Amplifying polarity contrast in D‑π₁‑π₂‑A dyes: Heterocyclic replacement combined with cyano modification for...

Three novel D‑π₁‑π₂‑A organic dyes with polyheterocyclic π₂‑bridges and cyano‑modified acceptors were designed to amplify the polarity contrast between the terminal groups. Density functional theory (DFT) calculations were used to characterize the energy levels, absorption spectra, and intramolecular charge transfer (ICT) characteristics, with a focus on the regulatory effects of different electron‑withdrawing substituents on electron injection, dye regeneration, and charge recombination at the dye@TiO₂ interface. Simulation results indicate that SGT-149-3 exhibits the best photovoltaic performance, which can be attributed to two key structural optimizations: the replacement of the π₂-bridge with dithienothiophene and the rational modification of the acceptor with cyano group. The narrow energy gap leads to a significant redshift of 112.21 nm in the absorption spectrum compared to the reference dye SGT-149. The enhanced ICT effect improves the separation efficiency of photogenerated carriers, while stronger covalent interactions with TiO₂ substrates and prolonged fluorescence lifetime suppress charge recombination. The short-circuit current density and photoelectric conversion efficiency of SGT-149-3 reach 28.53 mA/cm² and 25.831%. Such exceptional photovoltaic parameters validate the latent application in photovoltaic devices. This work reveals the structure-property relationship between π-bridge engineering and acceptor modification, providing guidance for the rational design of high-efficiency dye-sensitized solar cells (DSSCs) sensitizers.

The ground-state geometries of all dye molecules were optimized at the B3LYP/6-311 g(d,p) level of DFT. The excited-state properties were calculated using the CAM-B3LYP/6-311 g(d,p) level of TD-DFT. For the dye@TiO₂ and dye@I systems, the 6-311 g(d,p) basis set was used for light atoms (C, H, O, N, S), while the LANL2TZ(f) pseudopotential basis set was applied to Ti and I atoms. The geometries of these complexes were optimized at the B3LYP level. All the simulations were conducted in THF solution using the SMD solvent model. This study employed the Gaussian 16 software package as the core computational tool. Multiwfn_3.8 was used to analyze the π-electron delocalization and charge transfer characteristics.