Coordination-Induced Tuning of Ligand-Centered Red Emission in a cis-[Cd(Tz)2(py)2] Complex for Light-Emitting Diodes

TL;DR

This study reports a new Cd(II) complex with ligand-centered red emission, showing potential for light-emitting diodes due to its broad, warm emission spectrum and semiconductor-like properties.

Contribution

The paper introduces a novel cadmium complex with ligand-centered red emission, demonstrating its structural, spectroscopic, and optoelectronic properties relevant for LED applications.

Findings

Broad emission band at 500–850 nm with enhanced red contribution upon coordination.

Direct optical band gap of 1.83 eV indicating semiconductor-like behavior.

Emission mainly ligand-centered, consistent with d10 Cd(II) configuration.

Abstract

Organic--inorganic complexes are promising materials for light-emitting applications. Here, we report a new organometallic complex, cis-[Cd(Tz)$_2$(py)$_2$], featuring a distorted octahedral Cd(II) coordination environment. IR and Raman spectroscopy reveal pronounced coordination-induced changes, particularly in the Raman response of the triazene moiety, indicating electronic and structural perturbation upon Cd(II) complexation. Hirshfeld surface analysis shows that the crystal packing is mainly governed by H$\cdots$H, O$\cdots$H/H$\cdots$O, and C$\cdots$H/H$\cdots$C contacts, whereas $\pi$--$\pi$ stacking interactions contribute modestly. Solid-state UV--Vis spectroscopy reveals broad absorption from $\sim$700 to 200 nm and a direct optical band gap of 1.83 eV, indicating semiconductor-like behavior. Photoluminescence measurements show a broad emission band at 500--850 nm with enhanced red contribution upon coordination. The emission is mainly assigned to ligand-centered transitions ($\pi \rightarrow \pi^*$ and $n \rightarrow \pi^*$), consistent with the $d^{10}$ configuration of Cd(II), which suppresses metal-centered and charge-transfer processes. The CIE chromaticity coordinates confirm warm emission, highlighting the potential of cis-[Cd(Tz)$_2$(py)$_2$] for red-emitting optoelectronic applications.