Thin film based on gold nanoparticles or AuNPs is typically used as catalyst in the industrial processes due to their high stability and good reusability. In this work, a thin AuNPs-silica composite film was fabricated firstly from sol-gel method by mixing gold(I) pyrazolate complex to medium comprised of ethanol, deionized water, and hydrochloric acid, followed by addition of tetrabutyl orthosilicate as silica source. Next, 70 μL of the sol-gel solution were spin-coated on several type of substrates such as glass, anodized aluminium oxide or AAO, and combination of both to yield gold complex/silica composite thin film. It was found that gold complex/silica composite film fabricated on combination of both AAO-glass substrate gave the best quality based on its surface thickness, layer uniformity and film brittleness. Later, the thin film was selected and subjected to thermal hydrogen reduction at 210 °C for 2 hours to facilitate the formation of gold nanoparticles to give AuNPs/silica_AAO-glass film. Before the heat treatment, the light-brownish colour of the original gold complex/silica_AAO-glass film in daylight will appear as a pinkish red film under UV light, suggesting the interaction between gold atoms as supported by its luminescence spectrum at 692 nm. Upon heat treatment, the resulting AuNPs/silica_AAO-glass film gave a deep-red colour indicating the successful formation of AuNPs. The presence of AuNPs in the film was further confirmed based on its absorption peak at 545 nm, X-ray diffraction pattern at 2θ= 38.20º for d111plane in wide-angle region, transmission electron microscopy images showing a small and sphere shape particles as well as its elemental composition in energy dispersive X-ray analysis. Moreover, scanning electron microscope images of AuNPs/silica_AAO-glass film also suggested that the AAO pores is fully filled with the composite and is in accordance with its surface roughness study via atomic force microscopy analysis.

The methodical study of trinuclear copper(I) metal complexes phosphorescent vapochromic chemosensor via metal-metal interactions for sensing various volatile organic compounds has piqued the interest of many researchers. Herein, we highlighted the performance of chemosensors trinuclear copper(I) pyrazolate complexes (2Pz1‒2Pz5) with different molecular design short alkyl side chains from the respective pyrazole ligands. The synthesized complexes had demonstrated a high phosphorescent sensing capacity of various alcohol derivatives. Due to weak metal-metal interactions, the complexes give emission bands centered around 553-644 nm at an excitation of 280 nm. We found that the only 2Pz3 chemosensors showed quenching phenomena with a significant decrease in its emission intensity of 100% for exposure in 5 minutes with irreversible performance. Interestingly, we also found that the shifting of the emission center due to the disruption of metal-metal interaction performed by chemosensor 2Pz5 resulting in the best detection performance of methanol and ethanol (∆λ= 60 nm) and propanol (∆λ = 22 nm) showing autonomous recovery within 15 minutes. Based on the findings, the specific balance, such as rigidity and amphiphilicity in the molecular design of chemosensors, is important for the detection of vapors via supramolecular interactions.

The scientific investigation based on the molecular design of aromatic compounds for high-performance chemosensor is challenging. This is because their multiplex interactions at the molecular level should be precisely determined before the desired compounds can be successfully used as sensing materials. Herein, we report on the molecular design of chemosensors based on aromatic structures of benzene as the organic motif of benzene-1,3,5-tricarboxamides (BTA), as well as the benzene pyrazole complexes (BPz) side chain, respectively. In the case of BTA, the aromatic benzene acts as the centre to allow the formation of π–π stacking for one-dimensional materials having rod-like arrangements that are stabilized by threefold hydrogen bonding. We found that when nitrate was applied, the rod-like BTA spontaneously formed into a random aggregate due to the deformation of its hydrogen bonding to form inactive nitroso groups for non-optical sensing capability. For the optical chemosensor, the aromatic benzene is decorated as a side-chain of BPz to ensure that cage-shaped molecules make maximum use of their centre providing metal-metal interactions for fluorescence-based sensing materials. In particular, when exposed to benzene, Cu-BPz displayed a blue-shift of its original emission band from 616 to 572 nm (Δ = 44 nm) and emitted bright orange to green emission colours. We also observe a different mode of fluorescence-based sensing materials for Au-BPz, which shows a particular quenching mechanism resulting in 81% loss of its original intensity on benzene exposure to give less red-orange emission (λ = 612 nm). The BTA and BPz synthesized are promising high-performance supramolecular chemosensors based on the non-optical and optical sensing capability of a particular interest analyte.

Gold(I) pyrazolate complex ([Au3Pz3]C10TEG) has been widely studied due to its interesting liquid crystalline properties by exhibiting the discotic hexagonal columnar arrangement. Generally, the liquid crystalline properties of the gold complex were confirmed based on their differential scanning calorimetry thermogram and polarized optical microscopy (POM) images. However, there is still no in-depth study on the phase transition in liquid crystals of [Au3Pz3]C10TEG especially on its structural change at variable temperature. In this study, the resulting liquid crystalline properties of [Au3Pz3]C10TEG upon being heated and cooled was extensively demonstrated via variable-temperature POM (VT-POM) and small angle X-ray scattering (VT-SAXS). Based on the VT-POM images, it was indicated that [Au3Pz3]C10TEG displayed a fan-shaped texture for typical arrangements of discotic hexagonal columnar of liquid crystals. Moreover, VT-SAXS results was in good agreement with the VT-POM images as it showed that [Au3Pz3]C10TEG might consist of two types of stacking system, which are ordered and disordered hexagonal discotic arrangements. Likewise, VT-SAXS analysis also demonstrated that hexagonal columnar mesophase of [Au3Pz3]C10TEG could be recovered even after the heating and cooling for two cycles.