Study on the ground-state to excited-state charge characteristics of bipolar and n-type bisisoindigo-based D-A conjugated polymers

Purpose Electronic excitation and charge transfer processes are fundamentally interconnected, critically determining the optoelectronic performance of organic semiconductors. The purpose of this study is to systematically examine donor–acceptor (D-A) conjugated polymers at the molecular level, with particular focus on elucidating charge distribution patterns and transition mechanisms to establish advanced design principles for these materials. Design/methodology/approach A series of bipolar and n-type bisisoindigo (BIID)-based D-A conjugated polymers were investigated from a molecular perspective using density functional theory and time-dependent density functional theory methods. The ground and excited state characteristics of these polymers were analyzed to correlate molecular structures with electronic properties. Findings This study demonstrates that aza-incorporation and fluoro-substitution have relatively minor effects on the electronic structure, with the latter causing only a slight increase in n-p* transitions. In marked contrast, oxa-incorporation shows substantial impact by significantly expanding electron hole distribution in the vinyl region. This modification effectively establishes a p-electron bridge between receptor units while simultaneously enhancing both charge transition density and electron transfer between structural fragments. Originality/value This investigation introduces a methodologically significant approach for the expedited design and rigorous screening of high-performance, air-stable n-type D-A conjugated polymers and organic electronic devices.