Display omitted •New fragmentation-based approach for evaluating the intra-chain excitonic coupling.•Frenkel exciton model can nicely reproduce full TDDFT calculations in weakly coupled systems.•Description for strongly coupled system require the inclusion of higher excited states in fragments. For computing the intra-chain excitonic couplings in polymeric systems, here we propose a new fragmentation approach. A comparison for the energetic and spatial properties of the low-lying excited states in PPV between our scheme and full quantum chemical calculations, reveals that our scheme can nicely reproduce full quantum chemical results in weakly coupled systems. Further wavefunction analysis indicate that improved description for strongly coupled system can be achieved by the inclusion of the higher excited states within each fragments. Our proposed scheme is helpful for building the bridge linking the phenomenological descriptions of excitons and microscopic modeling for realistic polymers.