Theoretical study of the effect of the inclusion of aromatic heterocyclic compounds in Cu(I) complexes: structure, optoelectronics, and adsorption properties, and their evaluation as dyes in DSSCs.

CONTEXT: A theoretical investigation of 28 homoleptic Cu(I) complexes was conducted to assess their suitability as sensitizers in dye-sensitized solar cells (DSSCs). Two ligand families, triazolylpyridine (G1) and imidazopyridine-pyridine (G2), were systematically functionalized with heteroaromatic substituents derived from pyridine, furan, pyrrole, and thiophene. Pyridine- and thiophene-based spacers produced substantial bathochromic shifts in the absorption maxima, which reached 492 nm, and reduced the HOMO-LUMO energy gaps to values as low as 3.33 eV. These modifications also decreased the chemical hardness (η) and increased the electrophilicity (ω), thereby promoting intramolecular charge transfer and enhancing electron-accepting ability. In contrast, furan- and pyrrole-derived substituents induced only minor electronic changes but increased the propensity to form dual-bidentate or multidentate adsorption motifs on TiO2 surfaces, resulting in stronger interfacial binding. An integrated DSSC index (Di), combining structural, optoelectronic, reactivity, and photovoltaic parameters, identified the G2 family as the most favorable structural framework, with G2ANNC (Di = 0.6096) emerging as the leading sensitizer candidate. Overall, these results demonstrate the potential of these Cu(I) complexes for DSSC applications and provide a systematic framework for their rational design. METHODS: Minimum-energy geometries were determined in ethanol using the M06 functional, with the 6-31G(d) basis set for nonmetal atoms, the DZVP basis set for Cu, and the IEF-PCM solvation model as implemented in Gaussian 16. UV-Vis transitions and excited-state energies were calculated by TD-DFT at the same level of theory for 20 excited states. Electronic transitions were analyzed using AOMix, whereas hole - electron distributions and natural transition orbitals were evaluated using Multiwfn. Photovoltaic parameters, including the light-harvesting efficiency (LHE), excited-state lifetimes, and thermodynamic driving forces for electron injection, dye regeneration, and recombination, were quantified. Bulk anatase TiO2 and an expanded (TiO2)96 slab were optimized using the tiorg-0-1 and mio parameter sets in DFTB + 24.1. Slab reoptimization and dye-surface interactions were evaluated using GFN1-xTB at the Γ point. The candidates were globally evaluated and ranked using a custom Python script. Molecular and crystal structures were visualized using VESTA 3.90.5a.