A new carbon–carbon bonded nanoporous polymer network was synthesized via efficient and catalyst free Knoevenagel-like condensation polymerization in near quantitative yields. The obtained polymer network, Covalent Organic Polymer – COP-100 possesses strong fluorescent properties and designed solubility in polar aprotic solvents, which shows promise for use as a metal-sensing material in solution. COP-100 exhibited high selectivity towards Fe²⁺ and Fe³⁺ in the presence of other common metal cations (Al³⁺, Ag⁺, Cd²⁺, Co²⁺, Cr³⁺, Cu²⁺, Hg²⁺, Mg²⁺, Mn²⁺, Na⁺, Ni²⁺, Zn²⁺) as the fluorescence of the polymer was significantly quenched even at very low concentrations. In the range from 2.5 × 10⁻⁶ to 2 × 10⁻⁴ M, a linear fluorescence emission response with equipment limited detection minimum of 2.13 × 10⁻⁷ M and 2.45 × 10⁻⁷ M for Fe²⁺ and Fe³⁺, respectively, was observed. These results suggest that COP-100 is a promising material as a selective fluorescence sensor for iron ions.