Impact of peripheral halogenation on the structure-property relationships of tetrathienoanthracene (TTA) derivatives: Synthesis, structural characterization, and theoretical studies

In this study, we report the design, synthesis, and comprehensive structural characterization of three novel tetrathienoanthracene (TTA) derivatives (8, 9, and 10) featuring an A-π-D-π-A molecular architecture. An efficient six-step synthetic route was developed, affording the target compounds in overall yields exceeding 20%. We investigated the impact of peripheral halogenation (fluorine vs. chlorine) on the molecular geometry, packing behavior, and optoelectronic properties. Spectroscopic analysis revealed broad absorption in the visible spectrum, with the chlorinated derivative (10) exhibiting a solution-state onset wavelength extending to 712 nm. Notably, upon solid-state film formation, the halogenated derivatives displayed significant bathochromic shifts (>90 nm), attributed to enhanced intermolecular aggregation and planarization of the π-conjugated backbone. Electrochemical measurements, corroborated by Density Functional Theory (DFT) calculations, confirmed that halogen introduction effectively modulates the frontier molecular orbitals, lowering HOMO/LUMO energy levels and narrowing the electrochemical band gap to 1.69 eV. Computational studies further elucidated the torsional profiles and conformational stability of the terminal groups, providing a theoretical basis for the observed structure-property relationships. These results underscore the efficacy of halogenation in fine-tuning the electronic structure and solid-state organization of TTA-based materials.