Photophysics and evidence of excimer formation, linear bipyridines in solution and solid films

Luminescent Self-Assembled Monolayer on Gold Nanoparticles: Tuning of Emission According to the Surface Curvature

Until now, the ability to form a self-assembled monolayer (SAM) on a surface has been investigated according to deposition techniques, which in turn depend on surface-coater interactions. In this paper, we pursued two goals: to form a SAM on a gold nanosurface and to correlate its formation to the nanosurface curvature. To achieve these objectives, gold nanoparticles of different shapes (spheres, rods, and triangles) were functionalized with a luminescent thiolated bipyridine (Bpy-SH), and the SAM formation was studied by investigating the photo-physics of Bpy-SH. We have shown that emission wavelength and excited-state lifetime of Bpy-SH are strongly correlated to the formation of specific aggregates within SAMs, the nature of these aggregates being in close correlation to the shape of the nanoparticles. Micro-Raman spectroscopy investigation was used to test the SERS effect of gold nanoparticles on thiolated bipyridine forming SAMs.

Trace-Level Humidity Sensing from Commercial Organic Solvents and Food Products by an AIE/ESIPT-Triggered Piezochromic Luminogen and ppb-Level "OFF-ON-OFF" Sensing of Cu2+: A Combined Experimental and Theoretical Outcome

Selective and sensitive moisture sensors have attracted immense attention due to their ability to monitor the humidity content in industrial solvents, food products, etc., for regulating industrial safety management. Herein, a hydroxy naphthaldehyde-based piezochromic luminogen, namely, 1-{[(2-hydroxyphenyl)imino]methyl}naphthalen-2-ol (NAP-1), has been synthesized and its photophysical and molecular sensing properties have been investigated by means of various spectroscopic tools. Owing to the synergistic effect of both aggregation-induced emission (AIE) and excited-state intramolecular proton transfer (ESIPT) along with the restriction of C=N isomerization, the probe shows bright yellowish-green-colored keto emission with high quantum yield after the interaction with a trace amount of water. This makes NAP-1 a potential sensor for monitoring water content in the industrial solvents with very low detection limits of 0.033, 0.032, 0.034, and 0.033% (v/v) from tetrahydrofuran (THF), acetone, dimethyl sulfoxide (DMSO), and methanol, respectively. The probe could be used in the food industry to detect trace moisture in the raw food samples. The reversible switching behavior of NAP-1 makes it suitable for designing an INHIBIT logic gate with an additional application in inkless writing. In addition, an Internet of Things-(IoT) based prototype device has been proposed for on-site monitoring of the moisture content by a smartphone via Bluetooth or Wi-Fi. The aggregated probe also has the ability to recognize Cu²⁺ from a purely aqueous medium via the chelation-enhanced quenching (CHEQ) mechanism, leading to ∼84% fluorescence quenching with a Stern-Volmer quenching constant of 1.46 × 10⁴ M^-1 and with an appreciably low detection threshold of 57.2 ppb, far below than recommended by the World Health Organization (WHO) and the United States Environmental Protection Agency (U.S. EPA). The spectroscopic and theoretical calculations (density functional theory (DFT), time-dependent DFT (TD-DFT), and natural bond orbital (NBO) analysis) further empower the understanding of the mechanistic course of the interaction of the host-guest recognition event.