Principle of SYBR Green
SYBR Green I (SG) is an asymmetrical cyanine dye used as a nucleic acid stain in molecular biology.
This molecule is commonly used in qPCR to meassure the amount of double stranded DNA. The fluorescent dye SYBR Green I binds to the minor groove of the DNA double helix. In solution, the unbound dye exhibits very little fluorescence (left figure below), however, fluorescence is greatly enhanced upon DNA-binding (right figure below).
Although its common use I cannot figure out why SYBR green fluorescence more when bound to DNA.
*I first doubted whether I should have posted this on biology stackexchange due to its relevance in this field, however I think this question covers way more chemistry than biology.