Amplified Excited-State Diverse Effects Arising from Ligand Regioisomerism in Cu(I) Complexes for Advanced Applications

Abstract

Designing earth-abundant photoactive coordination complexes that combine molecular tunability with device-relevant performance is essential to advance next-generation optoelectronic and solar-energy technologies. In this work, two heteroleptic Cu(I) complexes were synthesised using regioisomeric diimine ligands obtained through keto-enol tautomerism of a common precursor. Despite their close structural similarity, the complexes exhibit pronounced differences in photophysical and electrochemical behaviour. In the solid state, both compounds show phosphorescent emission, whereas at room temperature one complex displays characteristics consistent with thermally activated delayed fluorescence.Quantum -chemical calculations reveal a relatively large singlet-triplet energy gap for the charge-transfer states in the triplet geometry, and the involvement of a ligand-centered triplet state cannot be excluded. Preliminary photoelectrochemical measurements further demonstrate that simple physisorption of the complexes onto TiO₂ yields measurable photocurrent generation. These results highlight the significant impact of ligand regiochemistry on the excited-state properties and functional performance of Cu(I) complexes.