A polymer based fluorescence “turn-on” chemosensor is demonstrated with high sensitivity and selectivity towards Fe²⁺ cations. This system is an inorganic/organic hybrid system in which Cu²⁺ is coordinated at the receptor site of a conjugated polymer sensor. The unique quenching behavior of the Cu²⁺ towards this conjugated polymer was used to lower the initial fluorescence intensity of the sensory system. This results a highly sensitive and also selective sensory system towards Fe²⁺ as compared to other related divalent transition metal cations in solution.