A First-Principles Study of the Structure and Electronic Properties of Bridged Cofacial Phenylene–Vinylene Oligomers

Interchain electronic interactions significantly influence the performance of organic photovoltaics. These interactions are affected by structural disorder in the polymer film, complicating the isolation and quantification of effects and thereby impacting the study of structure-property relationships for the optimization of the materials. In this study, we employed unbridged stilbene (1PV) and oligo(p-phenylenevinylene) ( o -PV) dimers, as well as the rigidly bridged xanthene- or dibenzofuran-bridged cofacial phenylene-vinylene oligomers, as well-defined molecular models to extract and quantify such effects. A systematic first-principles study of the structural, electronic, and optical properties of these systems was performed using density functional theory (DFT) and time-dependent DFT in the gas phase and in dichloromethane solution. The band (HOMO-LUMO) gaps and UV-visible spectra obtained from the calculation revealed a red-shifted band and effective conjugation extension arising from the backbone planarization, and a higher energy blue-shifted band arising from excitonic coupling between adjacent π-systems. Significant red shifts were observed in dibenzofuran-bridged systems arising from enhanced intrachain planarity and open cofacial geometries. In contrast, the xanthene-bridged system demonstrated a strong π–π overlap, leading to increased orbital delocalization, more pronounced excitonic splitting, and reduced HOMO–LUMO gaps due to its smaller bite angles and tighter cofacial alignment. The study showed that solvent stabilization effectively suppresses intrachain twisting and promotes backbone planarity.