N-Phenylthiosemicarbazones (R1-R4) have been synthesized and characterized by various spectroscopic techniques. The sensors (R1-R4) exhibited highly selective and sensitive recognition toward Cu2+ and F- ions over other cations and anions via visual color change. Sensors showed a significant fluorescent enhancement toward Cu2+ in aqueous medium and found a sub-nanomolar detection limit with good quantum yield. R1 displayed high selectivity to Cu2+ over other interference ions with 89-fold fluorescence intensity enhancement upon the addition of 2 equiv. of Cu 2+. In addition, the turn-on fluorescent changes upon the addition of Cu2+, is also applied in cell imaging.