The emissive π-conjugated polymers are attractive candidates as sensory materials for environmentally and biologically relevant species. In this work, we report design and synthesis of carbazole-thiophene based A-alt-B type efficient fluorescent π-conjugated copolymer probe with diketopyrrollopyrrole units through Pd(II)-catalyzed Sonogashira polymerization from the respective monomers. The well-defined and soluble π-conjugated polymer has been characterized by multinuclear NMR spectra as well as tetradetector GPC studies, showing molecular weight (M_w) of 33.1 kDa. The emissive π-conjugated macromolecular probe consisting of the carbazole-thiophene backbone with diketopyrrolopyrrole (P1) anchoring unit shows selectivity toward Fe³⁺ ions inducing quenching of the fluorescence by ca. 72%. More interestingly, the resulting P1·Fe³⁺ metallopolymer exhibits high sensitivity and selectivity toward adenosine 5′-triphosphate (ATP) over the other representative pyrophosphate anions. Most importantly, the probe discriminates it from adenosine 5′-diphosphate (ADP) and adenosine 5′-monophosphate (AMP), presumably due to the much stronger electrostatic interaction between polymer and ATP than the others. To understand the sensing mechanism, the detailed photophysical and sensing studies have been carried out to understand the insight of metallopolymer-ATP interaction, which is responsible for selective fluorescence enhancing of P1·Fe³⁺ metallopolymer. The limit of detection of the metallopolymer probe towards ATP was found to be in the range of 7.92 × 10⁻⁷ M (365 ppb) with a high association constant in the order of 1.96 × 10⁵ M⁻¹. FLIM analysis and the time-resolved fluorescence anisotropy study have also been carried out to investigate molecular interaction between P1·Fe³⁺ metallopolymer and ATP.