Perylene Diimide Based Fluorescent Sensors for Drug Simulant Detection: The Effect of Alkyl-Chain Branching on Film Morphology, Exciton Diffusion, Vapor Diffusion, and Sensing Response

Molecular design and architectonics towards film-based fluorescent sensing

The past few decades have witnessed encouraging progress in the development of high-performance film-based fluorescent sensors (FFSs) for detecting explosives, illicit drugs, chemical warfare agents (CWAs), and hazardous volatile organic chemicals (VOCs), among others. Several FFSs have transitioned from laboratory research to real-world applications, demonstrating their practical relevance. At the heart of FFS technology lies the sensing films, which play a crucial role in determining the analytes and the resulting signals. The selection of sensing fluorophores and the fabrication strategies employed in film construction are key factors that influence the fluorescence properties, active-layer structures, and overall sensing behaviors of these films. This review examines the progress and innovations in the research field of FFSs over the past two decades, focusing on advancements in fluorophore design and active-layer structural engineering. It underscores popular sensing fluorophore scaffolds and the dynamics of excited state processes. Additionally, it delves into six distinct categories of film fabrication technologies and strategies, providing insights into their advantages and limitations. This review further addresses important considerations such as photostability and substrate effects. Concluding with an overview of the field's challenges and prospects, it sheds light on the potential for further development in this burgeoning area.

Theoretical Study of Strong Coupling between Molecular Shells and Chiral Plasmons of Gold Nanoparticles Helices

Chiral plasmonic nanostructures can produce strong chiral optical responses and have potential applications in photonics. Experimentally, metallic nanoparticle helices have been synthesized to achieve strong chiral responses. Strong coupling effects between the quantum emitters and the plasmon have attracted significant attention in the past decade and have been recently extended to the chiral plasmon of nanostructures. However, the strong coupling between molecules and metallic nanosphere helices has not been reported yet. In this article we study theoretically such an effect and examine the modulation of chiral and coupling effects by illumination light and molecular layer thickness. Our study may guide further experimental studies.

Utilizing Different Diffusion Mechanisms for Thin Film Fluorescence-Based Detection and Discrimination of Illicit Drug Vapors

Film-based fluorescence sensors have been demonstrated to be powerful tools for real-time detection of trace chemical vapors. While explosive vapor detection via fluorescence quenching has been widely explored, fluorescence-based real-time detection and identification of illicit drug vapors remains a challenge. Here, we report two perylene diimide-based sensing materials, P1 and P2, incorporating 2,2-dihexyloctanyl chains and 4-[tris(4-{tert-butyl}phenyl)methyl]phenyl moieties at the imide positions, respectively. Quartz crystal microbalance with in situ photoluminescence measurements showed that N-methylphenethylamine, a simulant of methamphetamine (MA), diffused into films of P1 and P2 via Fickian and case-II mechanisms, respectively. The difference in the analyte diffusion mechanism led to P2 showing significantly faster luminescence quenching but slower luminescence recovery compared to P1. Finally, the different diffusion mechanisms were used as the basis for developing a simple sensor array based on P1 and P2 that could selectively detect free-base illicit drugs (MA, cocaine, and tetrahydrocannabinol) from potential interferants (organic amines, alcohol, and cosmetics) within 40 s.