BigDye® primers and terminators utilize single energy transfer molecules, which include an energy donor and acceptor dye connected by a highly efficient energy transfer linker. In the structure of the BigDye® molecule, the acceptor is a dichlororhodamine dye. Dichlororhodamine (dRhodamine) dyes are an improvement over conventional rhodamine dyes. dRhodamines are better spectrally resolved – there is significantly less spectral overlap at their maximum excitation wavelength, and their sequencing products show much reduced background noise. This results in a cleaner signal and greater base calling accuracy at longer read lengths. An energy transfer linker couples the donor fluorescein and acceptor dRhodamine dyes for efficient energy transfer in a single dye molecule. These brighter, cleaner dyes result in a sequencing chemistry suitable for most applications.