Poly(arylene ether nitrile)s (PAENs) appended with Zn(II)-porphyrin in varied molar percentages (5% and 10%) are developed as dual colorimetric and fluorometric sensors for highly sensitive and selective cyanide (CN−) detection. The materials, DP-5%PAEN@Zn and DP-10%PAEN@Zn, exhibit significant Soret band shifts at 420 ± 2 nm, accompanied by the appearance of a new absorption band at 436 ± 2 nm, indicating strong CN− binding with high association constants of 1.3 × 10⁴ M−¹ and 2.3 × 10⁴ M−¹, respectively. A prominent color change from purple to green allowed for naked eye detection. Spectrofluorimetric studies revealed turn-off fluorescence with Stern-Volmer constants (Ksv) of 99.85 × 103 M−¹ for DP-5%PAEN@Zn and 121.08 × 103 M−¹ for DP-10%PAEN@Zn, achieving limit of detection (LOD) of 0.177 and 0.099 ppb, respectively. DP-10%PAEN@Zn demonstrated excellent sensitivity and selectivity toward CN−, and also reusability, as it remained functional after ten TFA treatment cycles. The mechanistic investigation, supported by photophysical, electrochemical, and DFT analyses, revealed a photoinduced electron transfer process via static quenching. Material stability is confirmed through photodegradability, prolonged time, temperature, and humidity testing. Prototype test kits are developed for real-time visual CN− detection in remote and environmental samples (tap, lake, sewage, and soil). Additionally, a smartphone-based color recognition assay is implemented for qualitative and quantitative analysis.