Benzimidazolic coordination compounds with metals or lanthanides have attracted the interest of scientists due to their electronic properties, such as luminescence, semiconducting behaviour and catalytic. They find use, for example, in optoelectronics. This study investigates the photophysical, electronic, and electrochemical properties of benzimidazole-based coordination complexes formed from the reaction of a Schiff base with Ru³⁺ or La³⁺ ions. We present the synthesis of a Schiff base and its benzimidazole complexes via coordination with RuCl₃∙xH₂O or La(NO₃)₃∙5H₂O and their characterisation using NMR, FTIR, UV–Vis, EPR spectroscopies, electrochemical analysis, SEM–EDS and quantum mechanical calculations. The results show that coordination with Ru³⁺ and La³⁺ stabilises organic radicals. Optical band gap analysis indicates metal coordination slightly lowers the energy gap, confirming their semiconductor behaviour. UV–Vis and emission spectroscopy revealed Förster Resonance Energy Transfer (FRET), metal-to-ligand (M→L) and ligand-to-metal (L→M) energy transfer phenomena. Electrochemical studies indicate that the lanthanum complex exhibits oxidative photocatalysis due to L→M energy transfer, while the ruthenium complex exhibits reductive photocatalysis due to M→L energy transfer. The findings highlight the potential of these benzimidazole-based coordination complexes in applications ranging from electronics to catalysis. Graphical Abstract

Silica nanostructures are attractive platforms for hybrid nanomaterials because of their chemical stability and versatile surface functionalization. Here, spherical SiO₂ nanoparticles were synthesized by a modified Stöber method, functionalized with (3-aminopropyl)triethoxysilane (APTES), and decorated with gold nanoparticles (AuNPs) formed using an inorganic stabilization strategy involving OH⁻ and Cl⁻ ions, without conventional organic AuNP capping agents. Complementary characterization by Fourier-transform infrared spectroscopy (FTIR), ultraviolet–visible diffuse reflectance spectroscopy (UV–VIS DRS), X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) supported the sequential surface modification and formation of the SiO₂–APTES–AuNPs hybrid material. TEM yielded average diameters of 100.81 ± 1.74 nm for SiO₂ nanoparticles (n = 50) and 2.00 ± 0.31 nm for supported AuNPs (n = 80). Methylene blue (MB) was subsequently used for a proof-of-concept Raman evaluation. At 10⁻³ and 10⁻⁴ M MB, relative Raman signal-amplification ratios of approximately 7.5 and 3.5, respectively, were obtained from the integrated response near 1620 cm⁻¹; these values are not conventional surface-enhanced Raman scattering (SERS) enhancement factors. At 10⁻⁶ M, a fluorescence-like background was observed without establishing metal-enhanced fluorescence. Density functional theory calculations using an Au₃₂ cluster provided qualitative insight into local S···Au and π···Au interactions. Overall, these results establish an inorganic SiO₂-AuNPs as a physicochemically characterized hybrid nanomaterial prepared through an inorganic AuNP-stabilization strategy and support its further investigation in Raman-based applications.