulfino, sulfeno, sulfonamide, sulfoxide, sulfodioxide, 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, wherein the substituent is selected from hydrogen, halide, cyano- or nitro-group, a hydrophilic group, like amino, alkylamino, substituted alkylamino, alkylammonium, substituted alkylammonium, carboxy, carboxylic acid ester, carbamoyl, hydroxy, substituted or unsubstituated alkyloxy, substituted or unsubstituted aryloxy, sulfanyl, alkylsulfonyl, arylsulfonyl, sulfo, sulfino, sulfeno, sulfonamide, sulfoxide, sulfodioxide, phosphonate, phosphinate or, 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, halide, cyano- or nitro-group, a hydrophilic group, like amino, alkylamino, substituted alkylamino, alkylammonium, substituted alkylammonium, carboxy, carboxylic acid ester, carbamoyl, hydroxy, substituted or unsubstituted alkyloxy, substituted or unsubstituted aryloxy, sulfanyl, alkylsulfonyl, arylsulfonyl, sulfo, sulfino, sulfeno, sulfonamide, sulfoxide, sulfodioxide, 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, halide, cyano- or nitro-group, a hydrophilic group, like amino, alkylamino, substituted alkylamino, alkylammonium, substituted alkylammonium, carboxy, carboxylic acid ester, carbamoyl, hydroxy, substituted or unsubstituted alkyloxy, substituted or unsubstituted aryloxy, sulfanyl, alkylsulfonyl, arylsulfonyl, sulfo, sulfino, sulfeno, sulfonamide, sulfoxide, sulfodioxide, phosphonate, phosphinate and wherein at least one of R13-R16 is -Q-Y, wherein Q represents a linker and Y is a functional group and, wherein the functional group Y is selected from the group consisting of carboxylic acid, N-hydroxysuccinimide ester, amino group, halogen, sulfhydryl, maleimido, alkynyl, azide and phosphoramidite. wherein R1-R16 is hydrogen, halide, cyano- or nitro-group, amino, alkylamino, substituted alkylamino, arylamino, substituted arylamino, alkylammonium, substituted alkylammonium, carboxy, carboxylic acid ester, carbamoyl, hydroxy, substituated or unsubstituated alkyloxy, substituted or unsubstituted aryloxy, sulfanyl, alkylsulfonyl, arylsulfonyl, sulfo, sulfino, sulfeno, sulfonamide, sulfoxide, sulfodioxide, 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, wherein the substituent is selected from hydrogen, halide, cyano- or nitro-group, a hydrophilic group, like amino, alkylamino, substituted alkylamino, alkylammonium, substituted alkylammonium, carboxy, carboxylic acid ester, carbamoyl, hydroxy, substituted or unsubstituated alkyloxy, substituted or unsubstituted aryloxy, sulfanyl, alkylsulfonyl, arylsulfonyl, sulfo, sulfino, sulfeno, sulfonamide, sulfoxide, sulfodioxide, phosphonate, phosphinate or, 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, halide, cyano- or nitro-group, a hydrophilic group, like amino, alkylamino, substituted alkylamino, alkylammonium, substituted alkylammonium, carboxy, carboxylic acid ester, carbamoyl, hydroxy, substituted or unsubstituted alkyloxy, substituted or unsubstituted aryloxy, sulfanyl, alkylsulfonyl, arylsulfonyl, sulfo, sulfino, sulfeno, sulfonamide, sulfoxide, sulfodioxide, 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, halide, cyano- or nitro-group, a hydrophilic group, like amino, alkylamino, substituted alkylamino, alkylammonium, substituted alkylammonium, carboxy, carboxylic acid ester, carbamoyl, hydroxy, substituted or unsubstituted alkyloxy, substituted or unsubstituted aryloxy, sulfanyl, alkylsulfonyl, arylsulfonyl, sulfo, sulfino, sulfeno, sulfonamide, sulfoxide, sulfodioxide, phosphonate, phosphinate and wherein at least one of R13-R16 is -Q-Y, wherein Q represents a linker and Y is a functional group and, wherein the functional group Y is selected from the group consisting of carboxylic acid, N-hydroxysuccinimide ester, amino group, halogen, sulfhydryl, maleimido, alkynyl, azide and phosphoramidite.