The present invention relates to dye compounds represented by Formulae I and II, which are described in the specification. The dye compounds of the present invention have markedly improved quantum yields and emit strong fluorescence compared to existing cyanine dyes. Due to these advantages, the dye compounds of the present invention can find applications in various fields, for example, as probes for various biological systems where optical imaging is required. Particularly, the dye compounds of the present invention can be used as mitotrackers capable of labeling and tracking mitochondria. Therefore, the dye compounds of the present invention can be used to quantitatively image mitochondria in live tissues and cells. Furthermore, the dye compounds of the present invention can be applied as pH probes for measuring the pH of live cells.
