ABSTRACTTwo new conjugated polymers poly{3‐({4‐[(2‐hydrazino‐2‐oxoethyl)(methyl)amino]cyclohexylidene}methyl)thiophene}(P1) and poly{3‐({4‐[(3‐hydrazino‐3‐oxopropyl)(methyl)amino]cyclohexylidene}methyl)thiophene}(P2) were synthesized, and their optical properties were investigated. P1 exhibited excellent selectivity toward Cu2+ ions in 50% water solution, the fluorescence color of P1 changed distinctly from greenyellow to colorless in the presence of Cu2+ under UV‐light, while introduction of other metal ions could not induce such significant variation. Moreover, highly sensitive detection of Cu2+ ions was demonstrated in 90% water solution. Its high metal‐chelating capability allowed Cu2+ recognition with a detection limit of 3.2 × 10−10 M. These results indicated that this kind of nonionic polymer containing multidentate ligand could be used as a highly selective and sensitive chemosensor for Cu2+ detection. The proposed binding mode of P1 with Cu2+ was supported by DFT calculation using Gaussian 03. Unlike P1, P2 showed no obvious fluorescent change in the presence of various metal ions due to its space steric hindrance resulted from N/O distribution on the side chain of P2. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42440.