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Abstract

Amid the accelerating global energy transition and the deepening emphasis on sustainable development, organic semiconductors have attracted increasing attention as promising candidates for next-generation optoelectronic and energy devices, owing to their highly tunable molecular structures, low-cost processing, and excellent mechanical flexibility. A thorough understanding of the electronic structures of these molecules and their charge-transfer mechanism is crucial for guiding molecular design, optimizing device performance, and predicting functional properties. In particular, quantum chemical calculations provide useful quantitative insights into the excited-state behavior and charge mobility prediction, offering theoretical support for the design and optimization of organic semiconductor materials. In this work, the photoexcitation processes of triphenylamine (TPA) and its dimethylmethylene-bridged derivative (DTPA) in chloroform solution were first explored. Unlike conventional cyclization reactions, which often produce significant carbazole by-products, the TPA derivatives act as electron donors transferring electrons to the electron-accepting chloroform, inducing dimer formation. The absorption spectra obtained from quantum chemical calculations agree closely with experimental measurements, validating the computational model and providing a quantitative basis for understanding electron transfer in solution. Subsequently, the carrier mobilities of the organic molecules were calculated by combining Marcus–Hush theory with quantum chemical methods. By introducing a projection function based on the intermolecular polar angle (γ) and azimuthal angle (θ), the relative mobilities of different dimer types along specific directions were quantified, allowing precise characterization of anisotropic charge transport. Using this approach, the electronic structures and spatial charge transport properties of halogenated N-heteroacene derivatives 4Br-TIPS-TAP and 4I-TIPS-TAP were investigated. Both molecules exhibit typical n-type behavior, consistent with previous reports, highlighting the significant effects of molecular design and halogen substitution on crystal packing and transport properties. Finally, the three-dimensional anisotropic charge transport of singlet fission (SF)–active diketopyrrolonaph- thyridinedione derivatives, namely DPND and DPND6, was examined. The calculations indicate that the unsub- stituted DPND predominantly favors p-type transport, whereas the side-chain–modified DPND6 exhibits n-type characteristics. This result demonstrates that side-chain–induced changes in crystal packing can reverse the domi- nant carrier type, providing clear theoretical guidance for tuning charge transport through molecular design. These findings not only deepen the understanding of structure–property relationships in organic semiconductors but also offer feasible strategies for applying singlet fission materials in efficient optoelectronic devices.