Unsymmetrical cyanine dyes for high resolution nucleic acid melting analysis

An unsymmetrical cyanine dye having the Formula I

• wherein A is
• wherein
• X is O or S;
• R1, R2, R3, R4, R5, R6 and R7 are independently hydrogen, halogen, thiol, optionally substituted alkyl, optionally substituted alkoxy, optionally substituted alkenyl, optionally substituted polyalkenyl, optionally substituted alkynyl, optionally substituted polyalkynyl, optionally substituted thioalkyl, optionally substituted aminoalkyl, optionally substituted aryl, optionally substituted heteroaryl and optionally substituted arylalkyl;
• R1 and/or R2 carry one or more positive charges such that the sum of the positive charge(s) on R1 and R2 is 1, 2 or 3;
• and
• R3, and/or R4, and/or R5, and/or R6 and/or R7 carry one or more positive charges such that the sum of the positive charge(s) on R3, R4, R5, R6 and R7 is 1, 2 or 3.