Abstract

Lanthanide (Ln³⁺) ions are known for their unique near-infrared (NIR) luminescence resulting from forbidden 4f–4f (f–f) transitions, typically enabled through sensitization by antenna ligands. In this study, we present a homologous series of [L₂–Zn₂–Ln] complexes adopting a sandwich structure, where two ligands (L) coordinate symmetrically around the Ln center via zinc (Zn²⁺) nodes. Photophysical measurements in both the visible and NIR regions indicate a notable enhancement in NIR emission intensity in these sandwich complexes compared to their mono-ligand analogs. A key observation is the quenching of singlet-to-ground state (S₁ → S₀) fluorescence from the ligand, suggesting efficient energy transfer from the excited ligand to the Ln³⁺ ion. This enhanced transfer is attributed to improved electronic coupling and spatial proximity facilitated by the sandwich architecture. The results demonstrate that ligand environment and structural symmetry critically influence NIR luminescence. These findings establish [L₂–Zn₂–Ln] complexes as promising candidates for developing advanced NIR-emitting materials for use in optical sensing and optoelectronic applications.

Biography

The Department of Chemistry at Malaviya National Institute of Technology (MNIT Jaipur), Jaipur, Rajasthan, India, is dedicated to excellence in teaching and research in chemical sciences. The department focuses on key areas such as materials chemistry, nanotechnology, environmental chemistry, and analytical sciences, promoting innovation, interdisciplinary research, and academic development. It is committed to providing strong scientific training and contributing to advancements in science and technology.