We have synthesized a fluorescent base analogue, 2-aminothieno[3,4-d]pyrimidine based G-mimic deoxyribonucleoside, 2′-OMe-^thG, and investigated its photophysical properties and DNA incorporation. The 2′ methoxy group of 2′-OMe-^thG effectively induces the Z-form DNA. Finally we have constructed a visible nanothermometer based on the B–Z transition of DNA using 2′-OMe-^thG.