A chemiluminescent acridinium compound having the following structure: wherein, R 1 is a C 1-35 alkyl, alkenyl, alkynyl or aralkyl group, each of which may contain up to 20 heteroatoms, or a sulfopropyl or sulfobutyl group, or R 1 is a group -R a -Z; R 2 and R 3 are independently selected from (i) hydrogen, (ii) an electron donating group selected from OR #, OH, SR #, SH, NH 2 and NR N R N, wherein R # and R N are independently selected at each occurrence and are selected from the group consisting of hydrogen, alkyl, alkenyl, alkynyl, aryl and aralkyl, each containing up to 20 heteroatoms, or (iii) a group - Z; Y and Y' are independently selected from R, -R a -Z, or -R a -L; where L is a derivatizable functional group comprising a leaving group for forming a conjugate with an analyte, analyte analog, or binding partner for an analyte; Z is a zwitterionic group of the form: X is independently selected at each occurrence from a bond, -CH 2 -, oxygen, sulfur, -NR N -, amide (-NR N -), carbamate (-NR N C O-), or urea (-NR N C NR N -); R' and R" are independently selected at each occurrence from C 1-35 alkyl, alkenyl, alkynyl, aryl, or aralkyl, each containing up to 20 heteroatoms, and a group R a -L; Z 1 is a group -R a -Z 2 where Z 2 is selected from carboxylate (-COO -), sulfonate (-SO 3 -), sulfate (-OSO 3 -), phosphate (-OP (O -)), or oxide (-O -); or, in the case where Z 2 is an oxide (-O -), R a may be absent; n is, independently selected at each occurrence, an integer between one and 12; and R is independently selected at each occurrence from C 1-35 alkyl, alkenyl, alkynyl, aryl, or aralkyl groups each containing up to 20 heteroatoms; R N is independently selected at each occurrence from hydrogen, C 1-35 alkyl, alkenyl, alkynyl, aryl, or aralkyl groups each containing up to 20 heteroatoms; and R a is a divalent radical selected from C 1-35 alkylene, alkenylene, alkynylene, arylene, or aralkylene group, each optionally containing up to 20 heteroatoms; with the proviso that at least one of R 1, R 2, R 3, Y and Y' comprises said zwitterionic group Z, wherein L is selected from the group consisting of: R 1 is a C 1-35 alkyl, alkenyl, alkynyl or aralkyl group, each of which may contain up to 20 heteroatoms, or a sulfopropyl or sulfobutyl group, or R 1 is a group -R a -Z; R 2 and R 3 are independently selected from (i) hydrogen, (ii) an electron donating group selected from OR #, OH, SR #, SH, NH 2 and NR N R N, wherein R # and R N are independently selected at each occurrence and are selected from the group consisting of hydrogen, alkyl, alkenyl, alkynyl, aryl and aralkyl, each containing up to 20 heteroatoms, or (iii) a group - Z; Y and Y' are independently selected from R, -R a -Z, or -R a -L; where L is a derivatizable functional group comprising a leaving group for forming a conjugate with an analyte, analyte analog, or binding partner for an analyte; Z is a zwitterionic group of the form: X is independently selected at each occurrence from a bond, -CH 2 -, oxygen, sulfur, -NR N -, amide (-NR N -), carbamate (-NR N C O-), or urea (-NR N C NR N -); R' and R" are independently selected at each occurrence from C 1-35 alkyl, alkenyl, alkynyl, aryl, or aralkyl, each containing up to 20 heteroatoms, and a group R a -L; Z 1 is a group -R a -Z 2 where Z 2 is selected from carboxylate (-COO -), sulfonate (-SO 3 -), sulfate (-OSO 3 -), phosphate (-OP (O -)), or oxide (-O -); or, in the case where Z 2 is an oxide (-O -), R a may be absent; n is, independently selected at each occurrence, an integer between one and 12; and R is independently selected at each occurrence from C 1-35 alkyl, alkenyl, alkynyl, aryl, or aralkyl groups each containing up to 20 heteroatoms; R N is independently selected at each occurrence from hydrogen, C 1-35 alkyl, alkenyl, alkynyl, aryl, or aralkyl groups each containing up to 20 heteroatoms; and R a is a divalent radical selected from C 1-35 alkylene, alkenylene, alkynylene, arylene, or aralkylene group, each optionally containing up to 20 heteroatoms; with the proviso that at least one of R 1, R 2, R 3, Y and Y' comprises said zwitterionic group Z, wherein L is selected from the group consisting of: X is independently selected at each occurrence from a bond, -CH 2 -, oxygen, sulfur, -NR N -, amide (-NR N -), carbamate (-NR N C O-), or urea (-NR N C NR N -); R' and R" are independently selected at each occurrence from C 1-35 alkyl, alkenyl, alkynyl, aryl, or aralkyl, each containing up to 20 heteroatoms, and a group R a -L; Z 1 is a group -R a -Z 2 where Z 2 is selected from carboxylate (-COO -), sulfonate (-SO 3 -), sulfate (-OSO 3 -), phosphate (-OP (O -)), or oxide (-O -); or, in the case where Z 2 is an oxide (-O -), R a may be absent; n is, independently selected at each occurrence, an integer between one and 12; and R is independently selected at each occurrence from C 1-35 alkyl, alkenyl, alkynyl, aryl, or aralkyl groups each containing up to 20 heteroatoms; R N is independently selected at each occurrence from hydrogen, C 1-35 alkyl, alkenyl, alkynyl, aryl, or aralkyl groups each containing up to 20 heteroatoms; and R a is a divalent radical selected from C 1-35 alkylene, alkenylene, alkynylene, arylene, or aralkylene group, each optionally containing up to 20 heteroatoms; with the proviso that at least one of R 1, R 2, R 3, Y and Y' comprises said zwitterionic group Z, wherein L is selected from the group consisting of: