Porphyrin-Fused <i>N</i> -Heterocyclic Carbene Monolayers on Gold Surfaces and Nanoparticles for Nitric Oxide Detection via Surface-Enhanced Raman Spectroscopy

N-Heterocyclic carbenes (NHCs) have emerged as promising nanoscale surface modifiers, enabling the formation of self-assembled monolayers (SAMs) on both flat surfaces and nanoparticles. However, most NHC-based adsorbates are derived from benzimidazole, with a few examples incorporating secondary metal coordination. Herein, we present the first example of a porphyrin-fused NHC monolayer on a gold surface. To prevent iodide contamination from conventional methylation reagents, dimethyl sulfate was used as an alternative. The resulting monolayer was thoroughly characterized by X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS), and surface-enhanced Raman spectroscopy (SERS). Furthermore, coordination with Ni(II) or Co(II) at the porphyrin core demonstrated its potential for nitric oxide (NO) detection. The monolayer exhibited a moderate thermal stability. Additionally, porphyrin-fused NHCs were incorporated into gold nanoparticles by using both top-down and bottom-up strategies. The resulting nanoparticles were characterized by transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), and UV–vis spectroscopy. This work introduces a strategy for the nanoscale modification of porphyrin-fused NHCs on surfaces and nanoparticles, paving the way for future molecular complex-modified metal surface applications in sensing and catalysis.