This article describes a new block copolymer (EG--AP, where and denote the degrees of polymerization) of poly(ethylene glycol) (PEG) and poly(1,4-(1--1,2,3-triazolylene)methylene) prepared by copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) polymerization of 3-azido-1-propyne (AP) in the presence of PEG carrying a propargyl moiety. The EG--AP samples are well soluble in polar organic solvents. Unexpectedly, we observed that solutions of EG--AP in ,-dimethylformamide emitted fluorescence. We systematically studied absorption and emission properties of the block copolymers. The experimental data have exhibited that AP block is an intrinsic fluorophore. Interestingly, the emission of EG--AP can be easily tuned from ultraviolet to green fluorescence by changing the excitation wavelength. This enables fine-tuning of its optical property without the need of changing the chromophore. Moreover, the block copolymers show a fluorescence response to metal ions (e.g., Cu). Our discoveries contribute to the fundamental understanding of the optical properties of dense triazole-based polymer and raise intriguing prospects for fabricating novel emissive triazole-based materials.